1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * Kernel Electric-Fence (KFENCE). For more info please see 4 * Documentation/dev-tools/kfence.rst. 5 * 6 * Copyright (C) 2020, Google LLC. 7 */ 8 9 #ifndef MM_KFENCE_KFENCE_H 10 #define MM_KFENCE_KFENCE_H 11 12 #include <linux/mm.h> 13 #include <linux/slab.h> 14 #include <linux/spinlock.h> 15 #include <linux/types.h> 16 17 #include "../slab.h" /* for struct kmem_cache */ 18 19 /* 20 * Get the canary byte pattern for @addr. Use a pattern that varies based on the 21 * lower 3 bits of the address, to detect memory corruptions with higher 22 * probability, where similar constants are used. 23 */ 24 #define KFENCE_CANARY_PATTERN_U8(addr) ((u8)0xaa ^ (u8)((unsigned long)(addr) & 0x7)) 25 26 /* 27 * Define a continuous 8-byte canary starting from a multiple of 8. The canary 28 * of each byte is only related to the lowest three bits of its address, so the 29 * canary of every 8 bytes is the same. 64-bit memory can be filled and checked 30 * at a time instead of byte by byte to improve performance. 31 */ 32 #define KFENCE_CANARY_PATTERN_U64 ((u64)0xaaaaaaaaaaaaaaaa ^ (u64)(0x0706050403020100)) 33 34 /* Maximum stack depth for reports. */ 35 #define KFENCE_STACK_DEPTH 64 36 37 /* KFENCE object states. */ 38 enum kfence_object_state { 39 KFENCE_OBJECT_UNUSED, /* Object is unused. */ 40 KFENCE_OBJECT_ALLOCATED, /* Object is currently allocated. */ 41 KFENCE_OBJECT_FREED, /* Object was allocated, and then freed. */ 42 }; 43 44 /* Alloc/free tracking information. */ 45 struct kfence_track { 46 pid_t pid; 47 int cpu; 48 u64 ts_nsec; 49 int num_stack_entries; 50 unsigned long stack_entries[KFENCE_STACK_DEPTH]; 51 }; 52 53 /* KFENCE metadata per guarded allocation. */ 54 struct kfence_metadata { 55 struct list_head list; /* Freelist node; access under kfence_freelist_lock. */ 56 struct rcu_head rcu_head; /* For delayed freeing. */ 57 58 /* 59 * Lock protecting below data; to ensure consistency of the below data, 60 * since the following may execute concurrently: __kfence_alloc(), 61 * __kfence_free(), kfence_handle_page_fault(). However, note that we 62 * cannot grab the same metadata off the freelist twice, and multiple 63 * __kfence_alloc() cannot run concurrently on the same metadata. 64 */ 65 raw_spinlock_t lock; 66 67 /* The current state of the object; see above. */ 68 enum kfence_object_state state; 69 70 /* 71 * Allocated object address; cannot be calculated from size, because of 72 * alignment requirements. 73 * 74 * Invariant: ALIGN_DOWN(addr, PAGE_SIZE) is constant. 75 */ 76 unsigned long addr; 77 78 /* 79 * The size of the original allocation. 80 */ 81 size_t size; 82 83 /* 84 * The kmem_cache cache of the last allocation; NULL if never allocated 85 * or the cache has already been destroyed. 86 */ 87 struct kmem_cache *cache; 88 89 /* 90 * In case of an invalid access, the page that was unprotected; we 91 * optimistically only store one address. 92 */ 93 unsigned long unprotected_page; 94 95 /* Allocation and free stack information. */ 96 struct kfence_track alloc_track; 97 struct kfence_track free_track; 98 /* For updating alloc_covered on frees. */ 99 u32 alloc_stack_hash; 100 #ifdef CONFIG_MEMCG 101 struct obj_cgroup *objcg; 102 #endif 103 }; 104 105 extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS]; 106 107 static inline struct kfence_metadata *addr_to_metadata(unsigned long addr) 108 { 109 long index; 110 111 /* The checks do not affect performance; only called from slow-paths. */ 112 113 if (!is_kfence_address((void *)addr)) 114 return NULL; 115 116 /* 117 * May be an invalid index if called with an address at the edge of 118 * __kfence_pool, in which case we would report an "invalid access" 119 * error. 120 */ 121 index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1; 122 if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS) 123 return NULL; 124 125 return &kfence_metadata[index]; 126 } 127 128 /* KFENCE error types for report generation. */ 129 enum kfence_error_type { 130 KFENCE_ERROR_OOB, /* Detected a out-of-bounds access. */ 131 KFENCE_ERROR_UAF, /* Detected a use-after-free access. */ 132 KFENCE_ERROR_CORRUPTION, /* Detected a memory corruption on free. */ 133 KFENCE_ERROR_INVALID, /* Invalid access of unknown type. */ 134 KFENCE_ERROR_INVALID_FREE, /* Invalid free. */ 135 }; 136 137 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs, 138 const struct kfence_metadata *meta, enum kfence_error_type type); 139 140 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta); 141 142 #endif /* MM_KFENCE_KFENCE_H */ 143