mm/kmsan/core.c

   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
  32 bool kmsan_enabled __read_mostly;
  33
  34 /*
  35  * Per-CPU KMSAN context to be used in interrupts, where current->kmsan is
  36  * unavaliable.
  37  */
  38 DEFINE_PER_CPU(struct kmsan_ctx, kmsan_percpu_ctx);
  39
  40 void 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
  50 void 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
  62 void 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
  67 depot_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. */
  82 void 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
 212 depot_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
 257 void 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
 294 struct 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
 308 void 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
 392 bool 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
 433 report:
 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 }