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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(&region, &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