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8ab3820f KC |
1 | #include "misc.h" |
2 | ||
3 | #ifdef CONFIG_RANDOMIZE_BASE | |
5bfce5ef KC |
4 | #include <asm/msr.h> |
5 | #include <asm/archrandom.h> | |
82fa9637 | 6 | #include <asm/e820.h> |
5bfce5ef | 7 | |
a653f356 KC |
8 | #include <generated/compile.h> |
9 | #include <linux/module.h> | |
10 | #include <linux/uts.h> | |
11 | #include <linux/utsname.h> | |
12 | #include <generated/utsrelease.h> | |
a653f356 KC |
13 | |
14 | /* Simplified build-specific string for starting entropy. */ | |
327f7d72 | 15 | static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@" |
a653f356 KC |
16 | LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION; |
17 | ||
5bfce5ef KC |
18 | #define I8254_PORT_CONTROL 0x43 |
19 | #define I8254_PORT_COUNTER0 0x40 | |
20 | #define I8254_CMD_READBACK 0xC0 | |
21 | #define I8254_SELECT_COUNTER0 0x02 | |
22 | #define I8254_STATUS_NOTREADY 0x40 | |
23 | static inline u16 i8254(void) | |
24 | { | |
25 | u16 status, timer; | |
26 | ||
27 | do { | |
28 | outb(I8254_PORT_CONTROL, | |
29 | I8254_CMD_READBACK | I8254_SELECT_COUNTER0); | |
30 | status = inb(I8254_PORT_COUNTER0); | |
31 | timer = inb(I8254_PORT_COUNTER0); | |
32 | timer |= inb(I8254_PORT_COUNTER0) << 8; | |
33 | } while (status & I8254_STATUS_NOTREADY); | |
34 | ||
35 | return timer; | |
36 | } | |
37 | ||
a653f356 KC |
38 | static unsigned long rotate_xor(unsigned long hash, const void *area, |
39 | size_t size) | |
40 | { | |
41 | size_t i; | |
42 | unsigned long *ptr = (unsigned long *)area; | |
43 | ||
44 | for (i = 0; i < size / sizeof(hash); i++) { | |
45 | /* Rotate by odd number of bits and XOR. */ | |
46 | hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7); | |
47 | hash ^= ptr[i]; | |
48 | } | |
49 | ||
50 | return hash; | |
51 | } | |
52 | ||
53 | /* Attempt to create a simple but unpredictable starting entropy. */ | |
54 | static unsigned long get_random_boot(void) | |
55 | { | |
56 | unsigned long hash = 0; | |
57 | ||
58 | hash = rotate_xor(hash, build_str, sizeof(build_str)); | |
59 | hash = rotate_xor(hash, real_mode, sizeof(*real_mode)); | |
60 | ||
61 | return hash; | |
62 | } | |
63 | ||
5bfce5ef KC |
64 | static unsigned long get_random_long(void) |
65 | { | |
e8236c4d PA |
66 | #ifdef CONFIG_X86_64 |
67 | const unsigned long mix_const = 0x5d6008cbf3848dd3UL; | |
68 | #else | |
69 | const unsigned long mix_const = 0x3f39e593UL; | |
70 | #endif | |
a653f356 KC |
71 | unsigned long raw, random = get_random_boot(); |
72 | bool use_i8254 = true; | |
73 | ||
74 | debug_putstr("KASLR using"); | |
5bfce5ef KC |
75 | |
76 | if (has_cpuflag(X86_FEATURE_RDRAND)) { | |
a653f356 KC |
77 | debug_putstr(" RDRAND"); |
78 | if (rdrand_long(&raw)) { | |
79 | random ^= raw; | |
80 | use_i8254 = false; | |
81 | } | |
5bfce5ef KC |
82 | } |
83 | ||
84 | if (has_cpuflag(X86_FEATURE_TSC)) { | |
a653f356 KC |
85 | debug_putstr(" RDTSC"); |
86 | rdtscll(raw); | |
5bfce5ef | 87 | |
a653f356 KC |
88 | random ^= raw; |
89 | use_i8254 = false; | |
90 | } | |
5bfce5ef | 91 | |
a653f356 KC |
92 | if (use_i8254) { |
93 | debug_putstr(" i8254"); | |
94 | random ^= i8254(); | |
5bfce5ef KC |
95 | } |
96 | ||
e8236c4d PA |
97 | /* Circular multiply for better bit diffusion */ |
98 | asm("mul %3" | |
99 | : "=a" (random), "=d" (raw) | |
100 | : "a" (random), "rm" (mix_const)); | |
101 | random += raw; | |
102 | ||
a653f356 KC |
103 | debug_putstr("...\n"); |
104 | ||
5bfce5ef KC |
105 | return random; |
106 | } | |
8ab3820f | 107 | |
82fa9637 KC |
108 | struct mem_vector { |
109 | unsigned long start; | |
110 | unsigned long size; | |
111 | }; | |
112 | ||
113 | #define MEM_AVOID_MAX 5 | |
114 | struct mem_vector mem_avoid[MEM_AVOID_MAX]; | |
115 | ||
116 | static bool mem_contains(struct mem_vector *region, struct mem_vector *item) | |
117 | { | |
118 | /* Item at least partially before region. */ | |
119 | if (item->start < region->start) | |
120 | return false; | |
121 | /* Item at least partially after region. */ | |
122 | if (item->start + item->size > region->start + region->size) | |
123 | return false; | |
124 | return true; | |
125 | } | |
126 | ||
127 | static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two) | |
128 | { | |
129 | /* Item one is entirely before item two. */ | |
130 | if (one->start + one->size <= two->start) | |
131 | return false; | |
132 | /* Item one is entirely after item two. */ | |
133 | if (one->start >= two->start + two->size) | |
134 | return false; | |
135 | return true; | |
136 | } | |
137 | ||
138 | static void mem_avoid_init(unsigned long input, unsigned long input_size, | |
139 | unsigned long output, unsigned long output_size) | |
140 | { | |
141 | u64 initrd_start, initrd_size; | |
142 | u64 cmd_line, cmd_line_size; | |
143 | unsigned long unsafe, unsafe_len; | |
144 | char *ptr; | |
145 | ||
146 | /* | |
147 | * Avoid the region that is unsafe to overlap during | |
148 | * decompression (see calculations at top of misc.c). | |
149 | */ | |
150 | unsafe_len = (output_size >> 12) + 32768 + 18; | |
151 | unsafe = (unsigned long)input + input_size - unsafe_len; | |
152 | mem_avoid[0].start = unsafe; | |
153 | mem_avoid[0].size = unsafe_len; | |
154 | ||
155 | /* Avoid initrd. */ | |
156 | initrd_start = (u64)real_mode->ext_ramdisk_image << 32; | |
157 | initrd_start |= real_mode->hdr.ramdisk_image; | |
158 | initrd_size = (u64)real_mode->ext_ramdisk_size << 32; | |
159 | initrd_size |= real_mode->hdr.ramdisk_size; | |
160 | mem_avoid[1].start = initrd_start; | |
161 | mem_avoid[1].size = initrd_size; | |
162 | ||
163 | /* Avoid kernel command line. */ | |
164 | cmd_line = (u64)real_mode->ext_cmd_line_ptr << 32; | |
165 | cmd_line |= real_mode->hdr.cmd_line_ptr; | |
166 | /* Calculate size of cmd_line. */ | |
167 | ptr = (char *)(unsigned long)cmd_line; | |
168 | for (cmd_line_size = 0; ptr[cmd_line_size++]; ) | |
169 | ; | |
170 | mem_avoid[2].start = cmd_line; | |
171 | mem_avoid[2].size = cmd_line_size; | |
172 | ||
173 | /* Avoid heap memory. */ | |
174 | mem_avoid[3].start = (unsigned long)free_mem_ptr; | |
175 | mem_avoid[3].size = BOOT_HEAP_SIZE; | |
176 | ||
177 | /* Avoid stack memory. */ | |
178 | mem_avoid[4].start = (unsigned long)free_mem_end_ptr; | |
179 | mem_avoid[4].size = BOOT_STACK_SIZE; | |
180 | } | |
181 | ||
182 | /* Does this memory vector overlap a known avoided area? */ | |
183 | bool mem_avoid_overlap(struct mem_vector *img) | |
184 | { | |
185 | int i; | |
186 | ||
187 | for (i = 0; i < MEM_AVOID_MAX; i++) { | |
188 | if (mem_overlaps(img, &mem_avoid[i])) | |
189 | return true; | |
190 | } | |
191 | ||
192 | return false; | |
193 | } | |
194 | ||
195 | unsigned long slots[CONFIG_RANDOMIZE_BASE_MAX_OFFSET / CONFIG_PHYSICAL_ALIGN]; | |
196 | unsigned long slot_max = 0; | |
197 | ||
198 | static void slots_append(unsigned long addr) | |
199 | { | |
200 | /* Overflowing the slots list should be impossible. */ | |
201 | if (slot_max >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET / | |
202 | CONFIG_PHYSICAL_ALIGN) | |
203 | return; | |
204 | ||
205 | slots[slot_max++] = addr; | |
206 | } | |
207 | ||
208 | static unsigned long slots_fetch_random(void) | |
209 | { | |
210 | /* Handle case of no slots stored. */ | |
211 | if (slot_max == 0) | |
212 | return 0; | |
213 | ||
214 | return slots[get_random_long() % slot_max]; | |
215 | } | |
216 | ||
217 | static void process_e820_entry(struct e820entry *entry, | |
218 | unsigned long minimum, | |
219 | unsigned long image_size) | |
220 | { | |
221 | struct mem_vector region, img; | |
222 | ||
223 | /* Skip non-RAM entries. */ | |
224 | if (entry->type != E820_RAM) | |
225 | return; | |
226 | ||
227 | /* Ignore entries entirely above our maximum. */ | |
228 | if (entry->addr >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET) | |
229 | return; | |
230 | ||
231 | /* Ignore entries entirely below our minimum. */ | |
232 | if (entry->addr + entry->size < minimum) | |
233 | return; | |
234 | ||
235 | region.start = entry->addr; | |
236 | region.size = entry->size; | |
237 | ||
238 | /* Potentially raise address to minimum location. */ | |
239 | if (region.start < minimum) | |
240 | region.start = minimum; | |
241 | ||
242 | /* Potentially raise address to meet alignment requirements. */ | |
243 | region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN); | |
244 | ||
245 | /* Did we raise the address above the bounds of this e820 region? */ | |
246 | if (region.start > entry->addr + entry->size) | |
247 | return; | |
248 | ||
249 | /* Reduce size by any delta from the original address. */ | |
250 | region.size -= region.start - entry->addr; | |
251 | ||
252 | /* Reduce maximum size to fit end of image within maximum limit. */ | |
253 | if (region.start + region.size > CONFIG_RANDOMIZE_BASE_MAX_OFFSET) | |
254 | region.size = CONFIG_RANDOMIZE_BASE_MAX_OFFSET - region.start; | |
255 | ||
256 | /* Walk each aligned slot and check for avoided areas. */ | |
257 | for (img.start = region.start, img.size = image_size ; | |
258 | mem_contains(®ion, &img) ; | |
259 | img.start += CONFIG_PHYSICAL_ALIGN) { | |
260 | if (mem_avoid_overlap(&img)) | |
261 | continue; | |
262 | slots_append(img.start); | |
263 | } | |
264 | } | |
265 | ||
266 | static unsigned long find_random_addr(unsigned long minimum, | |
267 | unsigned long size) | |
268 | { | |
269 | int i; | |
270 | unsigned long addr; | |
271 | ||
272 | /* Make sure minimum is aligned. */ | |
273 | minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN); | |
274 | ||
275 | /* Verify potential e820 positions, appending to slots list. */ | |
276 | for (i = 0; i < real_mode->e820_entries; i++) { | |
277 | process_e820_entry(&real_mode->e820_map[i], minimum, size); | |
278 | } | |
279 | ||
280 | return slots_fetch_random(); | |
281 | } | |
282 | ||
8ab3820f KC |
283 | unsigned char *choose_kernel_location(unsigned char *input, |
284 | unsigned long input_size, | |
285 | unsigned char *output, | |
286 | unsigned long output_size) | |
287 | { | |
288 | unsigned long choice = (unsigned long)output; | |
82fa9637 | 289 | unsigned long random; |
8ab3820f KC |
290 | |
291 | if (cmdline_find_option_bool("nokaslr")) { | |
292 | debug_putstr("KASLR disabled...\n"); | |
293 | goto out; | |
294 | } | |
295 | ||
82fa9637 KC |
296 | /* Record the various known unsafe memory ranges. */ |
297 | mem_avoid_init((unsigned long)input, input_size, | |
298 | (unsigned long)output, output_size); | |
299 | ||
300 | /* Walk e820 and find a random address. */ | |
301 | random = find_random_addr(choice, output_size); | |
302 | if (!random) { | |
303 | debug_putstr("KASLR could not find suitable E820 region...\n"); | |
304 | goto out; | |
305 | } | |
306 | ||
307 | /* Always enforce the minimum. */ | |
308 | if (random < choice) | |
309 | goto out; | |
8ab3820f | 310 | |
82fa9637 | 311 | choice = random; |
8ab3820f KC |
312 | out: |
313 | return (unsigned char *)choice; | |
314 | } | |
315 | ||
316 | #endif /* CONFIG_RANDOMIZE_BASE */ |