1 #include "misc.h"
2
3 #include <asm/msr.h>
4 #include <asm/archrandom.h>
5 #include <asm/e820.h>
6
7 #include <generated/compile.h>
8 #include <linux/module.h>
9 #include <linux/uts.h>
10 #include <linux/utsname.h>
11 #include <generated/utsrelease.h>
12
13 /* Simplified build-specific string for starting entropy. */
14 static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
15 LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
16
17 #define I8254_PORT_CONTROL 0x43
18 #define I8254_PORT_COUNTER0 0x40
19 #define I8254_CMD_READBACK 0xC0
20 #define I8254_SELECT_COUNTER0 0x02
21 #define I8254_STATUS_NOTREADY 0x40
i8254(void)22 static inline u16 i8254(void)
23 {
24 u16 status, timer;
25
26 do {
27 outb(I8254_PORT_CONTROL,
28 I8254_CMD_READBACK | I8254_SELECT_COUNTER0);
29 status = inb(I8254_PORT_COUNTER0);
30 timer = inb(I8254_PORT_COUNTER0);
31 timer |= inb(I8254_PORT_COUNTER0) << 8;
32 } while (status & I8254_STATUS_NOTREADY);
33
34 return timer;
35 }
36
rotate_xor(unsigned long hash,const void * area,size_t size)37 static unsigned long rotate_xor(unsigned long hash, const void *area,
38 size_t size)
39 {
40 size_t i;
41 unsigned long *ptr = (unsigned long *)area;
42
43 for (i = 0; i < size / sizeof(hash); i++) {
44 /* Rotate by odd number of bits and XOR. */
45 hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
46 hash ^= ptr[i];
47 }
48
49 return hash;
50 }
51
52 /* Attempt to create a simple but unpredictable starting entropy. */
get_random_boot(void)53 static unsigned long get_random_boot(void)
54 {
55 unsigned long hash = 0;
56
57 hash = rotate_xor(hash, build_str, sizeof(build_str));
58 hash = rotate_xor(hash, real_mode, sizeof(*real_mode));
59
60 return hash;
61 }
62
get_random_long(void)63 static unsigned long get_random_long(void)
64 {
65 #ifdef CONFIG_X86_64
66 const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
67 #else
68 const unsigned long mix_const = 0x3f39e593UL;
69 #endif
70 unsigned long raw, random = get_random_boot();
71 bool use_i8254 = true;
72
73 debug_putstr("KASLR using");
74
75 if (has_cpuflag(X86_FEATURE_RDRAND)) {
76 debug_putstr(" RDRAND");
77 if (rdrand_long(&raw)) {
78 random ^= raw;
79 use_i8254 = false;
80 }
81 }
82
83 if (has_cpuflag(X86_FEATURE_TSC)) {
84 debug_putstr(" RDTSC");
85 rdtscll(raw);
86
87 random ^= raw;
88 use_i8254 = false;
89 }
90
91 if (use_i8254) {
92 debug_putstr(" i8254");
93 random ^= i8254();
94 }
95
96 /* Circular multiply for better bit diffusion */
97 asm("mul %3"
98 : "=a" (random), "=d" (raw)
99 : "a" (random), "rm" (mix_const));
100 random += raw;
101
102 debug_putstr("...\n");
103
104 return random;
105 }
106
107 struct mem_vector {
108 unsigned long start;
109 unsigned long size;
110 };
111
112 #define MEM_AVOID_MAX 5
113 static struct mem_vector mem_avoid[MEM_AVOID_MAX];
114
mem_contains(struct mem_vector * region,struct mem_vector * item)115 static bool mem_contains(struct mem_vector *region, struct mem_vector *item)
116 {
117 /* Item at least partially before region. */
118 if (item->start < region->start)
119 return false;
120 /* Item at least partially after region. */
121 if (item->start + item->size > region->start + region->size)
122 return false;
123 return true;
124 }
125
mem_overlaps(struct mem_vector * one,struct mem_vector * two)126 static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
127 {
128 /* Item one is entirely before item two. */
129 if (one->start + one->size <= two->start)
130 return false;
131 /* Item one is entirely after item two. */
132 if (one->start >= two->start + two->size)
133 return false;
134 return true;
135 }
136
mem_avoid_init(unsigned long input,unsigned long input_size,unsigned long output,unsigned long output_size)137 static void mem_avoid_init(unsigned long input, unsigned long input_size,
138 unsigned long output, unsigned long output_size)
139 {
140 u64 initrd_start, initrd_size;
141 u64 cmd_line, cmd_line_size;
142 unsigned long unsafe, unsafe_len;
143 char *ptr;
144
145 /*
146 * Avoid the region that is unsafe to overlap during
147 * decompression (see calculations at top of misc.c).
148 */
149 unsafe_len = (output_size >> 12) + 32768 + 18;
150 unsafe = (unsigned long)input + input_size - unsafe_len;
151 mem_avoid[0].start = unsafe;
152 mem_avoid[0].size = unsafe_len;
153
154 /* Avoid initrd. */
155 initrd_start = (u64)real_mode->ext_ramdisk_image << 32;
156 initrd_start |= real_mode->hdr.ramdisk_image;
157 initrd_size = (u64)real_mode->ext_ramdisk_size << 32;
158 initrd_size |= real_mode->hdr.ramdisk_size;
159 mem_avoid[1].start = initrd_start;
160 mem_avoid[1].size = initrd_size;
161
162 /* Avoid kernel command line. */
163 cmd_line = (u64)real_mode->ext_cmd_line_ptr << 32;
164 cmd_line |= real_mode->hdr.cmd_line_ptr;
165 /* Calculate size of cmd_line. */
166 ptr = (char *)(unsigned long)cmd_line;
167 for (cmd_line_size = 0; ptr[cmd_line_size++]; )
168 ;
169 mem_avoid[2].start = cmd_line;
170 mem_avoid[2].size = cmd_line_size;
171
172 /* Avoid heap memory. */
173 mem_avoid[3].start = (unsigned long)free_mem_ptr;
174 mem_avoid[3].size = BOOT_HEAP_SIZE;
175
176 /* Avoid stack memory. */
177 mem_avoid[4].start = (unsigned long)free_mem_end_ptr;
178 mem_avoid[4].size = BOOT_STACK_SIZE;
179 }
180
181 /* Does this memory vector overlap a known avoided area? */
mem_avoid_overlap(struct mem_vector * img)182 static bool mem_avoid_overlap(struct mem_vector *img)
183 {
184 int i;
185 struct setup_data *ptr;
186
187 for (i = 0; i < MEM_AVOID_MAX; i++) {
188 if (mem_overlaps(img, &mem_avoid[i]))
189 return true;
190 }
191
192 /* Avoid all entries in the setup_data linked list. */
193 ptr = (struct setup_data *)(unsigned long)real_mode->hdr.setup_data;
194 while (ptr) {
195 struct mem_vector avoid;
196
197 avoid.start = (unsigned long)ptr;
198 avoid.size = sizeof(*ptr) + ptr->len;
199
200 if (mem_overlaps(img, &avoid))
201 return true;
202
203 ptr = (struct setup_data *)(unsigned long)ptr->next;
204 }
205
206 return false;
207 }
208
209 static unsigned long slots[CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
210 CONFIG_PHYSICAL_ALIGN];
211 static unsigned long slot_max;
212
slots_append(unsigned long addr)213 static void slots_append(unsigned long addr)
214 {
215 /* Overflowing the slots list should be impossible. */
216 if (slot_max >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
217 CONFIG_PHYSICAL_ALIGN)
218 return;
219
220 slots[slot_max++] = addr;
221 }
222
slots_fetch_random(void)223 static unsigned long slots_fetch_random(void)
224 {
225 /* Handle case of no slots stored. */
226 if (slot_max == 0)
227 return 0;
228
229 return slots[get_random_long() % slot_max];
230 }
231
process_e820_entry(struct e820entry * entry,unsigned long minimum,unsigned long image_size)232 static void process_e820_entry(struct e820entry *entry,
233 unsigned long minimum,
234 unsigned long image_size)
235 {
236 struct mem_vector region, img;
237
238 /* Skip non-RAM entries. */
239 if (entry->type != E820_RAM)
240 return;
241
242 /* Ignore entries entirely above our maximum. */
243 if (entry->addr >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET)
244 return;
245
246 /* Ignore entries entirely below our minimum. */
247 if (entry->addr + entry->size < minimum)
248 return;
249
250 region.start = entry->addr;
251 region.size = entry->size;
252
253 /* Potentially raise address to minimum location. */
254 if (region.start < minimum)
255 region.start = minimum;
256
257 /* Potentially raise address to meet alignment requirements. */
258 region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
259
260 /* Did we raise the address above the bounds of this e820 region? */
261 if (region.start > entry->addr + entry->size)
262 return;
263
264 /* Reduce size by any delta from the original address. */
265 region.size -= region.start - entry->addr;
266
267 /* Reduce maximum size to fit end of image within maximum limit. */
268 if (region.start + region.size > CONFIG_RANDOMIZE_BASE_MAX_OFFSET)
269 region.size = CONFIG_RANDOMIZE_BASE_MAX_OFFSET - region.start;
270
271 /* Walk each aligned slot and check for avoided areas. */
272 for (img.start = region.start, img.size = image_size ;
273 mem_contains(®ion, &img) ;
274 img.start += CONFIG_PHYSICAL_ALIGN) {
275 if (mem_avoid_overlap(&img))
276 continue;
277 slots_append(img.start);
278 }
279 }
280
find_random_addr(unsigned long minimum,unsigned long size)281 static unsigned long find_random_addr(unsigned long minimum,
282 unsigned long size)
283 {
284 int i;
285 unsigned long addr;
286
287 /* Make sure minimum is aligned. */
288 minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
289
290 /* Verify potential e820 positions, appending to slots list. */
291 for (i = 0; i < real_mode->e820_entries; i++) {
292 process_e820_entry(&real_mode->e820_map[i], minimum, size);
293 }
294
295 return slots_fetch_random();
296 }
297
choose_kernel_location(unsigned char * input,unsigned long input_size,unsigned char * output,unsigned long output_size)298 unsigned char *choose_kernel_location(unsigned char *input,
299 unsigned long input_size,
300 unsigned char *output,
301 unsigned long output_size)
302 {
303 unsigned long choice = (unsigned long)output;
304 unsigned long random;
305
306 #ifdef CONFIG_HIBERNATION
307 if (!cmdline_find_option_bool("kaslr")) {
308 debug_putstr("KASLR disabled by default...\n");
309 goto out;
310 }
311 #else
312 if (cmdline_find_option_bool("nokaslr")) {
313 debug_putstr("KASLR disabled by cmdline...\n");
314 goto out;
315 }
316 #endif
317
318 /* Record the various known unsafe memory ranges. */
319 mem_avoid_init((unsigned long)input, input_size,
320 (unsigned long)output, output_size);
321
322 /* Walk e820 and find a random address. */
323 random = find_random_addr(choice, output_size);
324 if (!random) {
325 debug_putstr("KASLR could not find suitable E820 region...\n");
326 goto out;
327 }
328
329 /* Always enforce the minimum. */
330 if (random < choice)
331 goto out;
332
333 choice = random;
334 out:
335 return (unsigned char *)choice;
336 }
337