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 */
19u32 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 */
58static 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 */
104efi_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, 0, EFI_ALLOC_LIMIT);
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			   (unsigned long)_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}
160