diff options
Diffstat (limited to 'arch/arm64/kernel/kaslr.c')
-rw-r--r-- | arch/arm64/kernel/kaslr.c | 203 |
1 files changed, 20 insertions, 183 deletions
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c index 2a11a962e571..12c7f3c8ba76 100644 --- a/arch/arm64/kernel/kaslr.c +++ b/arch/arm64/kernel/kaslr.c @@ -4,205 +4,42 @@ */ #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/printk.h> -#include <asm/cacheflush.h> -#include <asm/fixmap.h> -#include <asm/kernel-pgtable.h> +#include <asm/cpufeature.h> #include <asm/memory.h> -#include <asm/mmu.h> -#include <asm/pgtable.h> -#include <asm/sections.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; -} +bool __ro_after_init __kaslr_is_enabled = false; -static __init const u8 *kaslr_get_cmdline(void *fdt) +void __init kaslr_init(void) { - 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; -} - -/* - * 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) { - 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. - */ - cmdline = kaslr_get_cmdline(fdt); - str = strstr(cmdline, "nokaslr"); - if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) { - kaslr_status = KASLR_DISABLED_CMDLINE; - return 0; - } - - if (!seed) { - kaslr_status = KASLR_DISABLED_NO_SEED; - return 0; + if (cpuid_feature_extract_unsigned_field(arm64_sw_feature_override.val & + arm64_sw_feature_override.mask, + ARM64_SW_FEATURE_OVERRIDE_NOKASLR)) { + pr_info("KASLR disabled on command line\n"); + return; } /* - * 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 + * The KASLR offset modulo MIN_KIMG_ALIGN is taken from the physical + * placement of the image rather than from the seed, so a displacement + * of less than MIN_KIMG_ALIGN means that no seed was provided. */ - 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)) - /* - * 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; + if (kaslr_offset() < MIN_KIMG_ALIGN) { + pr_warn("KASLR disabled due to lack of seed\n"); + return; } - /* 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; + pr_info("KASLR enabled\n"); + __kaslr_is_enabled = true; } -static int __init kaslr_init(void) +static int __init parse_nokaslr(char *unused) { - 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; - } - + /* nokaslr param handling is done by early cpufeature code */ return 0; } -core_initcall(kaslr_init) +early_param("nokaslr", parse_nokaslr); |