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linux/arch/arm64/kernel/module-plts.c

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arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
/*
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
* Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/elf.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sort.h>
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
static bool in_init(const struct module *mod, void *loc)
{
return (u64)loc - (u64)mod->init_layout.base < mod->init_layout.size;
}
u64 module_emit_plt_entry(struct module *mod, void *loc, const Elf64_Rela *rela,
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
Elf64_Sym *sym)
{
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
&mod->arch.init;
struct plt_entry *plt = (struct plt_entry *)pltsec->plt->sh_addr;
int i = pltsec->plt_num_entries;
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
u64 val = sym->st_value + rela->r_addend;
arm64: module-plts: factor out PLT generation code for ftrace To allow the ftrace trampoline code to reuse the PLT entry routines, factor it out and move it into asm/module.h. Cc: <stable@vger.kernel.org> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
2017-11-20 17:41:29 +00:00
plt[i] = get_plt_entry(val);
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
/*
* Check if the entry we just created is a duplicate. Given that the
* relocations are sorted, this will be the last entry we allocated.
* (if one exists).
*/
arm64: module-plts: factor out PLT generation code for ftrace To allow the ftrace trampoline code to reuse the PLT entry routines, factor it out and move it into asm/module.h. Cc: <stable@vger.kernel.org> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
2017-11-20 17:41:29 +00:00
if (i > 0 && plt_entries_equal(plt + i, plt + i - 1))
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
return (u64)&plt[i - 1];
pltsec->plt_num_entries++;
arm64: module: don't BUG when exceeding preallocated PLT count When PLTs are emitted at relocation time, we really should not exceed the number that we counted when parsing the relocation tables, and so currently, we BUG() on this condition. However, even though this is a clear bug in this particular piece of code, we can easily recover by failing to load the module. So instead, return 0 from module_emit_plt_entry() if this condition occurs, which is not a valid kernel address, and can hence serve as a flag value that makes the relocation routine bail out. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-03-06 17:15:31 +00:00
if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
return 0;
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
return (u64)&plt[i];
}
arm64/kernel: don't ban ADRP to work around Cortex-A53 erratum #843419 Working around Cortex-A53 erratum #843419 involves special handling of ADRP instructions that end up in the last two instruction slots of a 4k page, or whose output register gets overwritten without having been read. (Note that the latter instruction sequence is never emitted by a properly functioning compiler, which is why it is disregarded by the handling of the same erratum in the bfd.ld linker which we rely on for the core kernel) Normally, this gets taken care of by the linker, which can spot such sequences at final link time, and insert a veneer if the ADRP ends up at a vulnerable offset. However, linux kernel modules are partially linked ELF objects, and so there is no 'final link time' other than the runtime loading of the module, at which time all the static relocations are resolved. For this reason, we have implemented the #843419 workaround for modules by avoiding ADRP instructions altogether, by using the large C model, and by passing -mpc-relative-literal-loads to recent versions of GCC that may emit adrp/ldr pairs to perform literal loads. However, this workaround forces us to keep literal data mixed with the instructions in the executable .text segment, and literal data may inadvertently turn into an exploitable speculative gadget depending on the relative offsets of arbitrary symbols. So let's reimplement this workaround in a way that allows us to switch back to the small C model, and to drop the -mpc-relative-literal-loads GCC switch, by patching affected ADRP instructions at runtime: - ADRP instructions that do not appear at 4k relative offset 0xff8 or 0xffc are ignored - ADRP instructions that are within 1 MB of their target symbol are converted into ADR instructions - remaining ADRP instructions are redirected via a veneer that performs the load using an unaffected movn/movk sequence. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [will: tidied up ADRP -> ADR instruction patching.] [will: use ULL suffix for 64-bit immediate] Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-03-06 17:15:33 +00:00
#ifdef CONFIG_ARM64_ERRATUM_843419
u64 module_emit_adrp_veneer(struct module *mod, void *loc, u64 val)
{
struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
&mod->arch.init;
struct plt_entry *plt = (struct plt_entry *)pltsec->plt->sh_addr;
int i = pltsec->plt_num_entries++;
u32 mov0, mov1, mov2, br;
int rd;
if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
return 0;
/* get the destination register of the ADRP instruction */
rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD,
le32_to_cpup((__le32 *)loc));
/* generate the veneer instructions */
mov0 = aarch64_insn_gen_movewide(rd, (u16)~val, 0,
AARCH64_INSN_VARIANT_64BIT,
AARCH64_INSN_MOVEWIDE_INVERSE);
mov1 = aarch64_insn_gen_movewide(rd, (u16)(val >> 16), 16,
AARCH64_INSN_VARIANT_64BIT,
AARCH64_INSN_MOVEWIDE_KEEP);
mov2 = aarch64_insn_gen_movewide(rd, (u16)(val >> 32), 32,
AARCH64_INSN_VARIANT_64BIT,
AARCH64_INSN_MOVEWIDE_KEEP);
br = aarch64_insn_gen_branch_imm((u64)&plt[i].br, (u64)loc + 4,
AARCH64_INSN_BRANCH_NOLINK);
plt[i] = (struct plt_entry){
cpu_to_le32(mov0),
cpu_to_le32(mov1),
cpu_to_le32(mov2),
cpu_to_le32(br)
};
return (u64)&plt[i];
}
#endif
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
#define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b))
static int cmp_rela(const void *a, const void *b)
{
const Elf64_Rela *x = a, *y = b;
int i;
/* sort by type, symbol index and addend */
i = cmp_3way(ELF64_R_TYPE(x->r_info), ELF64_R_TYPE(y->r_info));
if (i == 0)
i = cmp_3way(ELF64_R_SYM(x->r_info), ELF64_R_SYM(y->r_info));
if (i == 0)
i = cmp_3way(x->r_addend, y->r_addend);
return i;
}
static bool duplicate_rel(const Elf64_Rela *rela, int num)
{
/*
* Entries are sorted by type, symbol index and addend. That means
* that, if a duplicate entry exists, it must be in the preceding
* slot.
*/
return num > 0 && cmp_rela(rela + num, rela + num - 1) == 0;
}
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
static unsigned int count_plts(Elf64_Sym *syms, Elf64_Rela *rela, int num,
arm64/kernel: don't ban ADRP to work around Cortex-A53 erratum #843419 Working around Cortex-A53 erratum #843419 involves special handling of ADRP instructions that end up in the last two instruction slots of a 4k page, or whose output register gets overwritten without having been read. (Note that the latter instruction sequence is never emitted by a properly functioning compiler, which is why it is disregarded by the handling of the same erratum in the bfd.ld linker which we rely on for the core kernel) Normally, this gets taken care of by the linker, which can spot such sequences at final link time, and insert a veneer if the ADRP ends up at a vulnerable offset. However, linux kernel modules are partially linked ELF objects, and so there is no 'final link time' other than the runtime loading of the module, at which time all the static relocations are resolved. For this reason, we have implemented the #843419 workaround for modules by avoiding ADRP instructions altogether, by using the large C model, and by passing -mpc-relative-literal-loads to recent versions of GCC that may emit adrp/ldr pairs to perform literal loads. However, this workaround forces us to keep literal data mixed with the instructions in the executable .text segment, and literal data may inadvertently turn into an exploitable speculative gadget depending on the relative offsets of arbitrary symbols. So let's reimplement this workaround in a way that allows us to switch back to the small C model, and to drop the -mpc-relative-literal-loads GCC switch, by patching affected ADRP instructions at runtime: - ADRP instructions that do not appear at 4k relative offset 0xff8 or 0xffc are ignored - ADRP instructions that are within 1 MB of their target symbol are converted into ADR instructions - remaining ADRP instructions are redirected via a veneer that performs the load using an unaffected movn/movk sequence. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [will: tidied up ADRP -> ADR instruction patching.] [will: use ULL suffix for 64-bit immediate] Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-03-06 17:15:33 +00:00
Elf64_Word dstidx, Elf_Shdr *dstsec)
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
{
unsigned int ret = 0;
Elf64_Sym *s;
int i;
for (i = 0; i < num; i++) {
arm64/kernel: don't ban ADRP to work around Cortex-A53 erratum #843419 Working around Cortex-A53 erratum #843419 involves special handling of ADRP instructions that end up in the last two instruction slots of a 4k page, or whose output register gets overwritten without having been read. (Note that the latter instruction sequence is never emitted by a properly functioning compiler, which is why it is disregarded by the handling of the same erratum in the bfd.ld linker which we rely on for the core kernel) Normally, this gets taken care of by the linker, which can spot such sequences at final link time, and insert a veneer if the ADRP ends up at a vulnerable offset. However, linux kernel modules are partially linked ELF objects, and so there is no 'final link time' other than the runtime loading of the module, at which time all the static relocations are resolved. For this reason, we have implemented the #843419 workaround for modules by avoiding ADRP instructions altogether, by using the large C model, and by passing -mpc-relative-literal-loads to recent versions of GCC that may emit adrp/ldr pairs to perform literal loads. However, this workaround forces us to keep literal data mixed with the instructions in the executable .text segment, and literal data may inadvertently turn into an exploitable speculative gadget depending on the relative offsets of arbitrary symbols. So let's reimplement this workaround in a way that allows us to switch back to the small C model, and to drop the -mpc-relative-literal-loads GCC switch, by patching affected ADRP instructions at runtime: - ADRP instructions that do not appear at 4k relative offset 0xff8 or 0xffc are ignored - ADRP instructions that are within 1 MB of their target symbol are converted into ADR instructions - remaining ADRP instructions are redirected via a veneer that performs the load using an unaffected movn/movk sequence. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [will: tidied up ADRP -> ADR instruction patching.] [will: use ULL suffix for 64-bit immediate] Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-03-06 17:15:33 +00:00
u64 min_align;
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
switch (ELF64_R_TYPE(rela[i].r_info)) {
case R_AARCH64_JUMP26:
case R_AARCH64_CALL26:
arm64/kernel: don't ban ADRP to work around Cortex-A53 erratum #843419 Working around Cortex-A53 erratum #843419 involves special handling of ADRP instructions that end up in the last two instruction slots of a 4k page, or whose output register gets overwritten without having been read. (Note that the latter instruction sequence is never emitted by a properly functioning compiler, which is why it is disregarded by the handling of the same erratum in the bfd.ld linker which we rely on for the core kernel) Normally, this gets taken care of by the linker, which can spot such sequences at final link time, and insert a veneer if the ADRP ends up at a vulnerable offset. However, linux kernel modules are partially linked ELF objects, and so there is no 'final link time' other than the runtime loading of the module, at which time all the static relocations are resolved. For this reason, we have implemented the #843419 workaround for modules by avoiding ADRP instructions altogether, by using the large C model, and by passing -mpc-relative-literal-loads to recent versions of GCC that may emit adrp/ldr pairs to perform literal loads. However, this workaround forces us to keep literal data mixed with the instructions in the executable .text segment, and literal data may inadvertently turn into an exploitable speculative gadget depending on the relative offsets of arbitrary symbols. So let's reimplement this workaround in a way that allows us to switch back to the small C model, and to drop the -mpc-relative-literal-loads GCC switch, by patching affected ADRP instructions at runtime: - ADRP instructions that do not appear at 4k relative offset 0xff8 or 0xffc are ignored - ADRP instructions that are within 1 MB of their target symbol are converted into ADR instructions - remaining ADRP instructions are redirected via a veneer that performs the load using an unaffected movn/movk sequence. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [will: tidied up ADRP -> ADR instruction patching.] [will: use ULL suffix for 64-bit immediate] Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-03-06 17:15:33 +00:00
if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
break;
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
/*
* We only have to consider branch targets that resolve
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
* to symbols that are defined in a different section.
* This is not simply a heuristic, it is a fundamental
* limitation, since there is no guaranteed way to emit
* PLT entries sufficiently close to the branch if the
* section size exceeds the range of a branch
* instruction. So ignore relocations against defined
* symbols if they live in the same section as the
* relocation target.
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
*/
s = syms + ELF64_R_SYM(rela[i].r_info);
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
if (s->st_shndx == dstidx)
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
break;
/*
* Jump relocations with non-zero addends against
* undefined symbols are supported by the ELF spec, but
* do not occur in practice (e.g., 'jump n bytes past
* the entry point of undefined function symbol f').
* So we need to support them, but there is no need to
* take them into consideration when trying to optimize
* this code. So let's only check for duplicates when
* the addend is zero: this allows us to record the PLT
* entry address in the symbol table itself, rather than
* having to search the list for duplicates each time we
* emit one.
*/
if (rela[i].r_addend != 0 || !duplicate_rel(rela, i))
ret++;
break;
arm64/kernel: don't ban ADRP to work around Cortex-A53 erratum #843419 Working around Cortex-A53 erratum #843419 involves special handling of ADRP instructions that end up in the last two instruction slots of a 4k page, or whose output register gets overwritten without having been read. (Note that the latter instruction sequence is never emitted by a properly functioning compiler, which is why it is disregarded by the handling of the same erratum in the bfd.ld linker which we rely on for the core kernel) Normally, this gets taken care of by the linker, which can spot such sequences at final link time, and insert a veneer if the ADRP ends up at a vulnerable offset. However, linux kernel modules are partially linked ELF objects, and so there is no 'final link time' other than the runtime loading of the module, at which time all the static relocations are resolved. For this reason, we have implemented the #843419 workaround for modules by avoiding ADRP instructions altogether, by using the large C model, and by passing -mpc-relative-literal-loads to recent versions of GCC that may emit adrp/ldr pairs to perform literal loads. However, this workaround forces us to keep literal data mixed with the instructions in the executable .text segment, and literal data may inadvertently turn into an exploitable speculative gadget depending on the relative offsets of arbitrary symbols. So let's reimplement this workaround in a way that allows us to switch back to the small C model, and to drop the -mpc-relative-literal-loads GCC switch, by patching affected ADRP instructions at runtime: - ADRP instructions that do not appear at 4k relative offset 0xff8 or 0xffc are ignored - ADRP instructions that are within 1 MB of their target symbol are converted into ADR instructions - remaining ADRP instructions are redirected via a veneer that performs the load using an unaffected movn/movk sequence. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [will: tidied up ADRP -> ADR instruction patching.] [will: use ULL suffix for 64-bit immediate] Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-03-06 17:15:33 +00:00
case R_AARCH64_ADR_PREL_PG_HI21_NC:
case R_AARCH64_ADR_PREL_PG_HI21:
if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_843419))
break;
/*
* Determine the minimal safe alignment for this ADRP
* instruction: the section alignment at which it is
* guaranteed not to appear at a vulnerable offset.
*
* This comes down to finding the least significant zero
* bit in bits [11:3] of the section offset, and
* increasing the section's alignment so that the
* resulting address of this instruction is guaranteed
* to equal the offset in that particular bit (as well
* as all less signficant bits). This ensures that the
* address modulo 4 KB != 0xfff8 or 0xfffc (which would
* have all ones in bits [11:3])
*/
min_align = 2ULL << ffz(rela[i].r_offset | 0x7);
/*
* Allocate veneer space for each ADRP that may appear
* at a vulnerable offset nonetheless. At relocation
* time, some of these will remain unused since some
* ADRP instructions can be patched to ADR instructions
* instead.
*/
if (min_align > SZ_4K)
ret++;
else
dstsec->sh_addralign = max(dstsec->sh_addralign,
min_align);
break;
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
}
}
return ret;
}
int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod)
{
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
unsigned long core_plts = 0;
unsigned long init_plts = 0;
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
Elf64_Sym *syms = NULL;
arm64: ftrace: emit ftrace-mod.o contents through code When building the arm64 kernel with both CONFIG_ARM64_MODULE_PLTS and CONFIG_DYNAMIC_FTRACE enabled, the ftrace-mod.o object file is built with the kernel and contains a trampoline that is linked into each module, so that modules can be loaded far away from the kernel and still reach the ftrace entry point in the core kernel with an ordinary relative branch, as is emitted by the compiler instrumentation code dynamic ftrace relies on. In order to be able to build out of tree modules, this object file needs to be included into the linux-headers or linux-devel packages, which is undesirable, as it makes arm64 a special case (although a precedent does exist for 32-bit PPC). Given that the trampoline essentially consists of a PLT entry, let's not bother with a source or object file for it, and simply patch it in whenever the trampoline is being populated, using the existing PLT support routines. Cc: <stable@vger.kernel.org> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
2017-11-20 17:41:30 +00:00
Elf_Shdr *tramp = NULL;
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
int i;
/*
* Find the empty .plt section so we can expand it to store the PLT
* entries. Record the symtab address as well.
*/
for (i = 0; i < ehdr->e_shnum; i++) {
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
mod->arch.core.plt = sechdrs + i;
else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt"))
mod->arch.init.plt = sechdrs + i;
arm64: ftrace: emit ftrace-mod.o contents through code When building the arm64 kernel with both CONFIG_ARM64_MODULE_PLTS and CONFIG_DYNAMIC_FTRACE enabled, the ftrace-mod.o object file is built with the kernel and contains a trampoline that is linked into each module, so that modules can be loaded far away from the kernel and still reach the ftrace entry point in the core kernel with an ordinary relative branch, as is emitted by the compiler instrumentation code dynamic ftrace relies on. In order to be able to build out of tree modules, this object file needs to be included into the linux-headers or linux-devel packages, which is undesirable, as it makes arm64 a special case (although a precedent does exist for 32-bit PPC). Given that the trampoline essentially consists of a PLT entry, let's not bother with a source or object file for it, and simply patch it in whenever the trampoline is being populated, using the existing PLT support routines. Cc: <stable@vger.kernel.org> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
2017-11-20 17:41:30 +00:00
else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) &&
!strcmp(secstrings + sechdrs[i].sh_name,
".text.ftrace_trampoline"))
tramp = sechdrs + i;
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
else if (sechdrs[i].sh_type == SHT_SYMTAB)
syms = (Elf64_Sym *)sechdrs[i].sh_addr;
}
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
if (!mod->arch.core.plt || !mod->arch.init.plt) {
pr_err("%s: module PLT section(s) missing\n", mod->name);
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
return -ENOEXEC;
}
if (!syms) {
pr_err("%s: module symtab section missing\n", mod->name);
return -ENOEXEC;
}
for (i = 0; i < ehdr->e_shnum; i++) {
Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset;
int numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela);
Elf64_Shdr *dstsec = sechdrs + sechdrs[i].sh_info;
if (sechdrs[i].sh_type != SHT_RELA)
continue;
/* ignore relocations that operate on non-exec sections */
if (!(dstsec->sh_flags & SHF_EXECINSTR))
continue;
/* sort by type, symbol index and addend */
sort(rels, numrels, sizeof(Elf64_Rela), cmp_rela, NULL);
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
if (strncmp(secstrings + dstsec->sh_name, ".init", 5) != 0)
core_plts += count_plts(syms, rels, numrels,
arm64/kernel: don't ban ADRP to work around Cortex-A53 erratum #843419 Working around Cortex-A53 erratum #843419 involves special handling of ADRP instructions that end up in the last two instruction slots of a 4k page, or whose output register gets overwritten without having been read. (Note that the latter instruction sequence is never emitted by a properly functioning compiler, which is why it is disregarded by the handling of the same erratum in the bfd.ld linker which we rely on for the core kernel) Normally, this gets taken care of by the linker, which can spot such sequences at final link time, and insert a veneer if the ADRP ends up at a vulnerable offset. However, linux kernel modules are partially linked ELF objects, and so there is no 'final link time' other than the runtime loading of the module, at which time all the static relocations are resolved. For this reason, we have implemented the #843419 workaround for modules by avoiding ADRP instructions altogether, by using the large C model, and by passing -mpc-relative-literal-loads to recent versions of GCC that may emit adrp/ldr pairs to perform literal loads. However, this workaround forces us to keep literal data mixed with the instructions in the executable .text segment, and literal data may inadvertently turn into an exploitable speculative gadget depending on the relative offsets of arbitrary symbols. So let's reimplement this workaround in a way that allows us to switch back to the small C model, and to drop the -mpc-relative-literal-loads GCC switch, by patching affected ADRP instructions at runtime: - ADRP instructions that do not appear at 4k relative offset 0xff8 or 0xffc are ignored - ADRP instructions that are within 1 MB of their target symbol are converted into ADR instructions - remaining ADRP instructions are redirected via a veneer that performs the load using an unaffected movn/movk sequence. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [will: tidied up ADRP -> ADR instruction patching.] [will: use ULL suffix for 64-bit immediate] Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-03-06 17:15:33 +00:00
sechdrs[i].sh_info, dstsec);
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
else
init_plts += count_plts(syms, rels, numrels,
arm64/kernel: don't ban ADRP to work around Cortex-A53 erratum #843419 Working around Cortex-A53 erratum #843419 involves special handling of ADRP instructions that end up in the last two instruction slots of a 4k page, or whose output register gets overwritten without having been read. (Note that the latter instruction sequence is never emitted by a properly functioning compiler, which is why it is disregarded by the handling of the same erratum in the bfd.ld linker which we rely on for the core kernel) Normally, this gets taken care of by the linker, which can spot such sequences at final link time, and insert a veneer if the ADRP ends up at a vulnerable offset. However, linux kernel modules are partially linked ELF objects, and so there is no 'final link time' other than the runtime loading of the module, at which time all the static relocations are resolved. For this reason, we have implemented the #843419 workaround for modules by avoiding ADRP instructions altogether, by using the large C model, and by passing -mpc-relative-literal-loads to recent versions of GCC that may emit adrp/ldr pairs to perform literal loads. However, this workaround forces us to keep literal data mixed with the instructions in the executable .text segment, and literal data may inadvertently turn into an exploitable speculative gadget depending on the relative offsets of arbitrary symbols. So let's reimplement this workaround in a way that allows us to switch back to the small C model, and to drop the -mpc-relative-literal-loads GCC switch, by patching affected ADRP instructions at runtime: - ADRP instructions that do not appear at 4k relative offset 0xff8 or 0xffc are ignored - ADRP instructions that are within 1 MB of their target symbol are converted into ADR instructions - remaining ADRP instructions are redirected via a veneer that performs the load using an unaffected movn/movk sequence. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [will: tidied up ADRP -> ADR instruction patching.] [will: use ULL suffix for 64-bit immediate] Signed-off-by: Will Deacon <will.deacon@arm.com>
2018-03-06 17:15:33 +00:00
sechdrs[i].sh_info, dstsec);
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
}
arm64: module: split core and init PLT sections The arm64 module PLT code allocates all PLT entries in a single core section, since the overhead of having a separate init PLT section is not justified by the small number of PLT entries usually required for init code. However, the core and init module regions are allocated independently, and there is a corner case where the core region may be allocated from the VMALLOC region if the dedicated module region is exhausted, but the init region, being much smaller, can still be allocated from the module region. This leads to relocation failures if the distance between those regions exceeds 128 MB. (In fact, this corner case is highly unlikely to occur on arm64, but the issue has been observed on ARM, whose module region is much smaller). So split the core and init PLT regions, and name the latter ".init.plt" so it gets allocated along with (and sufficiently close to) the .init sections that it serves. Also, given that init PLT entries may need to be emitted for branches that target the core module, modify the logic that disregards defined symbols to only disregard symbols that are defined in the same section as the relocated branch instruction. Since there may now be two PLT entries associated with each entry in the symbol table, we can no longer hijack the symbol::st_size fields to record the addresses of PLT entries as we emit them for zero-addend relocations. So instead, perform an explicit comparison to check for duplicate entries. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2017-02-21 22:12:57 +00:00
mod->arch.core.plt->sh_type = SHT_NOBITS;
mod->arch.core.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
mod->arch.core.plt->sh_addralign = L1_CACHE_BYTES;
mod->arch.core.plt->sh_size = (core_plts + 1) * sizeof(struct plt_entry);
mod->arch.core.plt_num_entries = 0;
mod->arch.core.plt_max_entries = core_plts;
mod->arch.init.plt->sh_type = SHT_NOBITS;
mod->arch.init.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
mod->arch.init.plt->sh_addralign = L1_CACHE_BYTES;
mod->arch.init.plt->sh_size = (init_plts + 1) * sizeof(struct plt_entry);
mod->arch.init.plt_num_entries = 0;
mod->arch.init.plt_max_entries = init_plts;
arm64: ftrace: emit ftrace-mod.o contents through code When building the arm64 kernel with both CONFIG_ARM64_MODULE_PLTS and CONFIG_DYNAMIC_FTRACE enabled, the ftrace-mod.o object file is built with the kernel and contains a trampoline that is linked into each module, so that modules can be loaded far away from the kernel and still reach the ftrace entry point in the core kernel with an ordinary relative branch, as is emitted by the compiler instrumentation code dynamic ftrace relies on. In order to be able to build out of tree modules, this object file needs to be included into the linux-headers or linux-devel packages, which is undesirable, as it makes arm64 a special case (although a precedent does exist for 32-bit PPC). Given that the trampoline essentially consists of a PLT entry, let's not bother with a source or object file for it, and simply patch it in whenever the trampoline is being populated, using the existing PLT support routines. Cc: <stable@vger.kernel.org> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
2017-11-20 17:41:30 +00:00
if (tramp) {
tramp->sh_type = SHT_NOBITS;
tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
tramp->sh_addralign = __alignof__(struct plt_entry);
tramp->sh_size = sizeof(struct plt_entry);
}
arm64: add support for module PLTs This adds support for emitting PLTs at module load time for relative branches that are out of range. This is a prerequisite for KASLR, which may place the kernel and the modules anywhere in the vmalloc area, making it more likely that branch target offsets exceed the maximum range of +/- 128 MB. In this version, I removed the distinction between relocations against .init executable sections and ordinary executable sections. The reason is that it is hardly worth the trouble, given that .init.text usually does not contain that many far branches, and this version now only reserves PLT entry space for jump and call relocations against undefined symbols (since symbols defined in the same module can be assumed to be within +/- 128 MB) For example, the mac80211.ko module (which is fairly sizable at ~400 KB) built with -mcmodel=large gives the following relocation counts: relocs branches unique !local .text 3925 3347 518 219 .init.text 11 8 7 1 .exit.text 4 4 4 1 .text.unlikely 81 67 36 17 ('unique' means branches to unique type/symbol/addend combos, of which !local is the subset referring to undefined symbols) IOW, we are only emitting a single PLT entry for the .init sections, and we are better off just adding it to the core PLT section instead. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2015-11-24 11:37:35 +00:00
return 0;
}
Reference in New Issue Copy Permalink