diff options
Diffstat (limited to 'arch/arm64/kernel/kaslr.c')
| -rw-r--r-- | arch/arm64/kernel/kaslr.c | 178 |
1 files changed, 178 insertions, 0 deletions
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c new file mode 100644 index 000000000..06941c1fe --- /dev/null +++ b/arch/arm64/kernel/kaslr.c @@ -0,0 +1,178 @@ +/* + * Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ + +#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 <asm/cacheflush.h> +#include <asm/fixmap.h> +#include <asm/kernel-pgtable.h> +#include <asm/memory.h> +#include <asm/mmu.h> +#include <asm/pgtable.h> +#include <asm/sections.h> + +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; +} + +static __init const u8 *kaslr_get_cmdline(void *fdt) +{ + static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE; + + if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { + int node; + const u8 *prop; + + node = fdt_path_offset(fdt, "/chosen"); + if (node < 0) + goto out; + + prop = fdt_getprop(fdt, node, "bootargs", NULL); + if (!prop) + goto out; + return prop; + } +out: + return default_cmdline; +} + +extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size, + pgprot_t prot); + +/* + * 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(u64 dt_phys) +{ + void *fdt; + u64 seed, offset, mask, module_range; + const u8 *cmdline, *str; + int size; + + /* + * 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() + */ + early_fixmap_init(); + fdt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL); + if (!fdt) + return 0; + + /* + * Retrieve (and wipe) the seed from the FDT + */ + seed = get_kaslr_seed(fdt); + if (!seed) + return 0; + + /* + * Check if 'nokaslr' appears on the command line, and + * return 0 if that is the case. + */ + cmdline = kaslr_get_cmdline(fdt); + str = strstr(cmdline, "nokaslr"); + if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) + 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 - 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 - 2)) - 1) & ~(SZ_2M - 1); + offset = BIT(VA_BITS - 3) + (seed & mask); + + /* use the top 16 bits to randomize the linear region */ + memstart_offset_seed = seed >> 48; + + if (IS_ENABLED(CONFIG_KASAN)) + /* + * KASAN 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, 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; +} |