1 // SPDX-License-Identifier: GPL-2.0-only
2 //
3 // Copyright (C) 2019 Jason Yan <yanaijie@huawei.com>
4 
5 #include <linux/kernel.h>
6 #include <linux/errno.h>
7 #include <linux/string.h>
8 #include <linux/types.h>
9 #include <linux/mm.h>
10 #include <linux/swap.h>
11 #include <linux/stddef.h>
12 #include <linux/init.h>
13 #include <linux/delay.h>
14 #include <linux/memblock.h>
15 #include <linux/libfdt.h>
16 #include <linux/crash_core.h>
17 #include <linux/of.h>
18 #include <linux/of_fdt.h>
19 #include <asm/cacheflush.h>
20 #include <asm/kdump.h>
21 #include <mm/mmu_decl.h>
22 #include <generated/utsrelease.h>
23 
24 struct regions {
25 	unsigned long pa_start;
26 	unsigned long pa_end;
27 	unsigned long kernel_size;
28 	unsigned long dtb_start;
29 	unsigned long dtb_end;
30 	unsigned long initrd_start;
31 	unsigned long initrd_end;
32 	unsigned long crash_start;
33 	unsigned long crash_end;
34 	int reserved_mem;
35 	int reserved_mem_addr_cells;
36 	int reserved_mem_size_cells;
37 };
38 
39 struct regions __initdata regions;
40 
41 static __init void kaslr_get_cmdline(void *fdt)
42 {
43 	early_init_dt_scan_chosen(boot_command_line);
44 }
45 
46 static unsigned long __init rotate_xor(unsigned long hash, const void *area,
47 				       size_t size)
48 {
49 	size_t i;
50 	const unsigned long *ptr = area;
51 
52 	for (i = 0; i < size / sizeof(hash); i++) {
53 		/* Rotate by odd number of bits and XOR. */
54 		hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
55 		hash ^= ptr[i];
56 	}
57 
58 	return hash;
59 }
60 
61 /* Attempt to create a simple starting entropy. This can make it defferent for
62  * every build but it is still not enough. Stronger entropy should
63  * be added to make it change for every boot.
64  */
65 static unsigned long __init get_boot_seed(void *fdt)
66 {
67 	unsigned long hash = 0;
68 
69 	/* build-specific string for starting entropy. */
70 	hash = rotate_xor(hash, linux_banner, strlen(linux_banner));
71 	hash = rotate_xor(hash, fdt, fdt_totalsize(fdt));
72 
73 	return hash;
74 }
75 
76 static __init u64 get_kaslr_seed(void *fdt)
77 {
78 	int node, len;
79 	fdt64_t *prop;
80 	u64 ret;
81 
82 	node = fdt_path_offset(fdt, "/chosen");
83 	if (node < 0)
84 		return 0;
85 
86 	prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
87 	if (!prop || len != sizeof(u64))
88 		return 0;
89 
90 	ret = fdt64_to_cpu(*prop);
91 	*prop = 0;
92 	return ret;
93 }
94 
95 static __init bool regions_overlap(u32 s1, u32 e1, u32 s2, u32 e2)
96 {
97 	return e1 >= s2 && e2 >= s1;
98 }
99 
100 static __init bool overlaps_reserved_region(const void *fdt, u32 start,
101 					    u32 end)
102 {
103 	int subnode, len, i;
104 	u64 base, size;
105 
106 	/* check for overlap with /memreserve/ entries */
107 	for (i = 0; i < fdt_num_mem_rsv(fdt); i++) {
108 		if (fdt_get_mem_rsv(fdt, i, &base, &size) < 0)
109 			continue;
110 		if (regions_overlap(start, end, base, base + size))
111 			return true;
112 	}
113 
114 	if (regions.reserved_mem < 0)
115 		return false;
116 
117 	/* check for overlap with static reservations in /reserved-memory */
118 	for (subnode = fdt_first_subnode(fdt, regions.reserved_mem);
119 	     subnode >= 0;
120 	     subnode = fdt_next_subnode(fdt, subnode)) {
121 		const fdt32_t *reg;
122 		u64 rsv_end;
123 
124 		len = 0;
125 		reg = fdt_getprop(fdt, subnode, "reg", &len);
126 		while (len >= (regions.reserved_mem_addr_cells +
127 			       regions.reserved_mem_size_cells)) {
128 			base = fdt32_to_cpu(reg[0]);
129 			if (regions.reserved_mem_addr_cells == 2)
130 				base = (base << 32) | fdt32_to_cpu(reg[1]);
131 
132 			reg += regions.reserved_mem_addr_cells;
133 			len -= 4 * regions.reserved_mem_addr_cells;
134 
135 			size = fdt32_to_cpu(reg[0]);
136 			if (regions.reserved_mem_size_cells == 2)
137 				size = (size << 32) | fdt32_to_cpu(reg[1]);
138 
139 			reg += regions.reserved_mem_size_cells;
140 			len -= 4 * regions.reserved_mem_size_cells;
141 
142 			if (base >= regions.pa_end)
143 				continue;
144 
145 			rsv_end = min(base + size, (u64)U32_MAX);
146 
147 			if (regions_overlap(start, end, base, rsv_end))
148 				return true;
149 		}
150 	}
151 	return false;
152 }
153 
154 static __init bool overlaps_region(const void *fdt, u32 start,
155 				   u32 end)
156 {
157 	if (regions_overlap(start, end, __pa(_stext), __pa(_end)))
158 		return true;
159 
160 	if (regions_overlap(start, end, regions.dtb_start,
161 			    regions.dtb_end))
162 		return true;
163 
164 	if (regions_overlap(start, end, regions.initrd_start,
165 			    regions.initrd_end))
166 		return true;
167 
168 	if (regions_overlap(start, end, regions.crash_start,
169 			    regions.crash_end))
170 		return true;
171 
172 	return overlaps_reserved_region(fdt, start, end);
173 }
174 
175 static void __init get_crash_kernel(void *fdt, unsigned long size)
176 {
177 #ifdef CONFIG_CRASH_CORE
178 	unsigned long long crash_size, crash_base;
179 	int ret;
180 
181 	ret = parse_crashkernel(boot_command_line, size, &crash_size,
182 				&crash_base);
183 	if (ret != 0 || crash_size == 0)
184 		return;
185 	if (crash_base == 0)
186 		crash_base = KDUMP_KERNELBASE;
187 
188 	regions.crash_start = (unsigned long)crash_base;
189 	regions.crash_end = (unsigned long)(crash_base + crash_size);
190 
191 	pr_debug("crash_base=0x%llx crash_size=0x%llx\n", crash_base, crash_size);
192 #endif
193 }
194 
195 static void __init get_initrd_range(void *fdt)
196 {
197 	u64 start, end;
198 	int node, len;
199 	const __be32 *prop;
200 
201 	node = fdt_path_offset(fdt, "/chosen");
202 	if (node < 0)
203 		return;
204 
205 	prop = fdt_getprop(fdt, node, "linux,initrd-start", &len);
206 	if (!prop)
207 		return;
208 	start = of_read_number(prop, len / 4);
209 
210 	prop = fdt_getprop(fdt, node, "linux,initrd-end", &len);
211 	if (!prop)
212 		return;
213 	end = of_read_number(prop, len / 4);
214 
215 	regions.initrd_start = (unsigned long)start;
216 	regions.initrd_end = (unsigned long)end;
217 
218 	pr_debug("initrd_start=0x%llx  initrd_end=0x%llx\n", start, end);
219 }
220 
221 static __init unsigned long get_usable_address(const void *fdt,
222 					       unsigned long start,
223 					       unsigned long offset)
224 {
225 	unsigned long pa;
226 	unsigned long pa_end;
227 
228 	for (pa = offset; (long)pa > (long)start; pa -= SZ_16K) {
229 		pa_end = pa + regions.kernel_size;
230 		if (overlaps_region(fdt, pa, pa_end))
231 			continue;
232 
233 		return pa;
234 	}
235 	return 0;
236 }
237 
238 static __init void get_cell_sizes(const void *fdt, int node, int *addr_cells,
239 				  int *size_cells)
240 {
241 	const int *prop;
242 	int len;
243 
244 	/*
245 	 * Retrieve the #address-cells and #size-cells properties
246 	 * from the 'node', or use the default if not provided.
247 	 */
248 	*addr_cells = *size_cells = 1;
249 
250 	prop = fdt_getprop(fdt, node, "#address-cells", &len);
251 	if (len == 4)
252 		*addr_cells = fdt32_to_cpu(*prop);
253 	prop = fdt_getprop(fdt, node, "#size-cells", &len);
254 	if (len == 4)
255 		*size_cells = fdt32_to_cpu(*prop);
256 }
257 
258 static unsigned long __init kaslr_legal_offset(void *dt_ptr, unsigned long index,
259 					       unsigned long offset)
260 {
261 	unsigned long koffset = 0;
262 	unsigned long start;
263 
264 	while ((long)index >= 0) {
265 		offset = memstart_addr + index * SZ_64M + offset;
266 		start = memstart_addr + index * SZ_64M;
267 		koffset = get_usable_address(dt_ptr, start, offset);
268 		if (koffset)
269 			break;
270 		index--;
271 	}
272 
273 	if (koffset != 0)
274 		koffset -= memstart_addr;
275 
276 	return koffset;
277 }
278 
279 static inline __init bool kaslr_disabled(void)
280 {
281 	return strstr(boot_command_line, "nokaslr") != NULL;
282 }
283 
284 static unsigned long __init kaslr_choose_location(void *dt_ptr, phys_addr_t size,
285 						  unsigned long kernel_sz)
286 {
287 	unsigned long offset, random;
288 	unsigned long ram, linear_sz;
289 	u64 seed;
290 	unsigned long index;
291 
292 	kaslr_get_cmdline(dt_ptr);
293 	if (kaslr_disabled())
294 		return 0;
295 
296 	random = get_boot_seed(dt_ptr);
297 
298 	seed = get_tb() << 32;
299 	seed ^= get_tb();
300 	random = rotate_xor(random, &seed, sizeof(seed));
301 
302 	/*
303 	 * Retrieve (and wipe) the seed from the FDT
304 	 */
305 	seed = get_kaslr_seed(dt_ptr);
306 	if (seed)
307 		random = rotate_xor(random, &seed, sizeof(seed));
308 	else
309 		pr_warn("KASLR: No safe seed for randomizing the kernel base.\n");
310 
311 	ram = min_t(phys_addr_t, __max_low_memory, size);
312 	ram = map_mem_in_cams(ram, CONFIG_LOWMEM_CAM_NUM, true, true);
313 	linear_sz = min_t(unsigned long, ram, SZ_512M);
314 
315 	/* If the linear size is smaller than 64M, do not randomize */
316 	if (linear_sz < SZ_64M)
317 		return 0;
318 
319 	/* check for a reserved-memory node and record its cell sizes */
320 	regions.reserved_mem = fdt_path_offset(dt_ptr, "/reserved-memory");
321 	if (regions.reserved_mem >= 0)
322 		get_cell_sizes(dt_ptr, regions.reserved_mem,
323 			       &regions.reserved_mem_addr_cells,
324 			       &regions.reserved_mem_size_cells);
325 
326 	regions.pa_start = memstart_addr;
327 	regions.pa_end = memstart_addr + linear_sz;
328 	regions.dtb_start = __pa(dt_ptr);
329 	regions.dtb_end = __pa(dt_ptr) + fdt_totalsize(dt_ptr);
330 	regions.kernel_size = kernel_sz;
331 
332 	get_initrd_range(dt_ptr);
333 	get_crash_kernel(dt_ptr, ram);
334 
335 	/*
336 	 * Decide which 64M we want to start
337 	 * Only use the low 8 bits of the random seed
338 	 */
339 	index = random & 0xFF;
340 	index %= linear_sz / SZ_64M;
341 
342 	/* Decide offset inside 64M */
343 	offset = random % (SZ_64M - kernel_sz);
344 	offset = round_down(offset, SZ_16K);
345 
346 	return kaslr_legal_offset(dt_ptr, index, offset);
347 }
348 
349 /*
350  * To see if we need to relocate the kernel to a random offset
351  * void *dt_ptr - address of the device tree
352  * phys_addr_t size - size of the first memory block
353  */
354 notrace void __init kaslr_early_init(void *dt_ptr, phys_addr_t size)
355 {
356 	unsigned long tlb_virt;
357 	phys_addr_t tlb_phys;
358 	unsigned long offset;
359 	unsigned long kernel_sz;
360 
361 	kernel_sz = (unsigned long)_end - (unsigned long)_stext;
362 
363 	offset = kaslr_choose_location(dt_ptr, size, kernel_sz);
364 	if (offset == 0)
365 		return;
366 
367 	kernstart_virt_addr += offset;
368 	kernstart_addr += offset;
369 
370 	is_second_reloc = 1;
371 
372 	if (offset >= SZ_64M) {
373 		tlb_virt = round_down(kernstart_virt_addr, SZ_64M);
374 		tlb_phys = round_down(kernstart_addr, SZ_64M);
375 
376 		/* Create kernel map to relocate in */
377 		create_kaslr_tlb_entry(1, tlb_virt, tlb_phys);
378 	}
379 
380 	/* Copy the kernel to it's new location and run */
381 	memcpy((void *)kernstart_virt_addr, (void *)_stext, kernel_sz);
382 	flush_icache_range(kernstart_virt_addr, kernstart_virt_addr + kernel_sz);
383 
384 	reloc_kernel_entry(dt_ptr, kernstart_virt_addr);
385 }
386 
387 void __init kaslr_late_init(void)
388 {
389 	/* If randomized, clear the original kernel */
390 	if (kernstart_virt_addr != KERNELBASE) {
391 		unsigned long kernel_sz;
392 
393 		kernel_sz = (unsigned long)_end - kernstart_virt_addr;
394 		memzero_explicit((void *)KERNELBASE, kernel_sz);
395 	}
396 }
397