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 bool 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 true; 88 89 if (unlikely(addr + size < addr)) 90 return !kasan_report(addr, size, write, ret_ip); 91 92 tag = get_tag((const void *)addr); 93 94 /* 95 * Ignore accesses for pointers tagged with 0xff (native kernel 96 * pointer tag) to suppress false positives caused by kmap. 97 * 98 * Some kernel code was written to account for archs that don't keep 99 * high memory mapped all the time, but rather map and unmap particular 100 * pages when needed. Instead of storing a pointer to the kernel memory, 101 * this code saves the address of the page structure and offset within 102 * that page for later use. Those pages are then mapped and unmapped 103 * with kmap/kunmap when necessary and virt_to_page is used to get the 104 * virtual address of the page. For arm64 (that keeps the high memory 105 * mapped all the time), kmap is turned into a page_address call. 106 107 * The issue is that with use of the page_address + virt_to_page 108 * sequence the top byte value of the original pointer gets lost (gets 109 * set to KASAN_TAG_KERNEL (0xFF)). 110 */ 111 if (tag == KASAN_TAG_KERNEL) 112 return true; 113 114 untagged_addr = reset_tag((const void *)addr); 115 if (unlikely(untagged_addr < 116 kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) { 117 return !kasan_report(addr, size, write, ret_ip); 118 } 119 shadow_first = kasan_mem_to_shadow(untagged_addr); 120 shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1); 121 for (shadow = shadow_first; shadow <= shadow_last; shadow++) { 122 if (*shadow != tag) { 123 return !kasan_report(addr, size, write, ret_ip); 124 } 125 } 126 127 return true; 128 } 129 130 #define DEFINE_HWASAN_LOAD_STORE(size) \ 131 void __hwasan_load##size##_noabort(unsigned long addr) \ 132 { \ 133 check_memory_region(addr, size, false, _RET_IP_); \ 134 } \ 135 EXPORT_SYMBOL(__hwasan_load##size##_noabort); \ 136 void __hwasan_store##size##_noabort(unsigned long addr) \ 137 { \ 138 check_memory_region(addr, size, true, _RET_IP_); \ 139 } \ 140 EXPORT_SYMBOL(__hwasan_store##size##_noabort) 141 142 DEFINE_HWASAN_LOAD_STORE(1); 143 DEFINE_HWASAN_LOAD_STORE(2); 144 DEFINE_HWASAN_LOAD_STORE(4); 145 DEFINE_HWASAN_LOAD_STORE(8); 146 DEFINE_HWASAN_LOAD_STORE(16); 147 148 void __hwasan_loadN_noabort(unsigned long addr, unsigned long size) 149 { 150 check_memory_region(addr, size, false, _RET_IP_); 151 } 152 EXPORT_SYMBOL(__hwasan_loadN_noabort); 153 154 void __hwasan_storeN_noabort(unsigned long addr, unsigned long size) 155 { 156 check_memory_region(addr, size, true, _RET_IP_); 157 } 158 EXPORT_SYMBOL(__hwasan_storeN_noabort); 159 160 void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size) 161 { 162 kasan_poison_shadow((void *)addr, size, tag); 163 } 164 EXPORT_SYMBOL(__hwasan_tag_memory); 165