diff options
Diffstat (limited to 'drivers/firmware/efi/libstub/kaslr.c')
| -rw-r--r-- | drivers/firmware/efi/libstub/kaslr.c | 159 |
1 files changed, 159 insertions, 0 deletions
diff --git a/drivers/firmware/efi/libstub/kaslr.c b/drivers/firmware/efi/libstub/kaslr.c new file mode 100644 index 000000000000..62d63f7a2645 --- /dev/null +++ b/drivers/firmware/efi/libstub/kaslr.c @@ -0,0 +1,159 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Helper functions used by the EFI stub on multiple + * architectures to deal with physical address space randomization. + */ +#include <linux/efi.h> + +#include "efistub.h" + +/** + * efi_kaslr_get_phys_seed() - Get random seed for physical kernel KASLR + * @image_handle: Handle to the image + * + * If KASLR is not disabled, obtain a random seed using EFI_RNG_PROTOCOL + * that will be used to move the kernel physical mapping. + * + * Return: the random seed + */ +u32 efi_kaslr_get_phys_seed(efi_handle_t image_handle) +{ + efi_status_t status; + u32 phys_seed; + efi_guid_t li_fixed_proto = LINUX_EFI_LOADED_IMAGE_FIXED_GUID; + void *p; + + if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE)) + return 0; + + if (efi_nokaslr) { + efi_info("KASLR disabled on kernel command line\n"); + } else if (efi_bs_call(handle_protocol, image_handle, + &li_fixed_proto, &p) == EFI_SUCCESS) { + efi_info("Image placement fixed by loader\n"); + } else { + status = efi_get_random_bytes(sizeof(phys_seed), + (u8 *)&phys_seed); + if (status == EFI_SUCCESS) { + return phys_seed; + } else if (status == EFI_NOT_FOUND) { + efi_info("EFI_RNG_PROTOCOL unavailable\n"); + efi_nokaslr = true; + } else if (status != EFI_SUCCESS) { + efi_err("efi_get_random_bytes() failed (0x%lx)\n", + status); + efi_nokaslr = true; + } + } + + return 0; +} + +/* + * Distro versions of GRUB may ignore the BSS allocation entirely (i.e., fail + * to provide space, and fail to zero it). Check for this condition by double + * checking that the first and the last byte of the image are covered by the + * same EFI memory map entry. + */ +static bool check_image_region(u64 base, u64 size) +{ + struct efi_boot_memmap *map; + efi_status_t status; + bool ret = false; + int map_offset; + + status = efi_get_memory_map(&map, false); + if (status != EFI_SUCCESS) + return false; + + for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) { + efi_memory_desc_t *md = (void *)map->map + map_offset; + u64 end = md->phys_addr + md->num_pages * EFI_PAGE_SIZE; + + /* + * Find the region that covers base, and return whether + * it covers base+size bytes. + */ + if (base >= md->phys_addr && base < end) { + ret = (base + size) <= end; + break; + } + } + + efi_bs_call(free_pool, map); + + return ret; +} + +/** + * efi_kaslr_relocate_kernel() - Relocate the kernel (random if KASLR enabled) + * @image_addr: Pointer to the current kernel location + * @reserve_addr: Pointer to the relocated kernel location + * @reserve_size: Size of the relocated kernel + * @kernel_size: Size of the text + data + * @kernel_codesize: Size of the text + * @kernel_memsize: Size of the text + data + bss + * @phys_seed: Random seed used for the relocation + * + * If KASLR is not enabled, this function relocates the kernel to a fixed + * address (or leave it as its current location). If KASLR is enabled, the + * kernel physical location is randomized using the seed in parameter. + * + * Return: status code, EFI_SUCCESS if relocation is successful + */ +efi_status_t efi_kaslr_relocate_kernel(unsigned long *image_addr, + unsigned long *reserve_addr, + unsigned long *reserve_size, + unsigned long kernel_size, + unsigned long kernel_codesize, + unsigned long kernel_memsize, + u32 phys_seed) +{ + efi_status_t status; + u64 min_kimg_align = efi_get_kimg_min_align(); + + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && phys_seed != 0) { + /* + * If KASLR is enabled, and we have some randomness available, + * locate the kernel at a randomized offset in physical memory. + */ + status = efi_random_alloc(*reserve_size, min_kimg_align, + reserve_addr, phys_seed, + EFI_LOADER_CODE, EFI_ALLOC_LIMIT); + if (status != EFI_SUCCESS) + efi_warn("efi_random_alloc() failed: 0x%lx\n", status); + } else { + status = EFI_OUT_OF_RESOURCES; + } + + if (status != EFI_SUCCESS) { + if (!check_image_region(*image_addr, kernel_memsize)) { + efi_err("FIRMWARE BUG: Image BSS overlaps adjacent EFI memory region\n"); + } else if (IS_ALIGNED(*image_addr, min_kimg_align) && + (unsigned long)_end < EFI_ALLOC_LIMIT) { + /* + * Just execute from wherever we were loaded by the + * UEFI PE/COFF loader if the placement is suitable. + */ + *reserve_size = 0; + return EFI_SUCCESS; + } + + status = efi_allocate_pages_aligned(*reserve_size, reserve_addr, + ULONG_MAX, min_kimg_align, + EFI_LOADER_CODE); + + if (status != EFI_SUCCESS) { + efi_err("Failed to relocate kernel\n"); + *reserve_size = 0; + return status; + } + } + + memcpy((void *)*reserve_addr, (void *)*image_addr, kernel_size); + *image_addr = *reserve_addr; + efi_icache_sync(*image_addr, *image_addr + kernel_codesize); + efi_remap_image(*image_addr, *reserve_size, kernel_codesize); + + return status; +} |