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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/cacheflush.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>
- enum kaslr_status {
- KASLR_ENABLED,
- KASLR_DISABLED_CMDLINE,
- KASLR_DISABLED_NO_SEED,
- KASLR_DISABLED_FDT_REMAP,
- };
- static enum kaslr_status __initdata kaslr_status;
- u64 __ro_after_init module_alloc_base;
- u16 __initdata memstart_offset_seed;
- static __init u64 get_kaslr_seed(void *fdt)
- {
- int node, len;
- fdt64_t *prop;
- u64 ret;
- node = fdt_path_offset(fdt, "/chosen");
- if (node < 0)
- return 0;
- prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
- if (!prop || len != sizeof(u64))
- return 0;
- ret = fdt64_to_cpu(*prop);
- *prop = 0;
- return ret;
- }
- struct arm64_ftr_override kaslr_feature_override __initdata;
- /*
- * This routine will be executed with the kernel mapped at its default virtual
- * address, and if it returns successfully, the kernel will be remapped, and
- * start_kernel() will be executed from a randomized virtual offset. The
- * relocation will result in all absolute references (e.g., static variables
- * containing function pointers) to be reinitialized, and zero-initialized
- * .bss variables will be reset to 0.
- */
- u64 __init kaslr_early_init(void)
- {
- void *fdt;
- u64 seed, offset, mask, module_range;
- unsigned long raw;
- /*
- * 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;
- __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base));
- /*
- * Try to map the FDT early. If this fails, we simply bail,
- * and proceed with KASLR disabled. We will make another
- * attempt at mapping the FDT in setup_machine()
- */
- fdt = get_early_fdt_ptr();
- if (!fdt) {
- kaslr_status = KASLR_DISABLED_FDT_REMAP;
- return 0;
- }
- /*
- * Retrieve (and wipe) the seed from the FDT
- */
- seed = get_kaslr_seed(fdt);
- /*
- * Check if 'nokaslr' appears on the command line, and
- * return 0 if that is the case.
- */
- if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) {
- kaslr_status = KASLR_DISABLED_CMDLINE;
- return 0;
- }
- /*
- * Mix in any entropy obtainable architecturally if enabled
- * and supported.
- */
- if (arch_get_random_seed_long_early(&raw))
- seed ^= raw;
- if (!seed) {
- kaslr_status = KASLR_DISABLED_NO_SEED;
- return 0;
- }
- /*
- * OK, so we are proceeding with KASLR enabled. Calculate a suitable
- * kernel image offset from the seed. Let's place the kernel in the
- * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of
- * the lower and upper quarters to avoid colliding with other
- * allocations.
- * Even if we could randomize at page granularity for 16k and 64k pages,
- * let's always round to 2 MB so we don't interfere with the ability to
- * map using contiguous PTEs
- */
- mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1);
- offset = BIT(VA_BITS_MIN - 3) + (seed & mask);
- /* use the top 16 bits to randomize the linear region */
- memstart_offset_seed = seed >> 48;
- if (!IS_ENABLED(CONFIG_KASAN_VMALLOC) &&
- (IS_ENABLED(CONFIG_KASAN_GENERIC) ||
- IS_ENABLED(CONFIG_KASAN_SW_TAGS)))
- /*
- * 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 is shadowed by KASAN zero pages. So keep modules
- * out of the vmalloc region if KASAN is enabled without
- * KASAN_VMALLOC, and put the kernel well within 4 GB of the
- * module region.
- */
- return offset % SZ_2G;
- 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 + offset - 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.
- */
- module_range = MODULES_VSIZE - (u64)(_etext - _stext);
- module_alloc_base = (u64)_etext + offset - MODULES_VSIZE;
- }
- /* 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;
- __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base));
- __flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed));
- return offset;
- }
- static int __init kaslr_init(void)
- {
- switch (kaslr_status) {
- case KASLR_ENABLED:
- pr_info("KASLR enabled\n");
- break;
- case KASLR_DISABLED_CMDLINE:
- pr_info("KASLR disabled on command line\n");
- break;
- case KASLR_DISABLED_NO_SEED:
- pr_warn("KASLR disabled due to lack of seed\n");
- break;
- case KASLR_DISABLED_FDT_REMAP:
- pr_warn("KASLR disabled due to FDT remapping failure\n");
- break;
- }
- return 0;
- }
- core_initcall(kaslr_init)
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