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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * KMSAN runtime library.
4 *
5 * Copyright (C) 2017-2022 Google LLC
6 * Author: Alexander Potapenko <glider@google.com>
7 *
8 */
9
10#include <asm/page.h>
11#include <linux/compiler.h>
12#include <linux/export.h>
13#include <linux/highmem.h>
14#include <linux/interrupt.h>
15#include <linux/kernel.h>
16#include <linux/kmsan_types.h>
17#include <linux/memory.h>
18#include <linux/mm.h>
19#include <linux/mm_types.h>
20#include <linux/mmzone.h>
21#include <linux/percpu-defs.h>
22#include <linux/preempt.h>
23#include <linux/slab.h>
24#include <linux/stackdepot.h>
25#include <linux/stacktrace.h>
26#include <linux/types.h>
27#include <linux/vmalloc.h>
28
29#include "../slab.h"
30#include "kmsan.h"
31
32bool kmsan_enabled __read_mostly;
33
34/*
35 * Per-CPU KMSAN context to be used in interrupts, where current->kmsan is
36 * unavaliable.
37 */
38DEFINE_PER_CPU(struct kmsan_ctx, kmsan_percpu_ctx);
39
40void kmsan_internal_task_create(struct task_struct *task)
41{
42 struct kmsan_ctx *ctx = &task->kmsan_ctx;
43 struct thread_info *info = current_thread_info();
44
45 __memset(ctx, 0, sizeof(*ctx));
46 ctx->allow_reporting = true;
47 kmsan_internal_unpoison_memory(info, sizeof(*info), false);
48}
49
50void kmsan_internal_poison_memory(void *address, size_t size, gfp_t flags,
51 unsigned int poison_flags)
52{
53 u32 extra_bits =
54 kmsan_extra_bits(/*depth*/ 0, poison_flags & KMSAN_POISON_FREE);
55 bool checked = poison_flags & KMSAN_POISON_CHECK;
56 depot_stack_handle_t handle;
57
58 handle = kmsan_save_stack_with_flags(flags, extra_bits);
59 kmsan_internal_set_shadow_origin(address, size, -1, handle, checked);
60}
61
62void kmsan_internal_unpoison_memory(void *address, size_t size, bool checked)
63{
64 kmsan_internal_set_shadow_origin(address, size, 0, 0, checked);
65}
66
67depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags,
68 unsigned int extra)
69{
70 unsigned long entries[KMSAN_STACK_DEPTH];
71 unsigned int nr_entries;
72
73 nr_entries = stack_trace_save(entries, KMSAN_STACK_DEPTH, 0);
74
75 /* Don't sleep (see might_sleep_if() in __alloc_pages_nodemask()). */
76 flags &= ~__GFP_DIRECT_RECLAIM;
77
78 return __stack_depot_save(entries, nr_entries, extra, flags, true);
79}
80
81/* Copy the metadata following the memmove() behavior. */
82void kmsan_internal_memmove_metadata(void *dst, void *src, size_t n)
83{
84 depot_stack_handle_t old_origin = 0, new_origin = 0;
85 int src_slots, dst_slots, i, iter, step, skip_bits;
86 depot_stack_handle_t *origin_src, *origin_dst;
87 void *shadow_src, *shadow_dst;
88 u32 *align_shadow_src, shadow;
89 bool backwards;
90
91 shadow_dst = kmsan_get_metadata(dst, KMSAN_META_SHADOW);
92 if (!shadow_dst)
93 return;
94 KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(dst, n));
95
96 shadow_src = kmsan_get_metadata(src, KMSAN_META_SHADOW);
97 if (!shadow_src) {
98 /*
99 * @src is untracked: zero out destination shadow, ignore the
100 * origins, we're done.
101 */
102 __memset(shadow_dst, 0, n);
103 return;
104 }
105 KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(src, n));
106
107 __memmove(shadow_dst, shadow_src, n);
108
109 origin_dst = kmsan_get_metadata(dst, KMSAN_META_ORIGIN);
110 origin_src = kmsan_get_metadata(src, KMSAN_META_ORIGIN);
111 KMSAN_WARN_ON(!origin_dst || !origin_src);
112 src_slots = (ALIGN((u64)src + n, KMSAN_ORIGIN_SIZE) -
113 ALIGN_DOWN((u64)src, KMSAN_ORIGIN_SIZE)) /
114 KMSAN_ORIGIN_SIZE;
115 dst_slots = (ALIGN((u64)dst + n, KMSAN_ORIGIN_SIZE) -
116 ALIGN_DOWN((u64)dst, KMSAN_ORIGIN_SIZE)) /
117 KMSAN_ORIGIN_SIZE;
118 KMSAN_WARN_ON((src_slots < 1) || (dst_slots < 1));
119 KMSAN_WARN_ON((src_slots - dst_slots > 1) ||
120 (dst_slots - src_slots < -1));
121
122 backwards = dst > src;
123 i = backwards ? min(src_slots, dst_slots) - 1 : 0;
124 iter = backwards ? -1 : 1;
125
126 align_shadow_src =
127 (u32 *)ALIGN_DOWN((u64)shadow_src, KMSAN_ORIGIN_SIZE);
128 for (step = 0; step < min(src_slots, dst_slots); step++, i += iter) {
129 KMSAN_WARN_ON(i < 0);
130 shadow = align_shadow_src[i];
131 if (i == 0) {
132 /*
133 * If @src isn't aligned on KMSAN_ORIGIN_SIZE, don't
134 * look at the first @src % KMSAN_ORIGIN_SIZE bytes
135 * of the first shadow slot.
136 */
137 skip_bits = ((u64)src % KMSAN_ORIGIN_SIZE) * 8;
138 shadow = (shadow >> skip_bits) << skip_bits;
139 }
140 if (i == src_slots - 1) {
141 /*
142 * If @src + n isn't aligned on
143 * KMSAN_ORIGIN_SIZE, don't look at the last
144 * (@src + n) % KMSAN_ORIGIN_SIZE bytes of the
145 * last shadow slot.
146 */
147 skip_bits = (((u64)src + n) % KMSAN_ORIGIN_SIZE) * 8;
148 shadow = (shadow << skip_bits) >> skip_bits;
149 }
150 /*
151 * Overwrite the origin only if the corresponding
152 * shadow is nonempty.
153 */
154 if (origin_src[i] && (origin_src[i] != old_origin) && shadow) {
155 old_origin = origin_src[i];
156 new_origin = kmsan_internal_chain_origin(old_origin);
157 /*
158 * kmsan_internal_chain_origin() may return
159 * NULL, but we don't want to lose the previous
160 * origin value.
161 */
162 if (!new_origin)
163 new_origin = old_origin;
164 }
165 if (shadow)
166 origin_dst[i] = new_origin;
167 else
168 origin_dst[i] = 0;
169 }
170 /*
171 * If dst_slots is greater than src_slots (i.e.
172 * dst_slots == src_slots + 1), there is an extra origin slot at the
173 * beginning or end of the destination buffer, for which we take the
174 * origin from the previous slot.
175 * This is only done if the part of the source shadow corresponding to
176 * slot is non-zero.
177 *
178 * E.g. if we copy 8 aligned bytes that are marked as uninitialized
179 * and have origins o111 and o222, to an unaligned buffer with offset 1,
180 * these two origins are copied to three origin slots, so one of then
181 * needs to be duplicated, depending on the copy direction (@backwards)
182 *
183 * src shadow: |uuuu|uuuu|....|
184 * src origin: |o111|o222|....|
185 *
186 * backwards = 0:
187 * dst shadow: |.uuu|uuuu|u...|
188 * dst origin: |....|o111|o222| - fill the empty slot with o111
189 * backwards = 1:
190 * dst shadow: |.uuu|uuuu|u...|
191 * dst origin: |o111|o222|....| - fill the empty slot with o222
192 */
193 if (src_slots < dst_slots) {
194 if (backwards) {
195 shadow = align_shadow_src[src_slots - 1];
196 skip_bits = (((u64)dst + n) % KMSAN_ORIGIN_SIZE) * 8;
197 shadow = (shadow << skip_bits) >> skip_bits;
198 if (shadow)
199 /* src_slots > 0, therefore dst_slots is at least 2 */
200 origin_dst[dst_slots - 1] =
201 origin_dst[dst_slots - 2];
202 } else {
203 shadow = align_shadow_src[0];
204 skip_bits = ((u64)dst % KMSAN_ORIGIN_SIZE) * 8;
205 shadow = (shadow >> skip_bits) << skip_bits;
206 if (shadow)
207 origin_dst[0] = origin_dst[1];
208 }
209 }
210}
211
212depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id)
213{
214 unsigned long entries[3];
215 u32 extra_bits;
216 int depth;
217 bool uaf;
218
219 if (!id)
220 return id;
221 /*
222 * Make sure we have enough spare bits in @id to hold the UAF bit and
223 * the chain depth.
224 */
225 BUILD_BUG_ON(
226 (1 << STACK_DEPOT_EXTRA_BITS) <= (KMSAN_MAX_ORIGIN_DEPTH << 1));
227
228 extra_bits = stack_depot_get_extra_bits(id);
229 depth = kmsan_depth_from_eb(extra_bits);
230 uaf = kmsan_uaf_from_eb(extra_bits);
231
232 /*
233 * Stop chaining origins once the depth reached KMSAN_MAX_ORIGIN_DEPTH.
234 * This mostly happens in the case structures with uninitialized padding
235 * are copied around many times. Origin chains for such structures are
236 * usually periodic, and it does not make sense to fully store them.
237 */
238 if (depth == KMSAN_MAX_ORIGIN_DEPTH)
239 return id;
240
241 depth++;
242 extra_bits = kmsan_extra_bits(depth, uaf);
243
244 entries[0] = KMSAN_CHAIN_MAGIC_ORIGIN;
245 entries[1] = kmsan_save_stack_with_flags(GFP_ATOMIC, 0);
246 entries[2] = id;
247 /*
248 * @entries is a local var in non-instrumented code, so KMSAN does not
249 * know it is initialized. Explicitly unpoison it to avoid false
250 * positives when __stack_depot_save() passes it to instrumented code.
251 */
252 kmsan_internal_unpoison_memory(entries, sizeof(entries), false);
253 return __stack_depot_save(entries, ARRAY_SIZE(entries), extra_bits,
254 GFP_ATOMIC, true);
255}
256
257void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b,
258 u32 origin, bool checked)
259{
260 u64 address = (u64)addr;
261 void *shadow_start;
262 u32 *origin_start;
263 size_t pad = 0;
264
265 KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size));
266 shadow_start = kmsan_get_metadata(addr, KMSAN_META_SHADOW);
267 if (!shadow_start) {
268 /*
269 * kmsan_metadata_is_contiguous() is true, so either all shadow
270 * and origin pages are NULL, or all are non-NULL.
271 */
272 if (checked) {
273 pr_err("%s: not memsetting %ld bytes starting at %px, because the shadow is NULL\n",
274 __func__, size, addr);
275 KMSAN_WARN_ON(true);
276 }
277 return;
278 }
279 __memset(shadow_start, b, size);
280
281 if (!IS_ALIGNED(address, KMSAN_ORIGIN_SIZE)) {
282 pad = address % KMSAN_ORIGIN_SIZE;
283 address -= pad;
284 size += pad;
285 }
286 size = ALIGN(size, KMSAN_ORIGIN_SIZE);
287 origin_start =
288 (u32 *)kmsan_get_metadata((void *)address, KMSAN_META_ORIGIN);
289
290 for (int i = 0; i < size / KMSAN_ORIGIN_SIZE; i++)
291 origin_start[i] = origin;
292}
293
294struct page *kmsan_vmalloc_to_page_or_null(void *vaddr)
295{
296 struct page *page;
297
298 if (!kmsan_internal_is_vmalloc_addr(vaddr) &&
299 !kmsan_internal_is_module_addr(vaddr))
300 return NULL;
301 page = vmalloc_to_page(vaddr);
302 if (pfn_valid(page_to_pfn(page)))
303 return page;
304 else
305 return NULL;
306}
307
308void kmsan_internal_check_memory(void *addr, size_t size, const void *user_addr,
309 int reason)
310{
311 depot_stack_handle_t cur_origin = 0, new_origin = 0;
312 unsigned long addr64 = (unsigned long)addr;
313 depot_stack_handle_t *origin = NULL;
314 unsigned char *shadow = NULL;
315 int cur_off_start = -1;
316 int chunk_size;
317 size_t pos = 0;
318
319 if (!size)
320 return;
321 KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size));
322 while (pos < size) {
323 chunk_size = min(size - pos,
324 PAGE_SIZE - ((addr64 + pos) % PAGE_SIZE));
325 shadow = kmsan_get_metadata((void *)(addr64 + pos),
326 KMSAN_META_SHADOW);
327 if (!shadow) {
328 /*
329 * This page is untracked. If there were uninitialized
330 * bytes before, report them.
331 */
332 if (cur_origin) {
333 kmsan_enter_runtime();
334 kmsan_report(cur_origin, addr, size,
335 cur_off_start, pos - 1, user_addr,
336 reason);
337 kmsan_leave_runtime();
338 }
339 cur_origin = 0;
340 cur_off_start = -1;
341 pos += chunk_size;
342 continue;
343 }
344 for (int i = 0; i < chunk_size; i++) {
345 if (!shadow[i]) {
346 /*
347 * This byte is unpoisoned. If there were
348 * poisoned bytes before, report them.
349 */
350 if (cur_origin) {
351 kmsan_enter_runtime();
352 kmsan_report(cur_origin, addr, size,
353 cur_off_start, pos + i - 1,
354 user_addr, reason);
355 kmsan_leave_runtime();
356 }
357 cur_origin = 0;
358 cur_off_start = -1;
359 continue;
360 }
361 origin = kmsan_get_metadata((void *)(addr64 + pos + i),
362 KMSAN_META_ORIGIN);
363 KMSAN_WARN_ON(!origin);
364 new_origin = *origin;
365 /*
366 * Encountered new origin - report the previous
367 * uninitialized range.
368 */
369 if (cur_origin != new_origin) {
370 if (cur_origin) {
371 kmsan_enter_runtime();
372 kmsan_report(cur_origin, addr, size,
373 cur_off_start, pos + i - 1,
374 user_addr, reason);
375 kmsan_leave_runtime();
376 }
377 cur_origin = new_origin;
378 cur_off_start = pos + i;
379 }
380 }
381 pos += chunk_size;
382 }
383 KMSAN_WARN_ON(pos != size);
384 if (cur_origin) {
385 kmsan_enter_runtime();
386 kmsan_report(cur_origin, addr, size, cur_off_start, pos - 1,
387 user_addr, reason);
388 kmsan_leave_runtime();
389 }
390}
391
392bool kmsan_metadata_is_contiguous(void *addr, size_t size)
393{
394 char *cur_shadow = NULL, *next_shadow = NULL, *cur_origin = NULL,
395 *next_origin = NULL;
396 u64 cur_addr = (u64)addr, next_addr = cur_addr + PAGE_SIZE;
397 depot_stack_handle_t *origin_p;
398 bool all_untracked = false;
399
400 if (!size)
401 return true;
402
403 /* The whole range belongs to the same page. */
404 if (ALIGN_DOWN(cur_addr + size - 1, PAGE_SIZE) ==
405 ALIGN_DOWN(cur_addr, PAGE_SIZE))
406 return true;
407
408 cur_shadow = kmsan_get_metadata((void *)cur_addr, /*is_origin*/ false);
409 if (!cur_shadow)
410 all_untracked = true;
411 cur_origin = kmsan_get_metadata((void *)cur_addr, /*is_origin*/ true);
412 if (all_untracked && cur_origin)
413 goto report;
414
415 for (; next_addr < (u64)addr + size;
416 cur_addr = next_addr, cur_shadow = next_shadow,
417 cur_origin = next_origin, next_addr += PAGE_SIZE) {
418 next_shadow = kmsan_get_metadata((void *)next_addr, false);
419 next_origin = kmsan_get_metadata((void *)next_addr, true);
420 if (all_untracked) {
421 if (next_shadow || next_origin)
422 goto report;
423 if (!next_shadow && !next_origin)
424 continue;
425 }
426 if (((u64)cur_shadow == ((u64)next_shadow - PAGE_SIZE)) &&
427 ((u64)cur_origin == ((u64)next_origin - PAGE_SIZE)))
428 continue;
429 goto report;
430 }
431 return true;
432
433report:
434 pr_err("%s: attempting to access two shadow page ranges.\n", __func__);
435 pr_err("Access of size %ld at %px.\n", size, addr);
436 pr_err("Addresses belonging to different ranges: %px and %px\n",
437 (void *)cur_addr, (void *)next_addr);
438 pr_err("page[0].shadow: %px, page[1].shadow: %px\n", cur_shadow,
439 next_shadow);
440 pr_err("page[0].origin: %px, page[1].origin: %px\n", cur_origin,
441 next_origin);
442 origin_p = kmsan_get_metadata(addr, KMSAN_META_ORIGIN);
443 if (origin_p) {
444 pr_err("Origin: %08x\n", *origin_p);
445 kmsan_print_origin(*origin_p);
446 } else {
447 pr_err("Origin: unavailable\n");
448 }
449 return false;
450}