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)(le64_to_cpu(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_RCU_FREEING, /* Object was allocated, and then being freed by rcu. */ 42 KFENCE_OBJECT_FREED, /* Object was allocated, and then freed. */ 43 }; 44 45 /* Alloc/free tracking information. */ 46 struct kfence_track { 47 pid_t pid; 48 int cpu; 49 u64 ts_nsec; 50 int num_stack_entries; 51 unsigned long stack_entries[KFENCE_STACK_DEPTH]; 52 }; 53 54 /* KFENCE metadata per guarded allocation. */ 55 struct kfence_metadata { 56 struct list_head list; /* Freelist node; access under kfence_freelist_lock. */ 57 struct rcu_head rcu_head; /* For delayed freeing. */ 58 59 /* 60 * Lock protecting below data; to ensure consistency of the below data, 61 * since the following may execute concurrently: __kfence_alloc(), 62 * __kfence_free(), kfence_handle_page_fault(). However, note that we 63 * cannot grab the same metadata off the freelist twice, and multiple 64 * __kfence_alloc() cannot run concurrently on the same metadata. 65 */ 66 raw_spinlock_t lock; 67 68 /* The current state of the object; see above. */ 69 enum kfence_object_state state; 70 71 /* 72 * Allocated object address; cannot be calculated from size, because of 73 * alignment requirements. 74 * 75 * Invariant: ALIGN_DOWN(addr, PAGE_SIZE) is constant. 76 */ 77 unsigned long addr; 78 79 /* 80 * The size of the original allocation. 81 */ 82 size_t size; 83 84 /* 85 * The kmem_cache cache of the last allocation; NULL if never allocated 86 * or the cache has already been destroyed. 87 */ 88 struct kmem_cache *cache; 89 90 /* 91 * In case of an invalid access, the page that was unprotected; we 92 * optimistically only store one address. 93 */ 94 unsigned long unprotected_page; 95 96 /* Allocation and free stack information. */ 97 struct kfence_track alloc_track; 98 struct kfence_track free_track; 99 /* For updating alloc_covered on frees. */ 100 u32 alloc_stack_hash; 101 #ifdef CONFIG_MEMCG 102 struct slabobj_ext obj_exts; 103 #endif 104 }; 105 106 #define KFENCE_METADATA_SIZE PAGE_ALIGN(sizeof(struct kfence_metadata) * \ 107 CONFIG_KFENCE_NUM_OBJECTS) 108 109 extern struct kfence_metadata *kfence_metadata; 110 111 static inline struct kfence_metadata *addr_to_metadata(unsigned long addr) 112 { 113 long index; 114 115 /* The checks do not affect performance; only called from slow-paths. */ 116 117 if (!is_kfence_address((void *)addr)) 118 return NULL; 119 120 /* 121 * May be an invalid index if called with an address at the edge of 122 * __kfence_pool, in which case we would report an "invalid access" 123 * error. 124 */ 125 index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1; 126 if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS) 127 return NULL; 128 129 return &kfence_metadata[index]; 130 } 131 132 /* KFENCE error types for report generation. */ 133 enum kfence_error_type { 134 KFENCE_ERROR_OOB, /* Detected a out-of-bounds access. */ 135 KFENCE_ERROR_UAF, /* Detected a use-after-free access. */ 136 KFENCE_ERROR_CORRUPTION, /* Detected a memory corruption on free. */ 137 KFENCE_ERROR_INVALID, /* Invalid access of unknown type. */ 138 KFENCE_ERROR_INVALID_FREE, /* Invalid free. */ 139 }; 140 141 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs, 142 const struct kfence_metadata *meta, enum kfence_error_type type); 143 144 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta); 145 146 #endif /* MM_KFENCE_KFENCE_H */ 147