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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org>
*/
#include <linux/cache.h>
#include <linux/crc32.h>
#include <linux/init.h>
#include <linux/libfdt.h>
#include <linux/mm_types.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/pgtable.h>
#include <linux/random.h>
#include <asm/fixmap.h>
#include <asm/kernel-pgtable.h>
#include <asm/memory.h>
#include <asm/mmu.h>
#include <asm/sections.h>
#include <asm/setup.h>
u64 __ro_after_init module_alloc_base;
u16 __initdata memstart_offset_seed;
struct arm64_ftr_override kaslr_feature_override __initdata;
static int __init kaslr_init(void)
{
u64 module_range;
u32 seed;
/*
* Set a reasonable default for module_alloc_base in case
* we end up running with module randomization disabled.
*/
module_alloc_base = (u64)_etext - MODULES_VSIZE;
if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) {
pr_info("KASLR disabled on command line\n");
return 0;
}
if (!kaslr_offset()) {
pr_warn("KASLR disabled due to lack of seed\n");
return 0;
}
pr_info("KASLR enabled\n");
/*
* KASAN without KASAN_VMALLOC does not expect the module region to
* intersect the vmalloc region, since shadow memory is allocated for
* each module at load time, whereas the vmalloc region will already be
* shadowed by KASAN zero pages.
*/
BUILD_BUG_ON((IS_ENABLED(CONFIG_KASAN_GENERIC) ||
IS_ENABLED(CONFIG_KASAN_SW_TAGS)) &&
!IS_ENABLED(CONFIG_KASAN_VMALLOC));
seed = get_random_u32();
if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {
/*
* Randomize the module region over a 2 GB window covering the
* kernel. This reduces the risk of modules leaking information
* about the address of the kernel itself, but results in
* branches between modules and the core kernel that are
* resolved via PLTs. (Branches between modules will be
* resolved normally.)
*/
module_range = SZ_2G - (u64)(_end - _stext);
module_alloc_base = max((u64)_end - SZ_2G, (u64)MODULES_VADDR);
} else {
/*
* Randomize the module region by setting module_alloc_base to
* a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE,
* _stext) . This guarantees that the resulting region still
* covers [_stext, _etext], and that all relative branches can
* be resolved without veneers unless this region is exhausted
* and we fall back to a larger 2GB window in module_alloc()
* when ARM64_MODULE_PLTS is enabled.
*/
module_range = MODULES_VSIZE - (u64)(_etext - _stext);
}
/* use the lower 21 bits to randomize the base of the module region */
module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21;
module_alloc_base &= PAGE_MASK;
return 0;
}
subsys_initcall(kaslr_init)
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