mm/kasan/tags.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This file contains common tag-based KASAN code.
   4  *
   5  * Copyright (c) 2018 Google, Inc.
   6  * Copyright (c) 2020 Google, Inc.
   7  */
   8
   9 #include <linux/atomic.h>
  10 #include <linux/init.h>
  11 #include <linux/kasan.h>
  12 #include <linux/kernel.h>
  13 #include <linux/memblock.h>
  14 #include <linux/memory.h>
  15 #include <linux/mm.h>
  16 #include <linux/stackdepot.h>
  17 #include <linux/static_key.h>
  18 #include <linux/string.h>
  19 #include <linux/types.h>
  20
  21 #include "kasan.h"
  22 #include "../slab.h"
  23
  24 #define KASAN_STACK_RING_SIZE_DEFAULT (32 << 10)
  25
  26 enum kasan_arg_stacktrace {
  27         KASAN_ARG_STACKTRACE_DEFAULT,
  28         KASAN_ARG_STACKTRACE_OFF,
  29         KASAN_ARG_STACKTRACE_ON,
  30 };
  31
  32 static enum kasan_arg_stacktrace kasan_arg_stacktrace __initdata;
  33
  34 /* Whether to collect alloc/free stack traces. */
  35 DEFINE_STATIC_KEY_TRUE(kasan_flag_stacktrace);
  36
  37 /* Non-zero, as initial pointer values are 0. */
  38 #define STACK_RING_BUSY_PTR ((void *)1)
  39
  40 struct kasan_stack_ring stack_ring = {
  41         .lock = __RW_LOCK_UNLOCKED(stack_ring.lock)
  42 };
  43
  44 /* kasan.stacktrace=off/on */
  45 static int __init early_kasan_flag_stacktrace(char *arg)
  46 {
  47         if (!arg)
  48                 return -EINVAL;
  49
  50         if (!strcmp(arg, "off"))
  51                 kasan_arg_stacktrace = KASAN_ARG_STACKTRACE_OFF;
  52         else if (!strcmp(arg, "on"))
  53                 kasan_arg_stacktrace = KASAN_ARG_STACKTRACE_ON;
  54         else
  55                 return -EINVAL;
  56
  57         return 0;
  58 }
  59 early_param("kasan.stacktrace", early_kasan_flag_stacktrace);
  60
  61 /* kasan.stack_ring_size=<number of entries> */
  62 static int __init early_kasan_flag_stack_ring_size(char *arg)
  63 {
  64         if (!arg)
  65                 return -EINVAL;
  66
  67         return kstrtoul(arg, 0, &stack_ring.size);
  68 }
  69 early_param("kasan.stack_ring_size", early_kasan_flag_stack_ring_size);
  70
  71 void __init kasan_init_tags(void)
  72 {
  73         switch (kasan_arg_stacktrace) {
  74         case KASAN_ARG_STACKTRACE_DEFAULT:
  75                 /* Default is specified by kasan_flag_stacktrace definition. */
  76                 break;
  77         case KASAN_ARG_STACKTRACE_OFF:
  78                 static_branch_disable(&kasan_flag_stacktrace);
  79                 break;
  80         case KASAN_ARG_STACKTRACE_ON:
  81                 static_branch_enable(&kasan_flag_stacktrace);
  82                 break;
  83         }
  84
  85         if (kasan_stack_collection_enabled()) {
  86                 if (!stack_ring.size)
  87                         stack_ring.size = KASAN_STACK_RING_SIZE_DEFAULT;
  88                 stack_ring.entries = memblock_alloc(
  89                         sizeof(stack_ring.entries[0]) * stack_ring.size,
  90                         SMP_CACHE_BYTES);
  91                 if (WARN_ON(!stack_ring.entries))
  92                         static_branch_disable(&kasan_flag_stacktrace);
  93         }
  94 }
  95
  96 static void save_stack_info(struct kmem_cache *cache, void *object,
  97                         gfp_t gfp_flags, bool is_free)
  98 {
  99         unsigned long flags;
 100         depot_stack_handle_t stack, old_stack;
 101         u64 pos;
 102         struct kasan_stack_ring_entry *entry;
 103         void *old_ptr;
 104
 105         stack = kasan_save_stack(gfp_flags,
 106                         STACK_DEPOT_FLAG_CAN_ALLOC | STACK_DEPOT_FLAG_GET);
 107
 108         /*
 109          * Prevent save_stack_info() from modifying stack ring
 110          * when kasan_complete_mode_report_info() is walking it.
 111          */
 112         read_lock_irqsave(&stack_ring.lock, flags);
 113
 114 next:
 115         pos = atomic64_fetch_add(1, &stack_ring.pos);
 116         entry = &stack_ring.entries[pos % stack_ring.size];
 117
 118         /* Detect stack ring entry slots that are being written to. */
 119         old_ptr = READ_ONCE(entry->ptr);
 120         if (old_ptr == STACK_RING_BUSY_PTR)
 121                 goto next; /* Busy slot. */
 122         if (!try_cmpxchg(&entry->ptr, &old_ptr, STACK_RING_BUSY_PTR))
 123                 goto next; /* Busy slot. */
 124
 125         old_stack = entry->stack;
 126
 127         entry->size = cache->object_size;
 128         entry->pid = current->pid;
 129         entry->stack = stack;
 130         entry->is_free = is_free;
 131
 132         entry->ptr = object;
 133
 134         read_unlock_irqrestore(&stack_ring.lock, flags);
 135
 136         if (old_stack)
 137                 stack_depot_put(old_stack);
 138 }
 139
 140 void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
 141 {
 142         save_stack_info(cache, object, flags, false);
 143 }
 144
 145 void kasan_save_free_info(struct kmem_cache *cache, void *object)
 146 {
 147         save_stack_info(cache, object, 0, true);
 148 }