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ac12cf85d6
* for-next/52-bit-kva: (25 commits) Support for 52-bit virtual addressing in kernel space * for-next/cpu-topology: (9 commits) Move CPU topology parsing into core code and add support for ACPI 6.3 * for-next/error-injection: (2 commits) Support for function error injection via kprobes * for-next/perf: (8 commits) Support for i.MX8 DDR PMU and proper SMMUv3 group validation * for-next/psci-cpuidle: (7 commits) Move PSCI idle code into a new CPUidle driver * for-next/rng: (4 commits) Support for 'rng-seed' property being passed in the devicetree * for-next/smpboot: (3 commits) Reduce fragility of secondary CPU bringup in debug configurations * for-next/tbi: (10 commits) Introduce new syscall ABI with relaxed requirements for pointer tags * for-next/tlbi: (6 commits) Handle spurious page faults arising from kernel space
173 lines
5.0 KiB
C
173 lines
5.0 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org>
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*/
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#include <linux/cache.h>
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#include <linux/crc32.h>
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#include <linux/init.h>
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#include <linux/libfdt.h>
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#include <linux/mm_types.h>
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#include <linux/sched.h>
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#include <linux/types.h>
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#include <asm/cacheflush.h>
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#include <asm/fixmap.h>
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#include <asm/kernel-pgtable.h>
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#include <asm/memory.h>
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#include <asm/mmu.h>
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#include <asm/pgtable.h>
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#include <asm/sections.h>
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u64 __ro_after_init module_alloc_base;
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u16 __initdata memstart_offset_seed;
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static __init u64 get_kaslr_seed(void *fdt)
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{
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int node, len;
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fdt64_t *prop;
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u64 ret;
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node = fdt_path_offset(fdt, "/chosen");
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if (node < 0)
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return 0;
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prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
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if (!prop || len != sizeof(u64))
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return 0;
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ret = fdt64_to_cpu(*prop);
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*prop = 0;
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return ret;
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}
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static __init const u8 *kaslr_get_cmdline(void *fdt)
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{
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static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE;
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if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
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int node;
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const u8 *prop;
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node = fdt_path_offset(fdt, "/chosen");
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if (node < 0)
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goto out;
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prop = fdt_getprop(fdt, node, "bootargs", NULL);
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if (!prop)
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goto out;
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return prop;
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}
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out:
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return default_cmdline;
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}
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/*
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* This routine will be executed with the kernel mapped at its default virtual
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* address, and if it returns successfully, the kernel will be remapped, and
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* start_kernel() will be executed from a randomized virtual offset. The
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* relocation will result in all absolute references (e.g., static variables
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* containing function pointers) to be reinitialized, and zero-initialized
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* .bss variables will be reset to 0.
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*/
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u64 __init kaslr_early_init(u64 dt_phys)
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{
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void *fdt;
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u64 seed, offset, mask, module_range;
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const u8 *cmdline, *str;
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int size;
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/*
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* Set a reasonable default for module_alloc_base in case
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* we end up running with module randomization disabled.
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*/
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module_alloc_base = (u64)_etext - MODULES_VSIZE;
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__flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base));
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/*
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* Try to map the FDT early. If this fails, we simply bail,
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* and proceed with KASLR disabled. We will make another
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* attempt at mapping the FDT in setup_machine()
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*/
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early_fixmap_init();
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fdt = fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
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if (!fdt)
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return 0;
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/*
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* Retrieve (and wipe) the seed from the FDT
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*/
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seed = get_kaslr_seed(fdt);
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if (!seed)
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return 0;
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/*
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* Check if 'nokaslr' appears on the command line, and
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* return 0 if that is the case.
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*/
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cmdline = kaslr_get_cmdline(fdt);
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str = strstr(cmdline, "nokaslr");
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if (str == cmdline || (str > cmdline && *(str - 1) == ' '))
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return 0;
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/*
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* OK, so we are proceeding with KASLR enabled. Calculate a suitable
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* kernel image offset from the seed. Let's place the kernel in the
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* middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of
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* the lower and upper quarters to avoid colliding with other
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* allocations.
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* Even if we could randomize at page granularity for 16k and 64k pages,
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* let's always round to 2 MB so we don't interfere with the ability to
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* map using contiguous PTEs
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*/
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mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1);
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offset = BIT(VA_BITS_MIN - 3) + (seed & mask);
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/* use the top 16 bits to randomize the linear region */
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memstart_offset_seed = seed >> 48;
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if (IS_ENABLED(CONFIG_KASAN))
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/*
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* KASAN does not expect the module region to intersect the
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* vmalloc region, since shadow memory is allocated for each
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* module at load time, whereas the vmalloc region is shadowed
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* by KASAN zero pages. So keep modules out of the vmalloc
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* region if KASAN is enabled, and put the kernel well within
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* 4 GB of the module region.
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*/
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return offset % SZ_2G;
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if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {
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/*
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* Randomize the module region over a 2 GB window covering the
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* kernel. This reduces the risk of modules leaking information
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* about the address of the kernel itself, but results in
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* branches between modules and the core kernel that are
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* resolved via PLTs. (Branches between modules will be
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* resolved normally.)
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*/
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module_range = SZ_2G - (u64)(_end - _stext);
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module_alloc_base = max((u64)_end + offset - SZ_2G,
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(u64)MODULES_VADDR);
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} else {
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/*
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* Randomize the module region by setting module_alloc_base to
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* a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE,
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* _stext) . This guarantees that the resulting region still
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* covers [_stext, _etext], and that all relative branches can
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* be resolved without veneers.
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*/
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module_range = MODULES_VSIZE - (u64)(_etext - _stext);
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module_alloc_base = (u64)_etext + offset - MODULES_VSIZE;
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}
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/* use the lower 21 bits to randomize the base of the module region */
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module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21;
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module_alloc_base &= PAGE_MASK;
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__flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base));
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__flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed));
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return offset;
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}
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