mm/kmsan/report.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * KMSAN error reporting routines.
   4  *
   5  * Copyright (C) 2019-2022 Google LLC
   6  * Author: Alexander Potapenko <glider@google.com>
   7  *
   8  */
   9
  10 #include <linux/console.h>
  11 #include <linux/moduleparam.h>
  12 #include <linux/stackdepot.h>
  13 #include <linux/stacktrace.h>
  14 #include <linux/uaccess.h>
  15
  16 #include "kmsan.h"
  17
  18 static DEFINE_RAW_SPINLOCK(kmsan_report_lock);
  19 #define DESCR_SIZE 128
  20 /* Protected by kmsan_report_lock */
  21 static char report_local_descr[DESCR_SIZE];
  22 int panic_on_kmsan __read_mostly;
  23
  24 #ifdef MODULE_PARAM_PREFIX
  25 #undef MODULE_PARAM_PREFIX
  26 #endif
  27 #define MODULE_PARAM_PREFIX "kmsan."
  28 module_param_named(panic, panic_on_kmsan, int, 0);
  29
  30 /*
  31  * Skip internal KMSAN frames.
  32  */
  33 static int get_stack_skipnr(const unsigned long stack_entries[],
  34                             int num_entries)
  35 {
  36         int len, skip;
  37         char buf[64];
  38
  39         for (skip = 0; skip < num_entries; ++skip) {
  40                 len = scnprintf(buf, sizeof(buf), "%ps",
  41                                 (void *)stack_entries[skip]);
  42
  43                 /* Never show __msan_* or kmsan_* functions. */
  44                 if ((strnstr(buf, "__msan_", len) == buf) ||
  45                     (strnstr(buf, "kmsan_", len) == buf))
  46                         continue;
  47
  48                 /*
  49                  * No match for runtime functions -- @skip entries to skip to
  50                  * get to first frame of interest.
  51                  */
  52                 break;
  53         }
  54
  55         return skip;
  56 }
  57
  58 /*
  59  * Currently the descriptions of locals generated by Clang look as follows:
  60  *   ----local_name@function_name
  61  * We want to print only the name of the local, as other information in that
  62  * description can be confusing.
  63  * The meaningful part of the description is copied to a global buffer to avoid
  64  * allocating memory.
  65  */
  66 static char *pretty_descr(char *descr)
  67 {
  68         int pos = 0, len = strlen(descr);
  69
  70         for (int i = 0; i < len; i++) {
  71                 if (descr[i] == '@')
  72                         break;
  73                 if (descr[i] == '-')
  74                         continue;
  75                 report_local_descr[pos] = descr[i];
  76                 if (pos + 1 == DESCR_SIZE)
  77                         break;
  78                 pos++;
  79         }
  80         report_local_descr[pos] = 0;
  81         return report_local_descr;
  82 }
  83
  84 void kmsan_print_origin(depot_stack_handle_t origin)
  85 {
  86         unsigned long *entries = NULL, *chained_entries = NULL;
  87         unsigned int nr_entries, chained_nr_entries, skipnr;
  88         void *pc1 = NULL, *pc2 = NULL;
  89         depot_stack_handle_t head;
  90         unsigned long magic;
  91         char *descr = NULL;
  92         unsigned int depth;
  93
  94         if (!origin)
  95                 return;
  96
  97         while (true) {
  98                 nr_entries = stack_depot_fetch(origin, &entries);
  99                 depth = kmsan_depth_from_eb(stack_depot_get_extra_bits(origin));
 100                 magic = nr_entries ? entries[0] : 0;
 101                 if ((nr_entries == 4) && (magic == KMSAN_ALLOCA_MAGIC_ORIGIN)) {
 102                         descr = (char *)entries[1];
 103                         pc1 = (void *)entries[2];
 104                         pc2 = (void *)entries[3];
 105                         pr_err("Local variable %s created at:\n",
 106                                pretty_descr(descr));
 107                         if (pc1)
 108                                 pr_err(" %pSb\n", pc1);
 109                         if (pc2)
 110                                 pr_err(" %pSb\n", pc2);
 111                         break;
 112                 }
 113                 if ((nr_entries == 3) && (magic == KMSAN_CHAIN_MAGIC_ORIGIN)) {
 114                         /*
 115                          * Origin chains deeper than KMSAN_MAX_ORIGIN_DEPTH are
 116                          * not stored, so the output may be incomplete.
 117                          */
 118                         if (depth == KMSAN_MAX_ORIGIN_DEPTH)
 119                                 pr_err("<Zero or more stacks not recorded to save memory>\n\n");
 120                         head = entries[1];
 121                         origin = entries[2];
 122                         pr_err("Uninit was stored to memory at:\n");
 123                         chained_nr_entries =
 124                                 stack_depot_fetch(head, &chained_entries);
 125                         kmsan_internal_unpoison_memory(
 126                                 chained_entries,
 127                                 chained_nr_entries * sizeof(*chained_entries),
 128                                 /*checked*/ false);
 129                         skipnr = get_stack_skipnr(chained_entries,
 130                                                   chained_nr_entries);
 131                         stack_trace_print(chained_entries + skipnr,
 132                                           chained_nr_entries - skipnr, 0);
 133                         pr_err("\n");
 134                         continue;
 135                 }
 136                 pr_err("Uninit was created at:\n");
 137                 if (nr_entries) {
 138                         skipnr = get_stack_skipnr(entries, nr_entries);
 139                         stack_trace_print(entries + skipnr, nr_entries - skipnr,
 140                                           0);
 141                 } else {
 142                         pr_err("(stack is not available)\n");
 143                 }
 144                 break;
 145         }
 146 }
 147
 148 void kmsan_report(depot_stack_handle_t origin, void *address, int size,
 149                   int off_first, int off_last, const void *user_addr,
 150                   enum kmsan_bug_reason reason)
 151 {
 152         unsigned long stack_entries[KMSAN_STACK_DEPTH];
 153         int num_stack_entries, skipnr;
 154         char *bug_type = NULL;
 155         unsigned long ua_flags;
 156         bool is_uaf;
 157
 158         if (!kmsan_enabled)
 159                 return;
 160         if (!current->kmsan_ctx.allow_reporting)
 161                 return;
 162         if (!origin)
 163                 return;
 164
 165         current->kmsan_ctx.allow_reporting = false;
 166         ua_flags = user_access_save();
 167         raw_spin_lock(&kmsan_report_lock);
 168         pr_err("=====================================================\n");
 169         is_uaf = kmsan_uaf_from_eb(stack_depot_get_extra_bits(origin));
 170         switch (reason) {
 171         case REASON_ANY:
 172                 bug_type = is_uaf ? "use-after-free" : "uninit-value";
 173                 break;
 174         case REASON_COPY_TO_USER:
 175                 bug_type = is_uaf ? "kernel-infoleak-after-free" :
 176                                     "kernel-infoleak";
 177                 break;
 178         case REASON_SUBMIT_URB:
 179                 bug_type = is_uaf ? "kernel-usb-infoleak-after-free" :
 180                                     "kernel-usb-infoleak";
 181                 break;
 182         }
 183
 184         num_stack_entries =
 185                 stack_trace_save(stack_entries, KMSAN_STACK_DEPTH, 1);
 186         skipnr = get_stack_skipnr(stack_entries, num_stack_entries);
 187
 188         pr_err("BUG: KMSAN: %s in %pSb\n", bug_type,
 189                (void *)stack_entries[skipnr]);
 190         stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
 191                           0);
 192         pr_err("\n");
 193
 194         kmsan_print_origin(origin);
 195
 196         if (size) {
 197                 pr_err("\n");
 198                 if (off_first == off_last)
 199                         pr_err("Byte %d of %d is uninitialized\n", off_first,
 200                                size);
 201                 else
 202                         pr_err("Bytes %d-%d of %d are uninitialized\n",
 203                                off_first, off_last, size);
 204         }
 205         if (address)
 206                 pr_err("Memory access of size %d starts at %px\n", size,
 207                        address);
 208         if (user_addr && reason == REASON_COPY_TO_USER)
 209                 pr_err("Data copied to user address %px\n", user_addr);
 210         pr_err("\n");
 211         dump_stack_print_info(KERN_ERR);
 212         pr_err("=====================================================\n");
 213         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 214         raw_spin_unlock(&kmsan_report_lock);
 215         if (panic_on_kmsan)
 216                 panic("kmsan.panic set ...\n");
 217         user_access_restore(ua_flags);
 218         current->kmsan_ctx.allow_reporting = true;
 219 }