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 <linux/stdarg.h>
   9
  10 #include <linux/kernel.h>
  11 #include <linux/lockdep.h>
  12 #include <linux/math.h>
  13 #include <linux/printk.h>
  14 #include <linux/sched/debug.h>
  15 #include <linux/seq_file.h>
  16 #include <linux/stacktrace.h>
  17 #include <linux/string.h>
  18 #include <trace/events/error_report.h>
  19
  20 #include <asm/kfence.h>
  21
  22 #include "kfence.h"
  23
  24 /* May be overridden by <asm/kfence.h>. */
  25 #ifndef ARCH_FUNC_PREFIX
  26 #define ARCH_FUNC_PREFIX ""
  27 #endif
  28
  29 extern bool no_hash_pointers;
  30
  31 /* Helper function to either print to a seq_file or to console. */
  32 __printf(2, 3)
  33 static void seq_con_printf(struct seq_file *seq, const char *fmt, ...)
  34 {
  35         va_list args;
  36
  37         va_start(args, fmt);
  38         if (seq)
  39                 seq_vprintf(seq, fmt, args);
  40         else
  41                 vprintk(fmt, args);
  42         va_end(args);
  43 }
  44
  45 /*
  46  * Get the number of stack entries to skip to get out of MM internals. @type is
  47  * optional, and if set to NULL, assumes an allocation or free stack.
  48  */
  49 static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries,
  50                             const enum kfence_error_type *type)
  51 {
  52         char buf[64];
  53         int skipnr, fallback = 0;
  54
  55         if (type) {
  56                 /* Depending on error type, find different stack entries. */
  57                 switch (*type) {
  58                 case KFENCE_ERROR_UAF:
  59                 case KFENCE_ERROR_OOB:
  60                 case KFENCE_ERROR_INVALID:
  61                         /*
  62                          * kfence_handle_page_fault() may be called with pt_regs
  63                          * set to NULL; in that case we'll simply show the full
  64                          * stack trace.
  65                          */
  66                         return 0;
  67                 case KFENCE_ERROR_CORRUPTION:
  68                 case KFENCE_ERROR_INVALID_FREE:
  69                         break;
  70                 }
  71         }
  72
  73         for (skipnr = 0; skipnr < num_entries; skipnr++) {
  74                 int len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skipnr]);
  75
  76                 if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfence_") ||
  77                     str_has_prefix(buf, ARCH_FUNC_PREFIX "__kfence_") ||
  78                     !strncmp(buf, ARCH_FUNC_PREFIX "__slab_free", len)) {
  79                         /*
  80                          * In case of tail calls from any of the below
  81                          * to any of the above.
  82                          */
  83                         fallback = skipnr + 1;
  84                 }
  85
  86                 /* Also the *_bulk() variants by only checking prefixes. */
  87                 if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfree") ||
  88                     str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_free") ||
  89                     str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmalloc") ||
  90                     str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_alloc"))
  91                         goto found;
  92         }
  93         if (fallback < num_entries)
  94                 return fallback;
  95 found:
  96         skipnr++;
  97         return skipnr < num_entries ? skipnr : 0;
  98 }
  99
 100 static void kfence_print_stack(struct seq_file *seq, const struct kfence_metadata *meta,
 101                                bool show_alloc)
 102 {
 103         const struct kfence_track *track = show_alloc ? &meta->alloc_track : &meta->free_track;
 104         u64 ts_sec = track->ts_nsec;
 105         unsigned long rem_nsec = do_div(ts_sec, NSEC_PER_SEC);
 106
 107         /* Timestamp matches printk timestamp format. */
 108         seq_con_printf(seq, "%s by task %d on cpu %d at %lu.%06lus:\n",
 109                        show_alloc ? "allocated" : "freed", track->pid,
 110                        track->cpu, (unsigned long)ts_sec, rem_nsec / 1000);
 111
 112         if (track->num_stack_entries) {
 113                 /* Skip allocation/free internals stack. */
 114                 int i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL);
 115
 116                 /* stack_trace_seq_print() does not exist; open code our own. */
 117                 for (; i < track->num_stack_entries; i++)
 118                         seq_con_printf(seq, " %pS\n", (void *)track->stack_entries[i]);
 119         } else {
 120                 seq_con_printf(seq, " no %s stack\n", show_alloc ? "allocation" : "deallocation");
 121         }
 122 }
 123
 124 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta)
 125 {
 126         const int size = abs(meta->size);
 127         const unsigned long start = meta->addr;
 128         const struct kmem_cache *const cache = meta->cache;
 129
 130         lockdep_assert_held(&meta->lock);
 131
 132         if (meta->state == KFENCE_OBJECT_UNUSED) {
 133                 seq_con_printf(seq, "kfence-#%td unused\n", meta - kfence_metadata);
 134                 return;
 135         }
 136
 137         seq_con_printf(seq, "kfence-#%td: 0x%p-0x%p, size=%d, cache=%s\n\n",
 138                        meta - kfence_metadata, (void *)start, (void *)(start + size - 1),
 139                        size, (cache && cache->name) ? cache->name : "<destroyed>");
 140
 141         kfence_print_stack(seq, meta, true);
 142
 143         if (meta->state == KFENCE_OBJECT_FREED) {
 144                 seq_con_printf(seq, "\n");
 145                 kfence_print_stack(seq, meta, false);
 146         }
 147 }
 148
 149 /*
 150  * Show bytes at @addr that are different from the expected canary values, up to
 151  * @max_bytes.
 152  */
 153 static void print_diff_canary(unsigned long address, size_t bytes_to_show,
 154                               const struct kfence_metadata *meta)
 155 {
 156         const unsigned long show_until_addr = address + bytes_to_show;
 157         const u8 *cur, *end;
 158
 159         /* Do not show contents of object nor read into following guard page. */
 160         end = (const u8 *)(address < meta->addr ? min(show_until_addr, meta->addr)
 161                                                 : min(show_until_addr, PAGE_ALIGN(address)));
 162
 163         pr_cont("[");
 164         for (cur = (const u8 *)address; cur < end; cur++) {
 165                 if (*cur == KFENCE_CANARY_PATTERN(cur))
 166                         pr_cont(" .");
 167                 else if (no_hash_pointers)
 168                         pr_cont(" 0x%02x", *cur);
 169                 else /* Do not leak kernel memory in non-debug builds. */
 170                         pr_cont(" !");
 171         }
 172         pr_cont(" ]");
 173 }
 174
 175 static const char *get_access_type(bool is_write)
 176 {
 177         return is_write ? "write" : "read";
 178 }
 179
 180 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
 181                          const struct kfence_metadata *meta, enum kfence_error_type type)
 182 {
 183         unsigned long stack_entries[KFENCE_STACK_DEPTH] = { 0 };
 184         const ptrdiff_t object_index = meta ? meta - kfence_metadata : -1;
 185         int num_stack_entries;
 186         int skipnr = 0;
 187
 188         if (regs) {
 189                 num_stack_entries = stack_trace_save_regs(regs, stack_entries, KFENCE_STACK_DEPTH, 0);
 190         } else {
 191                 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 1);
 192                 skipnr = get_stack_skipnr(stack_entries, num_stack_entries, &type);
 193         }
 194
 195         /* Require non-NULL meta, except if KFENCE_ERROR_INVALID. */
 196         if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta))
 197                 return;
 198
 199         if (meta)
 200                 lockdep_assert_held(&meta->lock);
 201         /*
 202          * Because we may generate reports in printk-unfriendly parts of the
 203          * kernel, such as scheduler code, the use of printk() could deadlock.
 204          * Until such time that all printing code here is safe in all parts of
 205          * the kernel, accept the risk, and just get our message out (given the
 206          * system might already behave unpredictably due to the memory error).
 207          * As such, also disable lockdep to hide warnings, and avoid disabling
 208          * lockdep for the rest of the kernel.
 209          */
 210         lockdep_off();
 211
 212         pr_err("==================================================================\n");
 213         /* Print report header. */
 214         switch (type) {
 215         case KFENCE_ERROR_OOB: {
 216                 const bool left_of_object = address < meta->addr;
 217
 218                 pr_err("BUG: KFENCE: out-of-bounds %s in %pS\n\n", get_access_type(is_write),
 219                        (void *)stack_entries[skipnr]);
 220                 pr_err("Out-of-bounds %s at 0x%p (%luB %s of kfence-#%td):\n",
 221                        get_access_type(is_write), (void *)address,
 222                        left_of_object ? meta->addr - address : address - meta->addr,
 223                        left_of_object ? "left" : "right", object_index);
 224                 break;
 225         }
 226         case KFENCE_ERROR_UAF:
 227                 pr_err("BUG: KFENCE: use-after-free %s in %pS\n\n", get_access_type(is_write),
 228                        (void *)stack_entries[skipnr]);
 229                 pr_err("Use-after-free %s at 0x%p (in kfence-#%td):\n",
 230                        get_access_type(is_write), (void *)address, object_index);
 231                 break;
 232         case KFENCE_ERROR_CORRUPTION:
 233                 pr_err("BUG: KFENCE: memory corruption in %pS\n\n", (void *)stack_entries[skipnr]);
 234                 pr_err("Corrupted memory at 0x%p ", (void *)address);
 235                 print_diff_canary(address, 16, meta);
 236                 pr_cont(" (in kfence-#%td):\n", object_index);
 237                 break;
 238         case KFENCE_ERROR_INVALID:
 239                 pr_err("BUG: KFENCE: invalid %s in %pS\n\n", get_access_type(is_write),
 240                        (void *)stack_entries[skipnr]);
 241                 pr_err("Invalid %s at 0x%p:\n", get_access_type(is_write),
 242                        (void *)address);
 243                 break;
 244         case KFENCE_ERROR_INVALID_FREE:
 245                 pr_err("BUG: KFENCE: invalid free in %pS\n\n", (void *)stack_entries[skipnr]);
 246                 pr_err("Invalid free of 0x%p (in kfence-#%td):\n", (void *)address,
 247                        object_index);
 248                 break;
 249         }
 250
 251         /* Print stack trace and object info. */
 252         stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0);
 253
 254         if (meta) {
 255                 pr_err("\n");
 256                 kfence_print_object(NULL, meta);
 257         }
 258
 259         /* Print report footer. */
 260         pr_err("\n");
 261         if (no_hash_pointers && regs)
 262                 show_regs(regs);
 263         else
 264                 dump_stack_print_info(KERN_ERR);
 265         trace_error_report_end(ERROR_DETECTOR_KFENCE, address);
 266         pr_err("==================================================================\n");
 267
 268         lockdep_on();
 269
 270         if (panic_on_warn)
 271                 panic("panic_on_warn set ...\n");
 272
 273         /* We encountered a memory safety error, taint the kernel! */
 274         add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK);
 275 }