94 lines
2.7 KiB
C
94 lines
2.7 KiB
C
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// 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 <linux/pgtable.h>
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#include <linux/random.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/sections.h>
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#include <asm/setup.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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struct arm64_ftr_override kaslr_feature_override __initdata;
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static int __init kaslr_init(void)
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{
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u64 module_range;
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u32 seed;
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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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if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) {
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pr_info("KASLR disabled on command line\n");
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return 0;
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}
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if (!kaslr_enabled()) {
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pr_warn("KASLR disabled due to lack of seed\n");
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return 0;
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}
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pr_info("KASLR enabled\n");
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/*
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* KASAN without KASAN_VMALLOC does not expect the module region to
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* intersect the vmalloc region, since shadow memory is allocated for
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* each module at load time, whereas the vmalloc region will already be
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* shadowed by KASAN zero pages.
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*/
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BUILD_BUG_ON((IS_ENABLED(CONFIG_KASAN_GENERIC) ||
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IS_ENABLED(CONFIG_KASAN_SW_TAGS)) &&
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!IS_ENABLED(CONFIG_KASAN_VMALLOC));
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seed = get_random_u32();
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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 - SZ_2G, (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 unless this region is exhausted
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* and we fall back to a larger 2GB window in module_alloc()
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* when ARM64_MODULE_PLTS is enabled.
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*/
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module_range = MODULES_VSIZE - (u64)(_etext - _stext);
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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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return 0;
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}
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subsys_initcall(kaslr_init)
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