3 #ifdef CONFIG_RANDOMIZE_BASE
5 #include <asm/archrandom.h>
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>
14 /* Simplified build-specific string for starting entropy. */
15 static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
16 LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
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)
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);
38 static unsigned long rotate_xor(unsigned long hash, const void *area,
42 unsigned long *ptr = (unsigned long *)area;
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);
53 /* Attempt to create a simple but unpredictable starting entropy. */
54 static unsigned long get_random_boot(void)
56 unsigned long hash = 0;
58 hash = rotate_xor(hash, build_str, sizeof(build_str));
59 hash = rotate_xor(hash, real_mode, sizeof(*real_mode));
64 static unsigned long get_random_long(void)
67 const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
69 const unsigned long mix_const = 0x3f39e593UL;
71 unsigned long raw, random = get_random_boot();
72 bool use_i8254 = true;
74 debug_putstr("KASLR using");
76 if (has_cpuflag(X86_FEATURE_RDRAND)) {
77 debug_putstr(" RDRAND");
78 if (rdrand_long(&raw)) {
84 if (has_cpuflag(X86_FEATURE_TSC)) {
85 debug_putstr(" RDTSC");
93 debug_putstr(" i8254");
97 /* Circular multiply for better bit diffusion */
99 : "=a" (random), "=d" (raw)
100 : "a" (random), "rm" (mix_const));
103 debug_putstr("...\n");
113 #define MEM_AVOID_MAX 5
114 struct mem_vector mem_avoid[MEM_AVOID_MAX];
116 static bool mem_contains(struct mem_vector *region, struct mem_vector *item)
118 /* Item at least partially before region. */
119 if (item->start < region->start)
121 /* Item at least partially after region. */
122 if (item->start + item->size > region->start + region->size)
127 static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
129 /* Item one is entirely before item two. */
130 if (one->start + one->size <= two->start)
132 /* Item one is entirely after item two. */
133 if (one->start >= two->start + two->size)
138 static void mem_avoid_init(unsigned long input, unsigned long input_size,
139 unsigned long output, unsigned long output_size)
141 u64 initrd_start, initrd_size;
142 u64 cmd_line, cmd_line_size;
143 unsigned long unsafe, unsafe_len;
147 * Avoid the region that is unsafe to overlap during
148 * decompression (see calculations at top of misc.c).
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;
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;
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++]; )
170 mem_avoid[2].start = cmd_line;
171 mem_avoid[2].size = cmd_line_size;
173 /* Avoid heap memory. */
174 mem_avoid[3].start = (unsigned long)free_mem_ptr;
175 mem_avoid[3].size = BOOT_HEAP_SIZE;
177 /* Avoid stack memory. */
178 mem_avoid[4].start = (unsigned long)free_mem_end_ptr;
179 mem_avoid[4].size = BOOT_STACK_SIZE;
182 /* Does this memory vector overlap a known avoided area? */
183 bool mem_avoid_overlap(struct mem_vector *img)
187 for (i = 0; i < MEM_AVOID_MAX; i++) {
188 if (mem_overlaps(img, &mem_avoid[i]))
195 unsigned long slots[CONFIG_RANDOMIZE_BASE_MAX_OFFSET / CONFIG_PHYSICAL_ALIGN];
196 unsigned long slot_max = 0;
198 static void slots_append(unsigned long addr)
200 /* Overflowing the slots list should be impossible. */
201 if (slot_max >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
202 CONFIG_PHYSICAL_ALIGN)
205 slots[slot_max++] = addr;
208 static unsigned long slots_fetch_random(void)
210 /* Handle case of no slots stored. */
214 return slots[get_random_long() % slot_max];
217 static void process_e820_entry(struct e820entry *entry,
218 unsigned long minimum,
219 unsigned long image_size)
221 struct mem_vector region, img;
223 /* Skip non-RAM entries. */
224 if (entry->type != E820_RAM)
227 /* Ignore entries entirely above our maximum. */
228 if (entry->addr >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET)
231 /* Ignore entries entirely below our minimum. */
232 if (entry->addr + entry->size < minimum)
235 region.start = entry->addr;
236 region.size = entry->size;
238 /* Potentially raise address to minimum location. */
239 if (region.start < minimum)
240 region.start = minimum;
242 /* Potentially raise address to meet alignment requirements. */
243 region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
245 /* Did we raise the address above the bounds of this e820 region? */
246 if (region.start > entry->addr + entry->size)
249 /* Reduce size by any delta from the original address. */
250 region.size -= region.start - entry->addr;
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;
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))
262 slots_append(img.start);
266 static unsigned long find_random_addr(unsigned long minimum,
272 /* Make sure minimum is aligned. */
273 minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
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);
280 return slots_fetch_random();
283 unsigned char *choose_kernel_location(unsigned char *input,
284 unsigned long input_size,
285 unsigned char *output,
286 unsigned long output_size)
288 unsigned long choice = (unsigned long)output;
289 unsigned long random;
291 if (cmdline_find_option_bool("nokaslr")) {
292 debug_putstr("KASLR disabled...\n");
296 /* Record the various known unsafe memory ranges. */
297 mem_avoid_init((unsigned long)input, input_size,
298 (unsigned long)output, output_size);
300 /* Walk e820 and find a random address. */
301 random = find_random_addr(choice, output_size);
303 debug_putstr("KASLR could not find suitable E820 region...\n");
307 /* Always enforce the minimum. */
313 return (unsigned char *)choice;
316 #endif /* CONFIG_RANDOMIZE_BASE */