root/mm/kasan/tags.c

DEFINITIONS

1. kasan_init_tags
2. random_tag
3. kasan_reset_tag
4. check_memory_region
5. __hwasan_loadN_noabort
6. __hwasan_storeN_noabort
7. __hwasan_tag_memory

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This file contains core tag-based KASAN code.
   4  *
   5  * Copyright (c) 2018 Google, Inc.
   6  * Author: Andrey Konovalov <andreyknvl@google.com>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11  *
  12  */
  13 
  14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  15 
  16 #include <linux/export.h>
  17 #include <linux/interrupt.h>
  18 #include <linux/init.h>
  19 #include <linux/kasan.h>
  20 #include <linux/kernel.h>
  21 #include <linux/kmemleak.h>
  22 #include <linux/linkage.h>
  23 #include <linux/memblock.h>
  24 #include <linux/memory.h>
  25 #include <linux/mm.h>
  26 #include <linux/module.h>
  27 #include <linux/printk.h>
  28 #include <linux/random.h>
  29 #include <linux/sched.h>
  30 #include <linux/sched/task_stack.h>
  31 #include <linux/slab.h>
  32 #include <linux/stacktrace.h>
  33 #include <linux/string.h>
  34 #include <linux/types.h>
  35 #include <linux/vmalloc.h>
  36 #include <linux/bug.h>
  37 
  38 #include "kasan.h"
  39 #include "../slab.h"
  40 
  41 static DEFINE_PER_CPU(u32, prng_state);
  42 
  43 void kasan_init_tags(void)
  44 {
  45         int cpu;
  46 
  47         for_each_possible_cpu(cpu)
  48                 per_cpu(prng_state, cpu) = (u32)get_cycles();
  49 }
  50 
  51 /*
  52  * If a preemption happens between this_cpu_read and this_cpu_write, the only
  53  * side effect is that we'll give a few allocated in different contexts objects
  54  * the same tag. Since tag-based KASAN is meant to be used a probabilistic
  55  * bug-detection debug feature, this doesn't have significant negative impact.
  56  *
  57  * Ideally the tags use strong randomness to prevent any attempts to predict
  58  * them during explicit exploit attempts. But strong randomness is expensive,
  59  * and we did an intentional trade-off to use a PRNG. This non-atomic RMW
  60  * sequence has in fact positive effect, since interrupts that randomly skew
  61  * PRNG at unpredictable points do only good.
  62  */
  63 u8 random_tag(void)
  64 {
  65         u32 state = this_cpu_read(prng_state);
  66 
  67         state = 1664525 * state + 1013904223;
  68         this_cpu_write(prng_state, state);
  69 
  70         return (u8)(state % (KASAN_TAG_MAX + 1));
  71 }
  72 
  73 void *kasan_reset_tag(const void *addr)
  74 {
  75         return reset_tag(addr);
  76 }
  77 
  78 bool check_memory_region(unsigned long addr, size_t size, bool write,
  79                                 unsigned long ret_ip)
  80 {
  81         u8 tag;
  82         u8 *shadow_first, *shadow_last, *shadow;
  83         void *untagged_addr;
  84 
  85         if (unlikely(size == 0))
  86                 return true;
  87 
  88         tag = get_tag((const void *)addr);
  89 
  90         /*
  91          * Ignore accesses for pointers tagged with 0xff (native kernel
  92          * pointer tag) to suppress false positives caused by kmap.
  93          *
  94          * Some kernel code was written to account for archs that don't keep
  95          * high memory mapped all the time, but rather map and unmap particular
  96          * pages when needed. Instead of storing a pointer to the kernel memory,
  97          * this code saves the address of the page structure and offset within
  98          * that page for later use. Those pages are then mapped and unmapped
  99          * with kmap/kunmap when necessary and virt_to_page is used to get the
 100          * virtual address of the page. For arm64 (that keeps the high memory
 101          * mapped all the time), kmap is turned into a page_address call.
 102 
 103          * The issue is that with use of the page_address + virt_to_page
 104          * sequence the top byte value of the original pointer gets lost (gets
 105          * set to KASAN_TAG_KERNEL (0xFF)).
 106          */
 107         if (tag == KASAN_TAG_KERNEL)
 108                 return true;
 109 
 110         untagged_addr = reset_tag((const void *)addr);
 111         if (unlikely(untagged_addr <
 112                         kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
 113                 kasan_report(addr, size, write, ret_ip);
 114                 return false;
 115         }
 116         shadow_first = kasan_mem_to_shadow(untagged_addr);
 117         shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
 118         for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
 119                 if (*shadow != tag) {
 120                         kasan_report(addr, size, write, ret_ip);
 121                         return false;
 122                 }
 123         }
 124 
 125         return true;
 126 }
 127 
 128 #define DEFINE_HWASAN_LOAD_STORE(size)                                  \
 129         void __hwasan_load##size##_noabort(unsigned long addr)          \
 130         {                                                               \
 131                 check_memory_region(addr, size, false, _RET_IP_);       \
 132         }                                                               \
 133         EXPORT_SYMBOL(__hwasan_load##size##_noabort);                   \
 134         void __hwasan_store##size##_noabort(unsigned long addr)         \
 135         {                                                               \
 136                 check_memory_region(addr, size, true, _RET_IP_);        \
 137         }                                                               \
 138         EXPORT_SYMBOL(__hwasan_store##size##_noabort)
 139 
 140 DEFINE_HWASAN_LOAD_STORE(1);
 141 DEFINE_HWASAN_LOAD_STORE(2);
 142 DEFINE_HWASAN_LOAD_STORE(4);
 143 DEFINE_HWASAN_LOAD_STORE(8);
 144 DEFINE_HWASAN_LOAD_STORE(16);
 145 
 146 void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
 147 {
 148         check_memory_region(addr, size, false, _RET_IP_);
 149 }
 150 EXPORT_SYMBOL(__hwasan_loadN_noabort);
 151 
 152 void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
 153 {
 154         check_memory_region(addr, size, true, _RET_IP_);
 155 }
 156 EXPORT_SYMBOL(__hwasan_storeN_noabort);
 157 
 158 void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
 159 {
 160         kasan_poison_shadow((void *)addr, size, tag);
 161 }
 162 EXPORT_SYMBOL(__hwasan_tag_memory);