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1#include "misc.h"
2
3#ifdef CONFIG_RANDOMIZE_BASE
4#include <asm/msr.h>
5#include <asm/archrandom.h>
6#include <asm/e820.h>
7
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>
13
14/* Simplified build-specific string for starting entropy. */
15static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
16 LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
17
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
23static 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
38static 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. */
54static 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
64static unsigned long get_random_long(void)
65{
66#ifdef CONFIG_X86_64
67 const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
68#else
69 const unsigned long mix_const = 0x3f39e593UL;
70#endif
71 unsigned long raw, random = get_random_boot();
72 bool use_i8254 = true;
73
74 debug_putstr("KASLR using");
75
76 if (has_cpuflag(X86_FEATURE_RDRAND)) {
77 debug_putstr(" RDRAND");
78 if (rdrand_long(&raw)) {
79 random ^= raw;
80 use_i8254 = false;
81 }
82 }
83
84 if (has_cpuflag(X86_FEATURE_TSC)) {
85 debug_putstr(" RDTSC");
86 rdtscll(raw);
87
88 random ^= raw;
89 use_i8254 = false;
90 }
91
92 if (use_i8254) {
93 debug_putstr(" i8254");
94 random ^= i8254();
95 }
96
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
103 debug_putstr("...\n");
104
105 return random;
106}
107
108struct mem_vector {
109 unsigned long start;
110 unsigned long size;
111};
112
113#define MEM_AVOID_MAX 5
114static struct mem_vector mem_avoid[MEM_AVOID_MAX];
115
116static 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
127static 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
138static 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? */
183static 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
195static unsigned long slots[CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
196 CONFIG_PHYSICAL_ALIGN];
197static unsigned long slot_max;
198
199static void slots_append(unsigned long addr)
200{
201 /* Overflowing the slots list should be impossible. */
202 if (slot_max >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
203 CONFIG_PHYSICAL_ALIGN)
204 return;
205
206 slots[slot_max++] = addr;
207}
208
209static unsigned long slots_fetch_random(void)
210{
211 /* Handle case of no slots stored. */
212 if (slot_max == 0)
213 return 0;
214
215 return slots[get_random_long() % slot_max];
216}
217
218static void process_e820_entry(struct e820entry *entry,
219 unsigned long minimum,
220 unsigned long image_size)
221{
222 struct mem_vector region, img;
223
224 /* Skip non-RAM entries. */
225 if (entry->type != E820_RAM)
226 return;
227
228 /* Ignore entries entirely above our maximum. */
229 if (entry->addr >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET)
230 return;
231
232 /* Ignore entries entirely below our minimum. */
233 if (entry->addr + entry->size < minimum)
234 return;
235
236 region.start = entry->addr;
237 region.size = entry->size;
238
239 /* Potentially raise address to minimum location. */
240 if (region.start < minimum)
241 region.start = minimum;
242
243 /* Potentially raise address to meet alignment requirements. */
244 region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
245
246 /* Did we raise the address above the bounds of this e820 region? */
247 if (region.start > entry->addr + entry->size)
248 return;
249
250 /* Reduce size by any delta from the original address. */
251 region.size -= region.start - entry->addr;
252
253 /* Reduce maximum size to fit end of image within maximum limit. */
254 if (region.start + region.size > CONFIG_RANDOMIZE_BASE_MAX_OFFSET)
255 region.size = CONFIG_RANDOMIZE_BASE_MAX_OFFSET - region.start;
256
257 /* Walk each aligned slot and check for avoided areas. */
258 for (img.start = region.start, img.size = image_size ;
259 mem_contains(®ion, &img) ;
260 img.start += CONFIG_PHYSICAL_ALIGN) {
261 if (mem_avoid_overlap(&img))
262 continue;
263 slots_append(img.start);
264 }
265}
266
267static unsigned long find_random_addr(unsigned long minimum,
268 unsigned long size)
269{
270 int i;
271 unsigned long addr;
272
273 /* Make sure minimum is aligned. */
274 minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
275
276 /* Verify potential e820 positions, appending to slots list. */
277 for (i = 0; i < real_mode->e820_entries; i++) {
278 process_e820_entry(&real_mode->e820_map[i], minimum, size);
279 }
280
281 return slots_fetch_random();
282}
283
284unsigned char *choose_kernel_location(unsigned char *input,
285 unsigned long input_size,
286 unsigned char *output,
287 unsigned long output_size)
288{
289 unsigned long choice = (unsigned long)output;
290 unsigned long random;
291
292 if (cmdline_find_option_bool("nokaslr")) {
293 debug_putstr("KASLR disabled...\n");
294 goto out;
295 }
296
297 /* Record the various known unsafe memory ranges. */
298 mem_avoid_init((unsigned long)input, input_size,
299 (unsigned long)output, output_size);
300
301 /* Walk e820 and find a random address. */
302 random = find_random_addr(choice, output_size);
303 if (!random) {
304 debug_putstr("KASLR could not find suitable E820 region...\n");
305 goto out;
306 }
307
308 /* Always enforce the minimum. */
309 if (random < choice)
310 goto out;
311
312 choice = random;
313out:
314 return (unsigned char *)choice;
315}
316
317#endif /* CONFIG_RANDOMIZE_BASE */