mm/kfence/report.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * KFENCE reporting.
   4  *
   5  * Copyright (C) 2020, Google LLC.
   6  */
   7
   8 #include <stdarg.h>
   9
  10 #include <linux/kernel.h>
  11 #include <linux/lockdep.h>
  12 #include <linux/printk.h>
  13 #include <linux/sched/debug.h>
  14 #include <linux/seq_file.h>
  15 #include <linux/stacktrace.h>
  16 #include <linux/string.h>
  17 #include <trace/events/error_report.h>
  18
  19 #include <asm/kfence.h>
  20
  21 #include "kfence.h"
  22
  23 /* May be overridden by <asm/kfence.h>. */
  24 #ifndef ARCH_FUNC_PREFIX
  25 #define ARCH_FUNC_PREFIX ""
  26 #endif
  27
  28 extern bool no_hash_pointers;
  29
  30 /* Helper function to either print to a seq_file or to console. */
  31 __printf(2, 3)
  32 static void seq_con_printf(struct seq_file *seq, const char *fmt, ...)
  33 {
  34         va_list args;
  35
  36         va_start(args, fmt);
  37         if (seq)
  38                 seq_vprintf(seq, fmt, args);
  39         else
  40                 vprintk(fmt, args);
  41         va_end(args);
  42 }
  43
  44 /*
  45  * Get the number of stack entries to skip to get out of MM internals. @type is
  46  * optional, and if set to NULL, assumes an allocation or free stack.
  47  */
  48 static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries,
  49                             const enum kfence_error_type *type)
  50 {
  51         char buf[64];
  52         int skipnr, fallback = 0;
  53
  54         if (type) {
  55                 /* Depending on error type, find different stack entries. */
  56                 switch (*type) {
  57                 case KFENCE_ERROR_UAF:
  58                 case KFENCE_ERROR_OOB:
  59                 case KFENCE_ERROR_INVALID:
  60                         /*
  61                          * kfence_handle_page_fault() may be called with pt_regs
  62                          * set to NULL; in that case we'll simply show the full
  63                          * stack trace.
  64                          */
  65                         return 0;
  66                 case KFENCE_ERROR_CORRUPTION:
  67                 case KFENCE_ERROR_INVALID_FREE:
  68                         break;
  69                 }
  70         }
  71
  72         for (skipnr = 0; skipnr < num_entries; skipnr++) {
  73                 int len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skipnr]);
  74
  75                 if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfence_") ||
  76                     str_has_prefix(buf, ARCH_FUNC_PREFIX "__kfence_") ||
  77                     !strncmp(buf, ARCH_FUNC_PREFIX "__slab_free", len)) {
  78                         /*
  79                          * In case of tail calls from any of the below
  80                          * to any of the above.
  81                          */
  82                         fallback = skipnr + 1;
  83                 }
  84
  85                 /* Also the *_bulk() variants by only checking prefixes. */
  86                 if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfree") ||
  87                     str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_free") ||
  88                     str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmalloc") ||
  89                     str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_alloc"))
  90                         goto found;
  91         }
  92         if (fallback < num_entries)
  93                 return fallback;
  94 found:
  95         skipnr++;
  96         return skipnr < num_entries ? skipnr : 0;
  97 }
  98
  99 static void kfence_print_stack(struct seq_file *seq, const struct kfence_metadata *meta,
 100                                bool show_alloc)
 101 {
 102         const struct kfence_track *track = show_alloc ? &meta->alloc_track : &meta->free_track;
 103
 104         if (track->num_stack_entries) {
 105                 /* Skip allocation/free internals stack. */
 106                 int i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL);
 107
 108                 /* stack_trace_seq_print() does not exist; open code our own. */
 109                 for (; i < track->num_stack_entries; i++)
 110                         seq_con_printf(seq, " %pS\n", (void *)track->stack_entries[i]);
 111         } else {
 112                 seq_con_printf(seq, " no %s stack\n", show_alloc ? "allocation" : "deallocation");
 113         }
 114 }
 115
 116 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta)
 117 {
 118         const int size = abs(meta->size);
 119         const unsigned long start = meta->addr;
 120         const struct kmem_cache *const cache = meta->cache;
 121
 122         lockdep_assert_held(&meta->lock);
 123
 124         if (meta->state == KFENCE_OBJECT_UNUSED) {
 125                 seq_con_printf(seq, "kfence-#%td unused\n", meta - kfence_metadata);
 126                 return;
 127         }
 128
 129         seq_con_printf(seq,
 130                        "kfence-#%td [0x%p-0x%p"
 131                        ", size=%d, cache=%s] allocated by task %d:\n",
 132                        meta - kfence_metadata, (void *)start, (void *)(start + size - 1), size,
 133                        (cache && cache->name) ? cache->name : "<destroyed>", meta->alloc_track.pid);
 134         kfence_print_stack(seq, meta, true);
 135
 136         if (meta->state == KFENCE_OBJECT_FREED) {
 137                 seq_con_printf(seq, "\nfreed by task %d:\n", meta->free_track.pid);
 138                 kfence_print_stack(seq, meta, false);
 139         }
 140 }
 141
 142 /*
 143  * Show bytes at @addr that are different from the expected canary values, up to
 144  * @max_bytes.
 145  */
 146 static void print_diff_canary(unsigned long address, size_t bytes_to_show,
 147                               const struct kfence_metadata *meta)
 148 {
 149         const unsigned long show_until_addr = address + bytes_to_show;
 150         const u8 *cur, *end;
 151
 152         /* Do not show contents of object nor read into following guard page. */
 153         end = (const u8 *)(address < meta->addr ? min(show_until_addr, meta->addr)
 154                                                 : min(show_until_addr, PAGE_ALIGN(address)));
 155
 156         pr_cont("[");
 157         for (cur = (const u8 *)address; cur < end; cur++) {
 158                 if (*cur == KFENCE_CANARY_PATTERN(cur))
 159                         pr_cont(" .");
 160                 else if (no_hash_pointers)
 161                         pr_cont(" 0x%02x", *cur);
 162                 else /* Do not leak kernel memory in non-debug builds. */
 163                         pr_cont(" !");
 164         }
 165         pr_cont(" ]");
 166 }
 167
 168 static const char *get_access_type(bool is_write)
 169 {
 170         return is_write ? "write" : "read";
 171 }
 172
 173 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
 174                          const struct kfence_metadata *meta, enum kfence_error_type type)
 175 {
 176         unsigned long stack_entries[KFENCE_STACK_DEPTH] = { 0 };
 177         const ptrdiff_t object_index = meta ? meta - kfence_metadata : -1;
 178         int num_stack_entries;
 179         int skipnr = 0;
 180
 181         if (regs) {
 182                 num_stack_entries = stack_trace_save_regs(regs, stack_entries, KFENCE_STACK_DEPTH, 0);
 183         } else {
 184                 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 1);
 185                 skipnr = get_stack_skipnr(stack_entries, num_stack_entries, &type);
 186         }
 187
 188         /* Require non-NULL meta, except if KFENCE_ERROR_INVALID. */
 189         if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta))
 190                 return;
 191
 192         if (meta)
 193                 lockdep_assert_held(&meta->lock);
 194         /*
 195          * Because we may generate reports in printk-unfriendly parts of the
 196          * kernel, such as scheduler code, the use of printk() could deadlock.
 197          * Until such time that all printing code here is safe in all parts of
 198          * the kernel, accept the risk, and just get our message out (given the
 199          * system might already behave unpredictably due to the memory error).
 200          * As such, also disable lockdep to hide warnings, and avoid disabling
 201          * lockdep for the rest of the kernel.
 202          */
 203         lockdep_off();
 204
 205         pr_err("==================================================================\n");
 206         /* Print report header. */
 207         switch (type) {
 208         case KFENCE_ERROR_OOB: {
 209                 const bool left_of_object = address < meta->addr;
 210
 211                 pr_err("BUG: KFENCE: out-of-bounds %s in %pS\n\n", get_access_type(is_write),
 212                        (void *)stack_entries[skipnr]);
 213                 pr_err("Out-of-bounds %s at 0x%p (%luB %s of kfence-#%td):\n",
 214                        get_access_type(is_write), (void *)address,
 215                        left_of_object ? meta->addr - address : address - meta->addr,
 216                        left_of_object ? "left" : "right", object_index);
 217                 break;
 218         }
 219         case KFENCE_ERROR_UAF:
 220                 pr_err("BUG: KFENCE: use-after-free %s in %pS\n\n", get_access_type(is_write),
 221                        (void *)stack_entries[skipnr]);
 222                 pr_err("Use-after-free %s at 0x%p (in kfence-#%td):\n",
 223                        get_access_type(is_write), (void *)address, object_index);
 224                 break;
 225         case KFENCE_ERROR_CORRUPTION:
 226                 pr_err("BUG: KFENCE: memory corruption in %pS\n\n", (void *)stack_entries[skipnr]);
 227                 pr_err("Corrupted memory at 0x%p ", (void *)address);
 228                 print_diff_canary(address, 16, meta);
 229                 pr_cont(" (in kfence-#%td):\n", object_index);
 230                 break;
 231         case KFENCE_ERROR_INVALID:
 232                 pr_err("BUG: KFENCE: invalid %s in %pS\n\n", get_access_type(is_write),
 233                        (void *)stack_entries[skipnr]);
 234                 pr_err("Invalid %s at 0x%p:\n", get_access_type(is_write),
 235                        (void *)address);
 236                 break;
 237         case KFENCE_ERROR_INVALID_FREE:
 238                 pr_err("BUG: KFENCE: invalid free in %pS\n\n", (void *)stack_entries[skipnr]);
 239                 pr_err("Invalid free of 0x%p (in kfence-#%td):\n", (void *)address,
 240                        object_index);
 241                 break;
 242         }
 243
 244         /* Print stack trace and object info. */
 245         stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0);
 246
 247         if (meta) {
 248                 pr_err("\n");
 249                 kfence_print_object(NULL, meta);
 250         }
 251
 252         /* Print report footer. */
 253         pr_err("\n");
 254         if (no_hash_pointers && regs)
 255                 show_regs(regs);
 256         else
 257                 dump_stack_print_info(KERN_ERR);
 258         trace_error_report_end(ERROR_DETECTOR_KFENCE, address);
 259         pr_err("==================================================================\n");
 260
 261         lockdep_on();
 262
 263         if (panic_on_warn)
 264                 panic("panic_on_warn set ...\n");
 265
 266         /* We encountered a memory unsafety error, taint the kernel! */
 267         add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK);
 268 }