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. */
14static 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
22static 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
37static 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. */
53static 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
63static 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		raw = rdtsc();
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
107struct mem_vector {
108	unsigned long start;
109	unsigned long size;
110};
111
112#define MEM_AVOID_MAX 5
113static struct mem_vector mem_avoid[MEM_AVOID_MAX];
114
115static 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
126static 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
137static 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? */
182static 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
209static unsigned long slots[CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
210			   CONFIG_PHYSICAL_ALIGN];
211static unsigned long slot_max;
212
213static 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
223static 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
232static 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
281static 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
298unsigned char *choose_kernel_location(struct boot_params *boot_params,
299				      unsigned char *input,
300				      unsigned long input_size,
301				      unsigned char *output,
302				      unsigned long output_size)
303{
304	unsigned long choice = (unsigned long)output;
305	unsigned long random;
306
307#ifdef CONFIG_HIBERNATION
308	if (!cmdline_find_option_bool("kaslr")) {
309		debug_putstr("KASLR disabled by default...\n");
310		goto out;
311	}
312#else
313	if (cmdline_find_option_bool("nokaslr")) {
314		debug_putstr("KASLR disabled by cmdline...\n");
315		goto out;
316	}
317#endif
318
319	boot_params->hdr.loadflags |= KASLR_FLAG;
320
321	/* Record the various known unsafe memory ranges. */
322	mem_avoid_init((unsigned long)input, input_size,
323		       (unsigned long)output, output_size);
324
325	/* Walk e820 and find a random address. */
326	random = find_random_addr(choice, output_size);
327	if (!random) {
328		debug_putstr("KASLR could not find suitable E820 region...\n");
329		goto out;
330	}
331
332	/* Always enforce the minimum. */
333	if (random < choice)
334		goto out;
335
336	choice = random;
337out:
338	return (unsigned char *)choice;
339}
340