diff options
Diffstat (limited to 'arch/arm64/kernel/kaslr.c')
| -rw-r--r-- | arch/arm64/kernel/kaslr.c | 185 |
1 files changed, 22 insertions, 163 deletions
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c index a9710efb8c01..c9503ed45a6c 100644 --- a/arch/arm64/kernel/kaslr.c +++ b/arch/arm64/kernel/kaslr.c @@ -1,182 +1,41 @@ +// SPDX-License-Identifier: GPL-2.0-only /* * 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 <linux/printk.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> -u64 __ro_after_init module_alloc_base; -u16 __initdata memstart_offset_seed; +bool __ro_after_init __kaslr_is_enabled = false; -static __init u64 get_kaslr_seed(void *fdt) +void __init kaslr_init(void) { - 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 *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; + if (kaslr_disabled_cmdline()) { + pr_info("KASLR disabled on command line\n"); + return; } -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, u64 modulo_offset) -{ - 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; /* - * 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() + * 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. */ - 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 = 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 - * lower half of the VMALLOC area (VA_BITS - 2). - * 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 = seed & mask; - - /* use the top 16 bits to randomize the linear region */ - memstart_offset_seed = seed >> 48; - - /* - * The kernel Image should not extend across a 1GB/32MB/512MB alignment - * boundary (for 4KB/16KB/64KB granule kernels, respectively). If this - * happens, increase the KASLR offset by the size of the kernel image - * rounded up by SWAPPER_BLOCK_SIZE. - */ - if ((((u64)_text + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT) != - (((u64)_end + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT)) { - u64 kimg_sz = _end - _text; - offset = (offset + round_up(kimg_sz, SWAPPER_BLOCK_SIZE)) - & mask; + if (kaslr_offset() < MIN_KIMG_ALIGN) { + pr_warn("KASLR disabled due to lack of seed\n"); + return; } - 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. - */ - return offset; - - if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { - /* - * Randomize the module region independently from the core - * kernel. This prevents modules from leaking any 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 = VMALLOC_END - VMALLOC_START - MODULES_VSIZE; - module_alloc_base = VMALLOC_START; - } 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; + pr_info("KASLR enabled\n"); + __kaslr_is_enabled = true; +} - return offset; +static int __init parse_nokaslr(char *unused) +{ + /* nokaslr param handling is done by early cpufeature code */ + return 0; } +early_param("nokaslr", parse_nokaslr); |