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         depot_stack_handle_t handle;
  73
  74         nr_entries = stack_trace_save(entries, KMSAN_STACK_DEPTH, 0);
  75
  76         /* Don't sleep. */
  77         flags &= ~(__GFP_DIRECT_RECLAIM | __GFP_KSWAPD_RECLAIM);
  78
  79         handle = stack_depot_save(entries, nr_entries, flags);
  80         return stack_depot_set_extra_bits(handle, extra);
  81 }
  82
  83 /* Copy the metadata following the memmove() behavior. */
  84 void kmsan_internal_memmove_metadata(void *dst, void *src, size_t n)
  85 {
  86         depot_stack_handle_t prev_old_origin = 0, prev_new_origin = 0;
  87         int i, iter, step, src_off, dst_off, oiter_src, oiter_dst;
  88         depot_stack_handle_t old_origin = 0, new_origin = 0;
  89         depot_stack_handle_t *origin_src, *origin_dst;
  90         u8 *shadow_src, *shadow_dst;
  91         u32 *align_shadow_dst;
  92         bool backwards;
  93
  94         shadow_dst = kmsan_get_metadata(dst, KMSAN_META_SHADOW);
  95         if (!shadow_dst)
  96                 return;
  97         KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(dst, n));
  98         align_shadow_dst =
  99                 (u32 *)ALIGN_DOWN((u64)shadow_dst, KMSAN_ORIGIN_SIZE);
 100
 101         shadow_src = kmsan_get_metadata(src, KMSAN_META_SHADOW);
 102         if (!shadow_src) {
 103                 /* @src is untracked: mark @dst as initialized. */
 104                 kmsan_internal_unpoison_memory(dst, n, /*checked*/ false);
 105                 return;
 106         }
 107         KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(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
 113         backwards = dst > src;
 114         step = backwards ? -1 : 1;
 115         iter = backwards ? n - 1 : 0;
 116         src_off = (u64)src % KMSAN_ORIGIN_SIZE;
 117         dst_off = (u64)dst % KMSAN_ORIGIN_SIZE;
 118
 119         /* Copy shadow bytes one by one, updating the origins if necessary. */
 120         for (i = 0; i < n; i++, iter += step) {
 121                 oiter_src = (iter + src_off) / KMSAN_ORIGIN_SIZE;
 122                 oiter_dst = (iter + dst_off) / KMSAN_ORIGIN_SIZE;
 123                 if (!shadow_src[iter]) {
 124                         shadow_dst[iter] = 0;
 125                         if (!align_shadow_dst[oiter_dst])
 126                                 origin_dst[oiter_dst] = 0;
 127                         continue;
 128                 }
 129                 shadow_dst[iter] = shadow_src[iter];
 130                 old_origin = origin_src[oiter_src];
 131                 if (old_origin == prev_old_origin)
 132                         new_origin = prev_new_origin;
 133                 else {
 134                         /*
 135                          * kmsan_internal_chain_origin() may return
 136                          * NULL, but we don't want to lose the previous
 137                          * origin value.
 138                          */
 139                         new_origin = kmsan_internal_chain_origin(old_origin);
 140                         if (!new_origin)
 141                                 new_origin = old_origin;
 142                 }
 143                 origin_dst[oiter_dst] = new_origin;
 144                 prev_new_origin = new_origin;
 145                 prev_old_origin = old_origin;
 146         }
 147 }
 148
 149 depot_stack_handle_t kmsan_internal_chain_origin(depot_stack_handle_t id)
 150 {
 151         unsigned long entries[3];
 152         u32 extra_bits;
 153         int depth;
 154         bool uaf;
 155         depot_stack_handle_t handle;
 156
 157         if (!id)
 158                 return id;
 159         /*
 160          * Make sure we have enough spare bits in @id to hold the UAF bit and
 161          * the chain depth.
 162          */
 163         BUILD_BUG_ON(
 164                 (1 << STACK_DEPOT_EXTRA_BITS) <= (KMSAN_MAX_ORIGIN_DEPTH << 1));
 165
 166         extra_bits = stack_depot_get_extra_bits(id);
 167         depth = kmsan_depth_from_eb(extra_bits);
 168         uaf = kmsan_uaf_from_eb(extra_bits);
 169
 170         /*
 171          * Stop chaining origins once the depth reached KMSAN_MAX_ORIGIN_DEPTH.
 172          * This mostly happens in the case structures with uninitialized padding
 173          * are copied around many times. Origin chains for such structures are
 174          * usually periodic, and it does not make sense to fully store them.
 175          */
 176         if (depth == KMSAN_MAX_ORIGIN_DEPTH)
 177                 return id;
 178
 179         depth++;
 180         extra_bits = kmsan_extra_bits(depth, uaf);
 181
 182         entries[0] = KMSAN_CHAIN_MAGIC_ORIGIN;
 183         entries[1] = kmsan_save_stack_with_flags(__GFP_HIGH, 0);
 184         entries[2] = id;
 185         /*
 186          * @entries is a local var in non-instrumented code, so KMSAN does not
 187          * know it is initialized. Explicitly unpoison it to avoid false
 188          * positives when stack_depot_save() passes it to instrumented code.
 189          */
 190         kmsan_internal_unpoison_memory(entries, sizeof(entries), false);
 191         handle = stack_depot_save(entries, ARRAY_SIZE(entries), __GFP_HIGH);
 192         return stack_depot_set_extra_bits(handle, extra_bits);
 193 }
 194
 195 void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b,
 196                                       u32 origin, bool checked)
 197 {
 198         u64 address = (u64)addr;
 199         void *shadow_start;
 200         u32 *origin_start;
 201         size_t pad = 0;
 202
 203         KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size));
 204         shadow_start = kmsan_get_metadata(addr, KMSAN_META_SHADOW);
 205         if (!shadow_start) {
 206                 /*
 207                  * kmsan_metadata_is_contiguous() is true, so either all shadow
 208                  * and origin pages are NULL, or all are non-NULL.
 209                  */
 210                 if (checked) {
 211                         pr_err("%s: not memsetting %ld bytes starting at %px, because the shadow is NULL\n",
 212                                __func__, size, addr);
 213                         KMSAN_WARN_ON(true);
 214                 }
 215                 return;
 216         }
 217         __memset(shadow_start, b, size);
 218
 219         if (!IS_ALIGNED(address, KMSAN_ORIGIN_SIZE)) {
 220                 pad = address % KMSAN_ORIGIN_SIZE;
 221                 address -= pad;
 222                 size += pad;
 223         }
 224         size = ALIGN(size, KMSAN_ORIGIN_SIZE);
 225         origin_start =
 226                 (u32 *)kmsan_get_metadata((void *)address, KMSAN_META_ORIGIN);
 227
 228         for (int i = 0; i < size / KMSAN_ORIGIN_SIZE; i++)
 229                 origin_start[i] = origin;
 230 }
 231
 232 struct page *kmsan_vmalloc_to_page_or_null(void *vaddr)
 233 {
 234         struct page *page;
 235
 236         if (!kmsan_internal_is_vmalloc_addr(vaddr) &&
 237             !kmsan_internal_is_module_addr(vaddr))
 238                 return NULL;
 239         page = vmalloc_to_page(vaddr);
 240         if (pfn_valid(page_to_pfn(page)))
 241                 return page;
 242         else
 243                 return NULL;
 244 }
 245
 246 void kmsan_internal_check_memory(void *addr, size_t size, const void *user_addr,
 247                                  int reason)
 248 {
 249         depot_stack_handle_t cur_origin = 0, new_origin = 0;
 250         unsigned long addr64 = (unsigned long)addr;
 251         depot_stack_handle_t *origin = NULL;
 252         unsigned char *shadow = NULL;
 253         int cur_off_start = -1;
 254         int chunk_size;
 255         size_t pos = 0;
 256
 257         if (!size)
 258                 return;
 259         KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size));
 260         while (pos < size) {
 261                 chunk_size = min(size - pos,
 262                                  PAGE_SIZE - ((addr64 + pos) % PAGE_SIZE));
 263                 shadow = kmsan_get_metadata((void *)(addr64 + pos),
 264                                             KMSAN_META_SHADOW);
 265                 if (!shadow) {
 266                         /*
 267                          * This page is untracked. If there were uninitialized
 268                          * bytes before, report them.
 269                          */
 270                         if (cur_origin) {
 271                                 kmsan_enter_runtime();
 272                                 kmsan_report(cur_origin, addr, size,
 273                                              cur_off_start, pos - 1, user_addr,
 274                                              reason);
 275                                 kmsan_leave_runtime();
 276                         }
 277                         cur_origin = 0;
 278                         cur_off_start = -1;
 279                         pos += chunk_size;
 280                         continue;
 281                 }
 282                 for (int i = 0; i < chunk_size; i++) {
 283                         if (!shadow[i]) {
 284                                 /*
 285                                  * This byte is unpoisoned. If there were
 286                                  * poisoned bytes before, report them.
 287                                  */
 288                                 if (cur_origin) {
 289                                         kmsan_enter_runtime();
 290                                         kmsan_report(cur_origin, addr, size,
 291                                                      cur_off_start, pos + i - 1,
 292                                                      user_addr, reason);
 293                                         kmsan_leave_runtime();
 294                                 }
 295                                 cur_origin = 0;
 296                                 cur_off_start = -1;
 297                                 continue;
 298                         }
 299                         origin = kmsan_get_metadata((void *)(addr64 + pos + i),
 300                                                     KMSAN_META_ORIGIN);
 301                         KMSAN_WARN_ON(!origin);
 302                         new_origin = *origin;
 303                         /*
 304                          * Encountered new origin - report the previous
 305                          * uninitialized range.
 306                          */
 307                         if (cur_origin != new_origin) {
 308                                 if (cur_origin) {
 309                                         kmsan_enter_runtime();
 310                                         kmsan_report(cur_origin, addr, size,
 311                                                      cur_off_start, pos + i - 1,
 312                                                      user_addr, reason);
 313                                         kmsan_leave_runtime();
 314                                 }
 315                                 cur_origin = new_origin;
 316                                 cur_off_start = pos + i;
 317                         }
 318                 }
 319                 pos += chunk_size;
 320         }
 321         KMSAN_WARN_ON(pos != size);
 322         if (cur_origin) {
 323                 kmsan_enter_runtime();
 324                 kmsan_report(cur_origin, addr, size, cur_off_start, pos - 1,
 325                              user_addr, reason);
 326                 kmsan_leave_runtime();
 327         }
 328 }
 329
 330 bool kmsan_metadata_is_contiguous(void *addr, size_t size)
 331 {
 332         char *cur_shadow = NULL, *next_shadow = NULL, *cur_origin = NULL,
 333              *next_origin = NULL;
 334         u64 cur_addr = (u64)addr, next_addr = cur_addr + PAGE_SIZE;
 335         depot_stack_handle_t *origin_p;
 336         bool all_untracked = false;
 337
 338         if (!size)
 339                 return true;
 340
 341         /* The whole range belongs to the same page. */
 342         if (ALIGN_DOWN(cur_addr + size - 1, PAGE_SIZE) ==
 343             ALIGN_DOWN(cur_addr, PAGE_SIZE))
 344                 return true;
 345
 346         cur_shadow = kmsan_get_metadata((void *)cur_addr, /*is_origin*/ false);
 347         if (!cur_shadow)
 348                 all_untracked = true;
 349         cur_origin = kmsan_get_metadata((void *)cur_addr, /*is_origin*/ true);
 350         if (all_untracked && cur_origin)
 351                 goto report;
 352
 353         for (; next_addr < (u64)addr + size;
 354              cur_addr = next_addr, cur_shadow = next_shadow,
 355              cur_origin = next_origin, next_addr += PAGE_SIZE) {
 356                 next_shadow = kmsan_get_metadata((void *)next_addr, false);
 357                 next_origin = kmsan_get_metadata((void *)next_addr, true);
 358                 if (all_untracked) {
 359                         if (next_shadow || next_origin)
 360                                 goto report;
 361                         if (!next_shadow && !next_origin)
 362                                 continue;
 363                 }
 364                 if (((u64)cur_shadow == ((u64)next_shadow - PAGE_SIZE)) &&
 365                     ((u64)cur_origin == ((u64)next_origin - PAGE_SIZE)))
 366                         continue;
 367                 goto report;
 368         }
 369         return true;
 370
 371 report:
 372         pr_err("%s: attempting to access two shadow page ranges.\n", __func__);
 373         pr_err("Access of size %ld at %px.\n", size, addr);
 374         pr_err("Addresses belonging to different ranges: %px and %px\n",
 375                (void *)cur_addr, (void *)next_addr);
 376         pr_err("page[0].shadow: %px, page[1].shadow: %px\n", cur_shadow,
 377                next_shadow);
 378         pr_err("page[0].origin: %px, page[1].origin: %px\n", cur_origin,
 379                next_origin);
 380         origin_p = kmsan_get_metadata(addr, KMSAN_META_ORIGIN);
 381         if (origin_p) {
 382                 pr_err("Origin: %08x\n", *origin_p);
 383                 kmsan_print_origin(*origin_p);
 384         } else {
 385                 pr_err("Origin: unavailable\n");
 386         }
 387         return false;
 388 }