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196 lines
5.5 KiB
196 lines
5.5 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* Copyright (C) 2016 Linaro Ltd <[email protected]> |
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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/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/sections.h> |
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#include <asm/setup.h> |
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enum kaslr_status { |
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KASLR_ENABLED, |
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KASLR_DISABLED_CMDLINE, |
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KASLR_DISABLED_NO_SEED, |
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KASLR_DISABLED_FDT_REMAP, |
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}; |
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static enum kaslr_status __initdata kaslr_status; |
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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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struct arm64_ftr_override kaslr_feature_override __initdata; |
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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(void) |
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{ |
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void *fdt; |
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u64 seed, offset, mask, module_range; |
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unsigned long raw; |
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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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fdt = get_early_fdt_ptr(); |
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if (!fdt) { |
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kaslr_status = KASLR_DISABLED_FDT_REMAP; |
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return 0; |
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} |
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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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/* |
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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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if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) { |
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kaslr_status = KASLR_DISABLED_CMDLINE; |
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return 0; |
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} |
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/* |
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* Mix in any entropy obtainable architecturally if enabled |
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* and supported. |
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*/ |
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if (arch_get_random_seed_long_early(&raw)) |
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seed ^= raw; |
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if (!seed) { |
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kaslr_status = KASLR_DISABLED_NO_SEED; |
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return 0; |
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} |
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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_GENERIC) || |
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IS_ENABLED(CONFIG_KASAN_SW_TAGS)) |
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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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static int __init kaslr_init(void) |
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{ |
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switch (kaslr_status) { |
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case KASLR_ENABLED: |
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pr_info("KASLR enabled\n"); |
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break; |
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case KASLR_DISABLED_CMDLINE: |
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pr_info("KASLR disabled on command line\n"); |
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break; |
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case KASLR_DISABLED_NO_SEED: |
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pr_warn("KASLR disabled due to lack of seed\n"); |
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break; |
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case KASLR_DISABLED_FDT_REMAP: |
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pr_warn("KASLR disabled due to FDT remapping failure\n"); |
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break; |
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} |
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return 0; |
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} |
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core_initcall(kaslr_init)
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