1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * KMSAN compiler API. 4 * 5 * This file implements __msan_XXX hooks that Clang inserts into the code 6 * compiled with -fsanitize=kernel-memory. 7 * See Documentation/dev-tools/kmsan.rst for more information on how KMSAN 8 * instrumentation works. 9 * 10 * Copyright (C) 2017-2022 Google LLC 11 * Author: Alexander Potapenko <glider@google.com> 12 * 13 */ 14 15 #include "kmsan.h" 16 #include <linux/gfp.h> 17 #include <linux/kmsan_string.h> 18 #include <linux/mm.h> 19 #include <linux/uaccess.h> 20 21 static inline bool is_bad_asm_addr(void *addr, uintptr_t size, bool is_store) 22 { 23 if ((u64)addr < TASK_SIZE) 24 return true; 25 if (!kmsan_get_metadata(addr, KMSAN_META_SHADOW)) 26 return true; 27 return false; 28 } 29 30 static inline struct shadow_origin_ptr 31 get_shadow_origin_ptr(void *addr, u64 size, bool store) 32 { 33 unsigned long ua_flags = user_access_save(); 34 struct shadow_origin_ptr ret; 35 36 ret = kmsan_get_shadow_origin_ptr(addr, size, store); 37 user_access_restore(ua_flags); 38 return ret; 39 } 40 41 /* Get shadow and origin pointers for a memory load with non-standard size. */ 42 struct shadow_origin_ptr __msan_metadata_ptr_for_load_n(void *addr, 43 uintptr_t size) 44 { 45 return get_shadow_origin_ptr(addr, size, /*store*/ false); 46 } 47 EXPORT_SYMBOL(__msan_metadata_ptr_for_load_n); 48 49 /* Get shadow and origin pointers for a memory store with non-standard size. */ 50 struct shadow_origin_ptr __msan_metadata_ptr_for_store_n(void *addr, 51 uintptr_t size) 52 { 53 return get_shadow_origin_ptr(addr, size, /*store*/ true); 54 } 55 EXPORT_SYMBOL(__msan_metadata_ptr_for_store_n); 56 57 /* 58 * Declare functions that obtain shadow/origin pointers for loads and stores 59 * with fixed size. 60 */ 61 #define DECLARE_METADATA_PTR_GETTER(size) \ 62 struct shadow_origin_ptr __msan_metadata_ptr_for_load_##size( \ 63 void *addr) \ 64 { \ 65 return get_shadow_origin_ptr(addr, size, /*store*/ false); \ 66 } \ 67 EXPORT_SYMBOL(__msan_metadata_ptr_for_load_##size); \ 68 struct shadow_origin_ptr __msan_metadata_ptr_for_store_##size( \ 69 void *addr) \ 70 { \ 71 return get_shadow_origin_ptr(addr, size, /*store*/ true); \ 72 } \ 73 EXPORT_SYMBOL(__msan_metadata_ptr_for_store_##size) 74 75 DECLARE_METADATA_PTR_GETTER(1); 76 DECLARE_METADATA_PTR_GETTER(2); 77 DECLARE_METADATA_PTR_GETTER(4); 78 DECLARE_METADATA_PTR_GETTER(8); 79 80 /* 81 * Handle a memory store performed by inline assembly. KMSAN conservatively 82 * attempts to unpoison the outputs of asm() directives to prevent false 83 * positives caused by missed stores. 84 */ 85 void __msan_instrument_asm_store(void *addr, uintptr_t size) 86 { 87 unsigned long ua_flags; 88 89 if (!kmsan_enabled || kmsan_in_runtime()) 90 return; 91 92 ua_flags = user_access_save(); 93 /* 94 * Most of the accesses are below 32 bytes. The two exceptions so far 95 * are clwb() (64 bytes) and FPU state (512 bytes). 96 * It's unlikely that the assembly will touch more than 512 bytes. 97 */ 98 if (size > 512) { 99 WARN_ONCE(1, "assembly store size too big: %ld\n", size); 100 size = 8; 101 } 102 if (is_bad_asm_addr(addr, size, /*is_store*/ true)) { 103 user_access_restore(ua_flags); 104 return; 105 } 106 kmsan_enter_runtime(); 107 /* Unpoisoning the memory on best effort. */ 108 kmsan_internal_unpoison_memory(addr, size, /*checked*/ false); 109 kmsan_leave_runtime(); 110 user_access_restore(ua_flags); 111 } 112 EXPORT_SYMBOL(__msan_instrument_asm_store); 113 114 /* 115 * KMSAN instrumentation pass replaces LLVM memcpy, memmove and memset 116 * intrinsics with calls to respective __msan_ functions. We use 117 * get_param0_metadata() and set_retval_metadata() to store the shadow/origin 118 * values for the destination argument of these functions and use them for the 119 * functions' return values. 120 */ 121 static inline void get_param0_metadata(u64 *shadow, 122 depot_stack_handle_t *origin) 123 { 124 struct kmsan_ctx *ctx = kmsan_get_context(); 125 126 *shadow = *(u64 *)(ctx->cstate.param_tls); 127 *origin = ctx->cstate.param_origin_tls[0]; 128 } 129 130 static inline void set_retval_metadata(u64 shadow, depot_stack_handle_t origin) 131 { 132 struct kmsan_ctx *ctx = kmsan_get_context(); 133 134 *(u64 *)(ctx->cstate.retval_tls) = shadow; 135 ctx->cstate.retval_origin_tls = origin; 136 } 137 138 /* Handle llvm.memmove intrinsic. */ 139 void *__msan_memmove(void *dst, const void *src, uintptr_t n) 140 { 141 depot_stack_handle_t origin; 142 void *result; 143 u64 shadow; 144 145 get_param0_metadata(&shadow, &origin); 146 result = __memmove(dst, src, n); 147 if (!n) 148 /* Some people call memmove() with zero length. */ 149 return result; 150 if (!kmsan_enabled || kmsan_in_runtime()) 151 return result; 152 153 kmsan_enter_runtime(); 154 kmsan_internal_memmove_metadata(dst, (void *)src, n); 155 kmsan_leave_runtime(); 156 157 set_retval_metadata(shadow, origin); 158 return result; 159 } 160 EXPORT_SYMBOL(__msan_memmove); 161 162 /* Handle llvm.memcpy intrinsic. */ 163 void *__msan_memcpy(void *dst, const void *src, uintptr_t n) 164 { 165 depot_stack_handle_t origin; 166 void *result; 167 u64 shadow; 168 169 get_param0_metadata(&shadow, &origin); 170 result = __memcpy(dst, src, n); 171 if (!n) 172 /* Some people call memcpy() with zero length. */ 173 return result; 174 175 if (!kmsan_enabled || kmsan_in_runtime()) 176 return result; 177 178 kmsan_enter_runtime(); 179 /* Using memmove instead of memcpy doesn't affect correctness. */ 180 kmsan_internal_memmove_metadata(dst, (void *)src, n); 181 kmsan_leave_runtime(); 182 183 set_retval_metadata(shadow, origin); 184 return result; 185 } 186 EXPORT_SYMBOL(__msan_memcpy); 187 188 /* Handle llvm.memset intrinsic. */ 189 void *__msan_memset(void *dst, int c, uintptr_t n) 190 { 191 depot_stack_handle_t origin; 192 void *result; 193 u64 shadow; 194 195 get_param0_metadata(&shadow, &origin); 196 result = __memset(dst, c, n); 197 if (!kmsan_enabled || kmsan_in_runtime()) 198 return result; 199 200 kmsan_enter_runtime(); 201 /* 202 * Clang doesn't pass parameter metadata here, so it is impossible to 203 * use shadow of @c to set up the shadow for @dst. 204 */ 205 kmsan_internal_unpoison_memory(dst, n, /*checked*/ false); 206 kmsan_leave_runtime(); 207 208 set_retval_metadata(shadow, origin); 209 return result; 210 } 211 EXPORT_SYMBOL(__msan_memset); 212 213 /* 214 * Create a new origin from an old one. This is done when storing an 215 * uninitialized value to memory. When reporting an error, KMSAN unrolls and 216 * prints the whole chain of stores that preceded the use of this value. 217 */ 218 depot_stack_handle_t __msan_chain_origin(depot_stack_handle_t origin) 219 { 220 depot_stack_handle_t ret = 0; 221 unsigned long ua_flags; 222 223 if (!kmsan_enabled || kmsan_in_runtime()) 224 return ret; 225 226 ua_flags = user_access_save(); 227 228 /* Creating new origins may allocate memory. */ 229 kmsan_enter_runtime(); 230 ret = kmsan_internal_chain_origin(origin); 231 kmsan_leave_runtime(); 232 user_access_restore(ua_flags); 233 return ret; 234 } 235 EXPORT_SYMBOL(__msan_chain_origin); 236 237 /* Poison a local variable when entering a function. */ 238 void __msan_poison_alloca(void *address, uintptr_t size, char *descr) 239 { 240 depot_stack_handle_t handle; 241 unsigned long entries[4]; 242 unsigned long ua_flags; 243 244 if (!kmsan_enabled || kmsan_in_runtime()) 245 return; 246 247 ua_flags = user_access_save(); 248 entries[0] = KMSAN_ALLOCA_MAGIC_ORIGIN; 249 entries[1] = (u64)descr; 250 entries[2] = (u64)__builtin_return_address(0); 251 /* 252 * With frame pointers enabled, it is possible to quickly fetch the 253 * second frame of the caller stack without calling the unwinder. 254 * Without them, simply do not bother. 255 */ 256 if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER)) 257 entries[3] = (u64)__builtin_return_address(1); 258 else 259 entries[3] = 0; 260 261 /* stack_depot_save() may allocate memory. */ 262 kmsan_enter_runtime(); 263 handle = stack_depot_save(entries, ARRAY_SIZE(entries), GFP_ATOMIC); 264 kmsan_leave_runtime(); 265 266 kmsan_internal_set_shadow_origin(address, size, -1, handle, 267 /*checked*/ true); 268 user_access_restore(ua_flags); 269 } 270 EXPORT_SYMBOL(__msan_poison_alloca); 271 272 /* Unpoison a local variable. */ 273 void __msan_unpoison_alloca(void *address, uintptr_t size) 274 { 275 if (!kmsan_enabled || kmsan_in_runtime()) 276 return; 277 278 kmsan_enter_runtime(); 279 kmsan_internal_unpoison_memory(address, size, /*checked*/ true); 280 kmsan_leave_runtime(); 281 } 282 EXPORT_SYMBOL(__msan_unpoison_alloca); 283 284 /* 285 * Report that an uninitialized value with the given origin was used in a way 286 * that constituted undefined behavior. 287 */ 288 void __msan_warning(u32 origin) 289 { 290 if (!kmsan_enabled || kmsan_in_runtime()) 291 return; 292 kmsan_enter_runtime(); 293 kmsan_report(origin, /*address*/ 0, /*size*/ 0, 294 /*off_first*/ 0, /*off_last*/ 0, /*user_addr*/ 0, 295 REASON_ANY); 296 kmsan_leave_runtime(); 297 } 298 EXPORT_SYMBOL(__msan_warning); 299 300 /* 301 * At the beginning of an instrumented function, obtain the pointer to 302 * `struct kmsan_context_state` holding the metadata for function parameters. 303 */ 304 struct kmsan_context_state *__msan_get_context_state(void) 305 { 306 return &kmsan_get_context()->cstate; 307 } 308 EXPORT_SYMBOL(__msan_get_context_state); 309