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); 162