3b23e4991f
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
71 lines
1.8 KiB
C
71 lines
1.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
|
|
/*
|
|
* Copyright (C) 2012 ARM Ltd.
|
|
*/
|
|
#ifndef __ASM_MODULE_H
|
|
#define __ASM_MODULE_H
|
|
|
|
#include <asm-generic/module.h>
|
|
|
|
#define MODULE_ARCH_VERMAGIC "aarch64"
|
|
|
|
#ifdef CONFIG_ARM64_MODULE_PLTS
|
|
struct mod_plt_sec {
|
|
int plt_shndx;
|
|
int plt_num_entries;
|
|
int plt_max_entries;
|
|
};
|
|
|
|
struct mod_arch_specific {
|
|
struct mod_plt_sec core;
|
|
struct mod_plt_sec init;
|
|
|
|
/* for CONFIG_DYNAMIC_FTRACE */
|
|
struct plt_entry *ftrace_trampolines;
|
|
};
|
|
#endif
|
|
|
|
u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs,
|
|
void *loc, const Elf64_Rela *rela,
|
|
Elf64_Sym *sym);
|
|
|
|
u64 module_emit_veneer_for_adrp(struct module *mod, Elf64_Shdr *sechdrs,
|
|
void *loc, u64 val);
|
|
|
|
#ifdef CONFIG_RANDOMIZE_BASE
|
|
extern u64 module_alloc_base;
|
|
#else
|
|
#define module_alloc_base ((u64)_etext - MODULES_VSIZE)
|
|
#endif
|
|
|
|
struct plt_entry {
|
|
/*
|
|
* A program that conforms to the AArch64 Procedure Call Standard
|
|
* (AAPCS64) must assume that a veneer that alters IP0 (x16) and/or
|
|
* IP1 (x17) may be inserted at any branch instruction that is
|
|
* exposed to a relocation that supports long branches. Since that
|
|
* is exactly what we are dealing with here, we are free to use x16
|
|
* as a scratch register in the PLT veneers.
|
|
*/
|
|
__le32 adrp; /* adrp x16, .... */
|
|
__le32 add; /* add x16, x16, #0x.... */
|
|
__le32 br; /* br x16 */
|
|
};
|
|
|
|
static inline bool is_forbidden_offset_for_adrp(void *place)
|
|
{
|
|
return IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) &&
|
|
cpus_have_const_cap(ARM64_WORKAROUND_843419) &&
|
|
((u64)place & 0xfff) >= 0xff8;
|
|
}
|
|
|
|
struct plt_entry get_plt_entry(u64 dst, void *pc);
|
|
bool plt_entries_equal(const struct plt_entry *a, const struct plt_entry *b);
|
|
|
|
static inline bool plt_entry_is_initialized(const struct plt_entry *e)
|
|
{
|
|
return e->adrp || e->add || e->br;
|
|
}
|
|
|
|
#endif /* __ASM_MODULE_H */
|