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 <asm/cacheflush.h>
18 #include <asm/prom.h>
19 #include <asm/kdump.h>
20 #include <mm/mmu_decl.h>
21 #include <generated/compile.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 /* Simplified build-specific string for starting entropy. */
40 static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
41 		LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
42 
43 struct regions __initdata regions;
44 
45 static __init void kaslr_get_cmdline(void *fdt)
46 {
47 	early_init_dt_scan_chosen(boot_command_line);
48 }
49 
50 static unsigned long __init rotate_xor(unsigned long hash, const void *area,
51 				       size_t size)
52 {
53 	size_t i;
54 	const unsigned long *ptr = area;
55 
56 	for (i = 0; i < size / sizeof(hash); i++) {
57 		/* Rotate by odd number of bits and XOR. */
58 		hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
59 		hash ^= ptr[i];
60 	}
61 
62 	return hash;
63 }
64 
65 /* Attempt to create a simple starting entropy. This can make it defferent for
66  * every build but it is still not enough. Stronger entropy should
67  * be added to make it change for every boot.
68  */
69 static unsigned long __init get_boot_seed(void *fdt)
70 {
71 	unsigned long hash = 0;
72 
73 	hash = rotate_xor(hash, build_str, sizeof(build_str));
74 	hash = rotate_xor(hash, fdt, fdt_totalsize(fdt));
75 
76 	return hash;
77 }
78 
79 static __init u64 get_kaslr_seed(void *fdt)
80 {
81 	int node, len;
82 	fdt64_t *prop;
83 	u64 ret;
84 
85 	node = fdt_path_offset(fdt, "/chosen");
86 	if (node < 0)
87 		return 0;
88 
89 	prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
90 	if (!prop || len != sizeof(u64))
91 		return 0;
92 
93 	ret = fdt64_to_cpu(*prop);
94 	*prop = 0;
95 	return ret;
96 }
97 
98 static __init bool regions_overlap(u32 s1, u32 e1, u32 s2, u32 e2)
99 {
100 	return e1 >= s2 && e2 >= s1;
101 }
102 
103 static __init bool overlaps_reserved_region(const void *fdt, u32 start,
104 					    u32 end)
105 {
106 	int subnode, len, i;
107 	u64 base, size;
108 
109 	/* check for overlap with /memreserve/ entries */
110 	for (i = 0; i < fdt_num_mem_rsv(fdt); i++) {
111 		if (fdt_get_mem_rsv(fdt, i, &base, &size) < 0)
112 			continue;
113 		if (regions_overlap(start, end, base, base + size))
114 			return true;
115 	}
116 
117 	if (regions.reserved_mem < 0)
118 		return false;
119 
120 	/* check for overlap with static reservations in /reserved-memory */
121 	for (subnode = fdt_first_subnode(fdt, regions.reserved_mem);
122 	     subnode >= 0;
123 	     subnode = fdt_next_subnode(fdt, subnode)) {
124 		const fdt32_t *reg;
125 		u64 rsv_end;
126 
127 		len = 0;
128 		reg = fdt_getprop(fdt, subnode, "reg", &len);
129 		while (len >= (regions.reserved_mem_addr_cells +
130 			       regions.reserved_mem_size_cells)) {
131 			base = fdt32_to_cpu(reg[0]);
132 			if (regions.reserved_mem_addr_cells == 2)
133 				base = (base << 32) | fdt32_to_cpu(reg[1]);
134 
135 			reg += regions.reserved_mem_addr_cells;
136 			len -= 4 * regions.reserved_mem_addr_cells;
137 
138 			size = fdt32_to_cpu(reg[0]);
139 			if (regions.reserved_mem_size_cells == 2)
140 				size = (size << 32) | fdt32_to_cpu(reg[1]);
141 
142 			reg += regions.reserved_mem_size_cells;
143 			len -= 4 * regions.reserved_mem_size_cells;
144 
145 			if (base >= regions.pa_end)
146 				continue;
147 
148 			rsv_end = min(base + size, (u64)U32_MAX);
149 
150 			if (regions_overlap(start, end, base, rsv_end))
151 				return true;
152 		}
153 	}
154 	return false;
155 }
156 
157 static __init bool overlaps_region(const void *fdt, u32 start,
158 				   u32 end)
159 {
160 	if (regions_overlap(start, end, __pa(_stext), __pa(_end)))
161 		return true;
162 
163 	if (regions_overlap(start, end, regions.dtb_start,
164 			    regions.dtb_end))
165 		return true;
166 
167 	if (regions_overlap(start, end, regions.initrd_start,
168 			    regions.initrd_end))
169 		return true;
170 
171 	if (regions_overlap(start, end, regions.crash_start,
172 			    regions.crash_end))
173 		return true;
174 
175 	return overlaps_reserved_region(fdt, start, end);
176 }
177 
178 static void __init get_crash_kernel(void *fdt, unsigned long size)
179 {
180 #ifdef CONFIG_CRASH_CORE
181 	unsigned long long crash_size, crash_base;
182 	int ret;
183 
184 	ret = parse_crashkernel(boot_command_line, size, &crash_size,
185 				&crash_base);
186 	if (ret != 0 || crash_size == 0)
187 		return;
188 	if (crash_base == 0)
189 		crash_base = KDUMP_KERNELBASE;
190 
191 	regions.crash_start = (unsigned long)crash_base;
192 	regions.crash_end = (unsigned long)(crash_base + crash_size);
193 
194 	pr_debug("crash_base=0x%llx crash_size=0x%llx\n", crash_base, crash_size);
195 #endif
196 }
197 
198 static void __init get_initrd_range(void *fdt)
199 {
200 	u64 start, end;
201 	int node, len;
202 	const __be32 *prop;
203 
204 	node = fdt_path_offset(fdt, "/chosen");
205 	if (node < 0)
206 		return;
207 
208 	prop = fdt_getprop(fdt, node, "linux,initrd-start", &len);
209 	if (!prop)
210 		return;
211 	start = of_read_number(prop, len / 4);
212 
213 	prop = fdt_getprop(fdt, node, "linux,initrd-end", &len);
214 	if (!prop)
215 		return;
216 	end = of_read_number(prop, len / 4);
217 
218 	regions.initrd_start = (unsigned long)start;
219 	regions.initrd_end = (unsigned long)end;
220 
221 	pr_debug("initrd_start=0x%llx  initrd_end=0x%llx\n", start, end);
222 }
223 
224 static __init unsigned long get_usable_address(const void *fdt,
225 					       unsigned long start,
226 					       unsigned long offset)
227 {
228 	unsigned long pa;
229 	unsigned long pa_end;
230 
231 	for (pa = offset; (long)pa > (long)start; pa -= SZ_16K) {
232 		pa_end = pa + regions.kernel_size;
233 		if (overlaps_region(fdt, pa, pa_end))
234 			continue;
235 
236 		return pa;
237 	}
238 	return 0;
239 }
240 
241 static __init void get_cell_sizes(const void *fdt, int node, int *addr_cells,
242 				  int *size_cells)
243 {
244 	const int *prop;
245 	int len;
246 
247 	/*
248 	 * Retrieve the #address-cells and #size-cells properties
249 	 * from the 'node', or use the default if not provided.
250 	 */
251 	*addr_cells = *size_cells = 1;
252 
253 	prop = fdt_getprop(fdt, node, "#address-cells", &len);
254 	if (len == 4)
255 		*addr_cells = fdt32_to_cpu(*prop);
256 	prop = fdt_getprop(fdt, node, "#size-cells", &len);
257 	if (len == 4)
258 		*size_cells = fdt32_to_cpu(*prop);
259 }
260 
261 static unsigned long __init kaslr_legal_offset(void *dt_ptr, unsigned long index,
262 					       unsigned long offset)
263 {
264 	unsigned long koffset = 0;
265 	unsigned long start;
266 
267 	while ((long)index >= 0) {
268 		offset = memstart_addr + index * SZ_64M + offset;
269 		start = memstart_addr + index * SZ_64M;
270 		koffset = get_usable_address(dt_ptr, start, offset);
271 		if (koffset)
272 			break;
273 		index--;
274 	}
275 
276 	if (koffset != 0)
277 		koffset -= memstart_addr;
278 
279 	return koffset;
280 }
281 
282 static inline __init bool kaslr_disabled(void)
283 {
284 	return strstr(boot_command_line, "nokaslr") != NULL;
285 }
286 
287 static unsigned long __init kaslr_choose_location(void *dt_ptr, phys_addr_t size,
288 						  unsigned long kernel_sz)
289 {
290 	unsigned long offset, random;
291 	unsigned long ram, linear_sz;
292 	u64 seed;
293 	unsigned long index;
294 
295 	kaslr_get_cmdline(dt_ptr);
296 	if (kaslr_disabled())
297 		return 0;
298 
299 	random = get_boot_seed(dt_ptr);
300 
301 	seed = get_tb() << 32;
302 	seed ^= get_tb();
303 	random = rotate_xor(random, &seed, sizeof(seed));
304 
305 	/*
306 	 * Retrieve (and wipe) the seed from the FDT
307 	 */
308 	seed = get_kaslr_seed(dt_ptr);
309 	if (seed)
310 		random = rotate_xor(random, &seed, sizeof(seed));
311 	else
312 		pr_warn("KASLR: No safe seed for randomizing the kernel base.\n");
313 
314 	ram = min_t(phys_addr_t, __max_low_memory, size);
315 	ram = map_mem_in_cams(ram, CONFIG_LOWMEM_CAM_NUM, true, true);
316 	linear_sz = min_t(unsigned long, ram, SZ_512M);
317 
318 	/* If the linear size is smaller than 64M, do not randmize */
319 	if (linear_sz < SZ_64M)
320 		return 0;
321 
322 	/* check for a reserved-memory node and record its cell sizes */
323 	regions.reserved_mem = fdt_path_offset(dt_ptr, "/reserved-memory");
324 	if (regions.reserved_mem >= 0)
325 		get_cell_sizes(dt_ptr, regions.reserved_mem,
326 			       &regions.reserved_mem_addr_cells,
327 			       &regions.reserved_mem_size_cells);
328 
329 	regions.pa_start = memstart_addr;
330 	regions.pa_end = memstart_addr + linear_sz;
331 	regions.dtb_start = __pa(dt_ptr);
332 	regions.dtb_end = __pa(dt_ptr) + fdt_totalsize(dt_ptr);
333 	regions.kernel_size = kernel_sz;
334 
335 	get_initrd_range(dt_ptr);
336 	get_crash_kernel(dt_ptr, ram);
337 
338 	/*
339 	 * Decide which 64M we want to start
340 	 * Only use the low 8 bits of the random seed
341 	 */
342 	index = random & 0xFF;
343 	index %= linear_sz / SZ_64M;
344 
345 	/* Decide offset inside 64M */
346 	offset = random % (SZ_64M - kernel_sz);
347 	offset = round_down(offset, SZ_16K);
348 
349 	return kaslr_legal_offset(dt_ptr, index, offset);
350 }
351 
352 /*
353  * To see if we need to relocate the kernel to a random offset
354  * void *dt_ptr - address of the device tree
355  * phys_addr_t size - size of the first memory block
356  */
357 notrace void __init kaslr_early_init(void *dt_ptr, phys_addr_t size)
358 {
359 	unsigned long tlb_virt;
360 	phys_addr_t tlb_phys;
361 	unsigned long offset;
362 	unsigned long kernel_sz;
363 
364 	kernel_sz = (unsigned long)_end - (unsigned long)_stext;
365 
366 	offset = kaslr_choose_location(dt_ptr, size, kernel_sz);
367 	if (offset == 0)
368 		return;
369 
370 	kernstart_virt_addr += offset;
371 	kernstart_addr += offset;
372 
373 	is_second_reloc = 1;
374 
375 	if (offset >= SZ_64M) {
376 		tlb_virt = round_down(kernstart_virt_addr, SZ_64M);
377 		tlb_phys = round_down(kernstart_addr, SZ_64M);
378 
379 		/* Create kernel map to relocate in */
380 		create_kaslr_tlb_entry(1, tlb_virt, tlb_phys);
381 	}
382 
383 	/* Copy the kernel to it's new location and run */
384 	memcpy((void *)kernstart_virt_addr, (void *)_stext, kernel_sz);
385 	flush_icache_range(kernstart_virt_addr, kernstart_virt_addr + kernel_sz);
386 
387 	reloc_kernel_entry(dt_ptr, kernstart_virt_addr);
388 }
389 
390 void __init kaslr_late_init(void)
391 {
392 	/* If randomized, clear the original kernel */
393 	if (kernstart_virt_addr != KERNELBASE) {
394 		unsigned long kernel_sz;
395 
396 		kernel_sz = (unsigned long)_end - kernstart_virt_addr;
397 		memzero_explicit((void *)KERNELBASE, kernel_sz);
398 	}
399 }
400