mm/kasan/tags.c

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