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| 1 | +// SPDX-License-Identifier: GPL-2.0 |
| 2 | +/* |
| 3 | + * Helper functions used by the EFI stub on multiple |
| 4 | + * architectures to deal with physical address space randomization. |
| 5 | + */ |
| 6 | +#include <linux/efi.h> |
| 7 | + |
| 8 | +#include "efistub.h" |
| 9 | + |
| 10 | +/** |
| 11 | + * efi_kaslr_get_phys_seed() - Get random seed for physical kernel KASLR |
| 12 | + * @image_handle: Handle to the image |
| 13 | + * |
| 14 | + * If KASLR is not disabled, obtain a random seed using EFI_RNG_PROTOCOL |
| 15 | + * that will be used to move the kernel physical mapping. |
| 16 | + * |
| 17 | + * Return: the random seed |
| 18 | + */ |
| 19 | +u32 efi_kaslr_get_phys_seed(efi_handle_t image_handle) |
| 20 | +{ |
| 21 | + efi_status_t status; |
| 22 | + u32 phys_seed; |
| 23 | + efi_guid_t li_fixed_proto = LINUX_EFI_LOADED_IMAGE_FIXED_GUID; |
| 24 | + void *p; |
| 25 | + |
| 26 | + if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE)) |
| 27 | + return 0; |
| 28 | + |
| 29 | + if (efi_nokaslr) { |
| 30 | + efi_info("KASLR disabled on kernel command line\n"); |
| 31 | + } else if (efi_bs_call(handle_protocol, image_handle, |
| 32 | + &li_fixed_proto, &p) == EFI_SUCCESS) { |
| 33 | + efi_info("Image placement fixed by loader\n"); |
| 34 | + } else { |
| 35 | + status = efi_get_random_bytes(sizeof(phys_seed), |
| 36 | + (u8 *)&phys_seed); |
| 37 | + if (status == EFI_SUCCESS) { |
| 38 | + return phys_seed; |
| 39 | + } else if (status == EFI_NOT_FOUND) { |
| 40 | + efi_info("EFI_RNG_PROTOCOL unavailable\n"); |
| 41 | + efi_nokaslr = true; |
| 42 | + } else if (status != EFI_SUCCESS) { |
| 43 | + efi_err("efi_get_random_bytes() failed (0x%lx)\n", |
| 44 | + status); |
| 45 | + efi_nokaslr = true; |
| 46 | + } |
| 47 | + } |
| 48 | + |
| 49 | + return 0; |
| 50 | +} |
| 51 | + |
| 52 | +/* |
| 53 | + * Distro versions of GRUB may ignore the BSS allocation entirely (i.e., fail |
| 54 | + * to provide space, and fail to zero it). Check for this condition by double |
| 55 | + * checking that the first and the last byte of the image are covered by the |
| 56 | + * same EFI memory map entry. |
| 57 | + */ |
| 58 | +static bool check_image_region(u64 base, u64 size) |
| 59 | +{ |
| 60 | + struct efi_boot_memmap *map; |
| 61 | + efi_status_t status; |
| 62 | + bool ret = false; |
| 63 | + int map_offset; |
| 64 | + |
| 65 | + status = efi_get_memory_map(&map, false); |
| 66 | + if (status != EFI_SUCCESS) |
| 67 | + return false; |
| 68 | + |
| 69 | + for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) { |
| 70 | + efi_memory_desc_t *md = (void *)map->map + map_offset; |
| 71 | + u64 end = md->phys_addr + md->num_pages * EFI_PAGE_SIZE; |
| 72 | + |
| 73 | + /* |
| 74 | + * Find the region that covers base, and return whether |
| 75 | + * it covers base+size bytes. |
| 76 | + */ |
| 77 | + if (base >= md->phys_addr && base < end) { |
| 78 | + ret = (base + size) <= end; |
| 79 | + break; |
| 80 | + } |
| 81 | + } |
| 82 | + |
| 83 | + efi_bs_call(free_pool, map); |
| 84 | + |
| 85 | + return ret; |
| 86 | +} |
| 87 | + |
| 88 | +/** |
| 89 | + * efi_kaslr_relocate_kernel() - Relocate the kernel (random if KASLR enabled) |
| 90 | + * @image_addr: Pointer to the current kernel location |
| 91 | + * @reserve_addr: Pointer to the relocated kernel location |
| 92 | + * @reserve_size: Size of the relocated kernel |
| 93 | + * @kernel_size: Size of the text + data |
| 94 | + * @kernel_codesize: Size of the text |
| 95 | + * @kernel_memsize: Size of the text + data + bss |
| 96 | + * @phys_seed: Random seed used for the relocation |
| 97 | + * |
| 98 | + * If KASLR is not enabled, this function relocates the kernel to a fixed |
| 99 | + * address (or leave it as its current location). If KASLR is enabled, the |
| 100 | + * kernel physical location is randomized using the seed in parameter. |
| 101 | + * |
| 102 | + * Return: status code, EFI_SUCCESS if relocation is successful |
| 103 | + */ |
| 104 | +efi_status_t efi_kaslr_relocate_kernel(unsigned long *image_addr, |
| 105 | + unsigned long *reserve_addr, |
| 106 | + unsigned long *reserve_size, |
| 107 | + unsigned long kernel_size, |
| 108 | + unsigned long kernel_codesize, |
| 109 | + unsigned long kernel_memsize, |
| 110 | + u32 phys_seed) |
| 111 | +{ |
| 112 | + efi_status_t status; |
| 113 | + u64 min_kimg_align = efi_get_kimg_min_align(); |
| 114 | + |
| 115 | + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && phys_seed != 0) { |
| 116 | + /* |
| 117 | + * If KASLR is enabled, and we have some randomness available, |
| 118 | + * locate the kernel at a randomized offset in physical memory. |
| 119 | + */ |
| 120 | + status = efi_random_alloc(*reserve_size, min_kimg_align, |
| 121 | + reserve_addr, phys_seed, |
| 122 | + EFI_LOADER_CODE); |
| 123 | + if (status != EFI_SUCCESS) |
| 124 | + efi_warn("efi_random_alloc() failed: 0x%lx\n", status); |
| 125 | + } else { |
| 126 | + status = EFI_OUT_OF_RESOURCES; |
| 127 | + } |
| 128 | + |
| 129 | + if (status != EFI_SUCCESS) { |
| 130 | + if (!check_image_region(*image_addr, kernel_memsize)) { |
| 131 | + efi_err("FIRMWARE BUG: Image BSS overlaps adjacent EFI memory region\n"); |
| 132 | + } else if (IS_ALIGNED(*image_addr, min_kimg_align) && |
| 133 | + (u64)_end < EFI_ALLOC_LIMIT) { |
| 134 | + /* |
| 135 | + * Just execute from wherever we were loaded by the |
| 136 | + * UEFI PE/COFF loader if the placement is suitable. |
| 137 | + */ |
| 138 | + *reserve_size = 0; |
| 139 | + return EFI_SUCCESS; |
| 140 | + } |
| 141 | + |
| 142 | + status = efi_allocate_pages_aligned(*reserve_size, reserve_addr, |
| 143 | + ULONG_MAX, min_kimg_align, |
| 144 | + EFI_LOADER_CODE); |
| 145 | + |
| 146 | + if (status != EFI_SUCCESS) { |
| 147 | + efi_err("Failed to relocate kernel\n"); |
| 148 | + *reserve_size = 0; |
| 149 | + return status; |
| 150 | + } |
| 151 | + } |
| 152 | + |
| 153 | + memcpy((void *)*reserve_addr, (void *)*image_addr, kernel_size); |
| 154 | + *image_addr = *reserve_addr; |
| 155 | + efi_icache_sync(*image_addr, *image_addr + kernel_codesize); |
| 156 | + efi_remap_image(*image_addr, *reserve_size, kernel_codesize); |
| 157 | + |
| 158 | + return status; |
| 159 | +} |
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