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 extern raw_spinlock_t kfence_freelist_lock; 38 39 /* KFENCE object states. */ 40 enum kfence_object_state { 41 KFENCE_OBJECT_UNUSED, /* Object is unused. */ 42 KFENCE_OBJECT_ALLOCATED, /* Object is currently allocated. */ 43 KFENCE_OBJECT_RCU_FREEING, /* Object was allocated, and then being freed by rcu. */ 44 KFENCE_OBJECT_FREED, /* Object was allocated, and then freed. */ 45 }; 46 47 /* Alloc/free tracking information. */ 48 struct kfence_track { 49 pid_t pid; 50 int cpu; 51 u64 ts_nsec; 52 int num_stack_entries; 53 unsigned long stack_entries[KFENCE_STACK_DEPTH]; 54 }; 55 56 /* KFENCE metadata per guarded allocation. */ 57 struct kfence_metadata { 58 struct list_head list __guarded_by(&kfence_freelist_lock); /* Freelist node. */ 59 struct rcu_head rcu_head; /* For delayed freeing. */ 60 61 /* 62 * Lock protecting below data; to ensure consistency of the below data, 63 * since the following may execute concurrently: __kfence_alloc(), 64 * __kfence_free(), kfence_handle_page_fault(). However, note that we 65 * cannot grab the same metadata off the freelist twice, and multiple 66 * __kfence_alloc() cannot run concurrently on the same metadata. 67 */ 68 raw_spinlock_t lock; 69 70 /* The current state of the object; see above. */ 71 enum kfence_object_state state; 72 73 /* 74 * Allocated object address; cannot be calculated from size, because of 75 * alignment requirements. 76 * 77 * Invariant: ALIGN_DOWN(addr, PAGE_SIZE) is constant. 78 */ 79 unsigned long addr; 80 81 /* 82 * The size of the original allocation. 83 */ 84 size_t size; 85 86 /* 87 * The kmem_cache cache of the last allocation; NULL if never allocated 88 * or the cache has already been destroyed. 89 */ 90 struct kmem_cache *cache; 91 92 /* 93 * In case of an invalid access, the page that was unprotected; we 94 * optimistically only store one address. 95 */ 96 unsigned long unprotected_page __guarded_by(&lock); 97 98 /* Allocation and free stack information. */ 99 struct kfence_track alloc_track __guarded_by(&lock); 100 struct kfence_track free_track __guarded_by(&lock); 101 /* For updating alloc_covered on frees. */ 102 u32 alloc_stack_hash __guarded_by(&lock); 103 #ifdef CONFIG_MEMCG 104 struct slabobj_ext obj_exts; 105 #endif 106 }; 107 108 #define KFENCE_METADATA_SIZE PAGE_ALIGN(sizeof(struct kfence_metadata) * \ 109 CONFIG_KFENCE_NUM_OBJECTS) 110 111 extern struct kfence_metadata *kfence_metadata; 112 113 static inline struct kfence_metadata *addr_to_metadata(unsigned long addr) 114 { 115 long index; 116 117 /* The checks do not affect performance; only called from slow-paths. */ 118 119 if (!is_kfence_address((void *)addr)) 120 return NULL; 121 122 /* 123 * May be an invalid index if called with an address at the edge of 124 * __kfence_pool, in which case we would report an "invalid access" 125 * error. 126 */ 127 index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1; 128 if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS) 129 return NULL; 130 131 return &kfence_metadata[index]; 132 } 133 134 /* KFENCE error types for report generation. */ 135 enum kfence_error_type { 136 KFENCE_ERROR_OOB, /* Detected a out-of-bounds access. */ 137 KFENCE_ERROR_UAF, /* Detected a use-after-free access. */ 138 KFENCE_ERROR_CORRUPTION, /* Detected a memory corruption on free. */ 139 KFENCE_ERROR_INVALID, /* Invalid access of unknown type. */ 140 KFENCE_ERROR_INVALID_FREE, /* Invalid free. */ 141 }; 142 143 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs, 144 const struct kfence_metadata *meta, enum kfence_error_type type); 145 146 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta) __must_hold(&meta->lock); 147 148 #endif /* MM_KFENCE_KFENCE_H */ 149