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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 KC |
7 | |
8 | #define I8254_PORT_CONTROL 0x43 | |
9 | #define I8254_PORT_COUNTER0 0x40 | |
10 | #define I8254_CMD_READBACK 0xC0 | |
11 | #define I8254_SELECT_COUNTER0 0x02 | |
12 | #define I8254_STATUS_NOTREADY 0x40 | |
13 | static inline u16 i8254(void) | |
14 | { | |
15 | u16 status, timer; | |
16 | ||
17 | do { | |
18 | outb(I8254_PORT_CONTROL, | |
19 | I8254_CMD_READBACK | I8254_SELECT_COUNTER0); | |
20 | status = inb(I8254_PORT_COUNTER0); | |
21 | timer = inb(I8254_PORT_COUNTER0); | |
22 | timer |= inb(I8254_PORT_COUNTER0) << 8; | |
23 | } while (status & I8254_STATUS_NOTREADY); | |
24 | ||
25 | return timer; | |
26 | } | |
27 | ||
28 | static unsigned long get_random_long(void) | |
29 | { | |
30 | unsigned long random; | |
31 | ||
32 | if (has_cpuflag(X86_FEATURE_RDRAND)) { | |
33 | debug_putstr("KASLR using RDRAND...\n"); | |
34 | if (rdrand_long(&random)) | |
35 | return random; | |
36 | } | |
37 | ||
38 | if (has_cpuflag(X86_FEATURE_TSC)) { | |
39 | uint32_t raw; | |
40 | ||
41 | debug_putstr("KASLR using RDTSC...\n"); | |
42 | rdtscl(raw); | |
43 | ||
44 | /* Only use the low bits of rdtsc. */ | |
45 | random = raw & 0xffff; | |
46 | } else { | |
47 | debug_putstr("KASLR using i8254...\n"); | |
48 | random = i8254(); | |
49 | } | |
50 | ||
51 | /* Extend timer bits poorly... */ | |
52 | random |= (random << 16); | |
53 | #ifdef CONFIG_X86_64 | |
54 | random |= (random << 32); | |
55 | #endif | |
56 | return random; | |
57 | } | |
8ab3820f | 58 | |
82fa9637 KC |
59 | struct mem_vector { |
60 | unsigned long start; | |
61 | unsigned long size; | |
62 | }; | |
63 | ||
64 | #define MEM_AVOID_MAX 5 | |
65 | struct mem_vector mem_avoid[MEM_AVOID_MAX]; | |
66 | ||
67 | static bool mem_contains(struct mem_vector *region, struct mem_vector *item) | |
68 | { | |
69 | /* Item at least partially before region. */ | |
70 | if (item->start < region->start) | |
71 | return false; | |
72 | /* Item at least partially after region. */ | |
73 | if (item->start + item->size > region->start + region->size) | |
74 | return false; | |
75 | return true; | |
76 | } | |
77 | ||
78 | static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two) | |
79 | { | |
80 | /* Item one is entirely before item two. */ | |
81 | if (one->start + one->size <= two->start) | |
82 | return false; | |
83 | /* Item one is entirely after item two. */ | |
84 | if (one->start >= two->start + two->size) | |
85 | return false; | |
86 | return true; | |
87 | } | |
88 | ||
89 | static void mem_avoid_init(unsigned long input, unsigned long input_size, | |
90 | unsigned long output, unsigned long output_size) | |
91 | { | |
92 | u64 initrd_start, initrd_size; | |
93 | u64 cmd_line, cmd_line_size; | |
94 | unsigned long unsafe, unsafe_len; | |
95 | char *ptr; | |
96 | ||
97 | /* | |
98 | * Avoid the region that is unsafe to overlap during | |
99 | * decompression (see calculations at top of misc.c). | |
100 | */ | |
101 | unsafe_len = (output_size >> 12) + 32768 + 18; | |
102 | unsafe = (unsigned long)input + input_size - unsafe_len; | |
103 | mem_avoid[0].start = unsafe; | |
104 | mem_avoid[0].size = unsafe_len; | |
105 | ||
106 | /* Avoid initrd. */ | |
107 | initrd_start = (u64)real_mode->ext_ramdisk_image << 32; | |
108 | initrd_start |= real_mode->hdr.ramdisk_image; | |
109 | initrd_size = (u64)real_mode->ext_ramdisk_size << 32; | |
110 | initrd_size |= real_mode->hdr.ramdisk_size; | |
111 | mem_avoid[1].start = initrd_start; | |
112 | mem_avoid[1].size = initrd_size; | |
113 | ||
114 | /* Avoid kernel command line. */ | |
115 | cmd_line = (u64)real_mode->ext_cmd_line_ptr << 32; | |
116 | cmd_line |= real_mode->hdr.cmd_line_ptr; | |
117 | /* Calculate size of cmd_line. */ | |
118 | ptr = (char *)(unsigned long)cmd_line; | |
119 | for (cmd_line_size = 0; ptr[cmd_line_size++]; ) | |
120 | ; | |
121 | mem_avoid[2].start = cmd_line; | |
122 | mem_avoid[2].size = cmd_line_size; | |
123 | ||
124 | /* Avoid heap memory. */ | |
125 | mem_avoid[3].start = (unsigned long)free_mem_ptr; | |
126 | mem_avoid[3].size = BOOT_HEAP_SIZE; | |
127 | ||
128 | /* Avoid stack memory. */ | |
129 | mem_avoid[4].start = (unsigned long)free_mem_end_ptr; | |
130 | mem_avoid[4].size = BOOT_STACK_SIZE; | |
131 | } | |
132 | ||
133 | /* Does this memory vector overlap a known avoided area? */ | |
134 | bool mem_avoid_overlap(struct mem_vector *img) | |
135 | { | |
136 | int i; | |
137 | ||
138 | for (i = 0; i < MEM_AVOID_MAX; i++) { | |
139 | if (mem_overlaps(img, &mem_avoid[i])) | |
140 | return true; | |
141 | } | |
142 | ||
143 | return false; | |
144 | } | |
145 | ||
146 | unsigned long slots[CONFIG_RANDOMIZE_BASE_MAX_OFFSET / CONFIG_PHYSICAL_ALIGN]; | |
147 | unsigned long slot_max = 0; | |
148 | ||
149 | static void slots_append(unsigned long addr) | |
150 | { | |
151 | /* Overflowing the slots list should be impossible. */ | |
152 | if (slot_max >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET / | |
153 | CONFIG_PHYSICAL_ALIGN) | |
154 | return; | |
155 | ||
156 | slots[slot_max++] = addr; | |
157 | } | |
158 | ||
159 | static unsigned long slots_fetch_random(void) | |
160 | { | |
161 | /* Handle case of no slots stored. */ | |
162 | if (slot_max == 0) | |
163 | return 0; | |
164 | ||
165 | return slots[get_random_long() % slot_max]; | |
166 | } | |
167 | ||
168 | static void process_e820_entry(struct e820entry *entry, | |
169 | unsigned long minimum, | |
170 | unsigned long image_size) | |
171 | { | |
172 | struct mem_vector region, img; | |
173 | ||
174 | /* Skip non-RAM entries. */ | |
175 | if (entry->type != E820_RAM) | |
176 | return; | |
177 | ||
178 | /* Ignore entries entirely above our maximum. */ | |
179 | if (entry->addr >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET) | |
180 | return; | |
181 | ||
182 | /* Ignore entries entirely below our minimum. */ | |
183 | if (entry->addr + entry->size < minimum) | |
184 | return; | |
185 | ||
186 | region.start = entry->addr; | |
187 | region.size = entry->size; | |
188 | ||
189 | /* Potentially raise address to minimum location. */ | |
190 | if (region.start < minimum) | |
191 | region.start = minimum; | |
192 | ||
193 | /* Potentially raise address to meet alignment requirements. */ | |
194 | region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN); | |
195 | ||
196 | /* Did we raise the address above the bounds of this e820 region? */ | |
197 | if (region.start > entry->addr + entry->size) | |
198 | return; | |
199 | ||
200 | /* Reduce size by any delta from the original address. */ | |
201 | region.size -= region.start - entry->addr; | |
202 | ||
203 | /* Reduce maximum size to fit end of image within maximum limit. */ | |
204 | if (region.start + region.size > CONFIG_RANDOMIZE_BASE_MAX_OFFSET) | |
205 | region.size = CONFIG_RANDOMIZE_BASE_MAX_OFFSET - region.start; | |
206 | ||
207 | /* Walk each aligned slot and check for avoided areas. */ | |
208 | for (img.start = region.start, img.size = image_size ; | |
209 | mem_contains(®ion, &img) ; | |
210 | img.start += CONFIG_PHYSICAL_ALIGN) { | |
211 | if (mem_avoid_overlap(&img)) | |
212 | continue; | |
213 | slots_append(img.start); | |
214 | } | |
215 | } | |
216 | ||
217 | static unsigned long find_random_addr(unsigned long minimum, | |
218 | unsigned long size) | |
219 | { | |
220 | int i; | |
221 | unsigned long addr; | |
222 | ||
223 | /* Make sure minimum is aligned. */ | |
224 | minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN); | |
225 | ||
226 | /* Verify potential e820 positions, appending to slots list. */ | |
227 | for (i = 0; i < real_mode->e820_entries; i++) { | |
228 | process_e820_entry(&real_mode->e820_map[i], minimum, size); | |
229 | } | |
230 | ||
231 | return slots_fetch_random(); | |
232 | } | |
233 | ||
8ab3820f KC |
234 | unsigned char *choose_kernel_location(unsigned char *input, |
235 | unsigned long input_size, | |
236 | unsigned char *output, | |
237 | unsigned long output_size) | |
238 | { | |
239 | unsigned long choice = (unsigned long)output; | |
82fa9637 | 240 | unsigned long random; |
8ab3820f KC |
241 | |
242 | if (cmdline_find_option_bool("nokaslr")) { | |
243 | debug_putstr("KASLR disabled...\n"); | |
244 | goto out; | |
245 | } | |
246 | ||
82fa9637 KC |
247 | /* Record the various known unsafe memory ranges. */ |
248 | mem_avoid_init((unsigned long)input, input_size, | |
249 | (unsigned long)output, output_size); | |
250 | ||
251 | /* Walk e820 and find a random address. */ | |
252 | random = find_random_addr(choice, output_size); | |
253 | if (!random) { | |
254 | debug_putstr("KASLR could not find suitable E820 region...\n"); | |
255 | goto out; | |
256 | } | |
257 | ||
258 | /* Always enforce the minimum. */ | |
259 | if (random < choice) | |
260 | goto out; | |
8ab3820f | 261 | |
82fa9637 | 262 | choice = random; |
8ab3820f KC |
263 | out: |
264 | return (unsigned char *)choice; | |
265 | } | |
266 | ||
267 | #endif /* CONFIG_RANDOMIZE_BASE */ |