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
is_bad_asm_addr(void * addr,uintptr_t size,bool is_store)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
get_shadow_origin_ptr(void * addr,u64 size,bool store)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 /*
42 * KMSAN instrumentation functions follow. They are not declared elsewhere in
43 * the kernel code, so they are preceded by prototypes, to silence
44 * -Wmissing-prototypes warnings.
45 */
46
47 /* Get shadow and origin pointers for a memory load with non-standard size. */
48 struct shadow_origin_ptr __msan_metadata_ptr_for_load_n(void *addr,
49 uintptr_t size);
__msan_metadata_ptr_for_load_n(void * addr,uintptr_t size)50 struct shadow_origin_ptr __msan_metadata_ptr_for_load_n(void *addr,
51 uintptr_t size)
52 {
53 return get_shadow_origin_ptr(addr, size, /*store*/ false);
54 }
55 EXPORT_SYMBOL(__msan_metadata_ptr_for_load_n);
56
57 /* Get shadow and origin pointers for a memory store with non-standard size. */
58 struct shadow_origin_ptr __msan_metadata_ptr_for_store_n(void *addr,
59 uintptr_t size);
__msan_metadata_ptr_for_store_n(void * addr,uintptr_t size)60 struct shadow_origin_ptr __msan_metadata_ptr_for_store_n(void *addr,
61 uintptr_t size)
62 {
63 return get_shadow_origin_ptr(addr, size, /*store*/ true);
64 }
65 EXPORT_SYMBOL(__msan_metadata_ptr_for_store_n);
66
67 /*
68 * Declare functions that obtain shadow/origin pointers for loads and stores
69 * with fixed size.
70 */
71 #define DECLARE_METADATA_PTR_GETTER(size) \
72 struct shadow_origin_ptr __msan_metadata_ptr_for_load_##size( \
73 void *addr); \
74 struct shadow_origin_ptr __msan_metadata_ptr_for_load_##size( \
75 void *addr) \
76 { \
77 return get_shadow_origin_ptr(addr, size, /*store*/ false); \
78 } \
79 EXPORT_SYMBOL(__msan_metadata_ptr_for_load_##size); \
80 struct shadow_origin_ptr __msan_metadata_ptr_for_store_##size( \
81 void *addr); \
82 struct shadow_origin_ptr __msan_metadata_ptr_for_store_##size( \
83 void *addr) \
84 { \
85 return get_shadow_origin_ptr(addr, size, /*store*/ true); \
86 } \
87 EXPORT_SYMBOL(__msan_metadata_ptr_for_store_##size)
88
89 DECLARE_METADATA_PTR_GETTER(1);
90 DECLARE_METADATA_PTR_GETTER(2);
91 DECLARE_METADATA_PTR_GETTER(4);
92 DECLARE_METADATA_PTR_GETTER(8);
93
94 /*
95 * Handle a memory store performed by inline assembly. KMSAN conservatively
96 * attempts to unpoison the outputs of asm() directives to prevent false
97 * positives caused by missed stores.
98 *
99 * __msan_instrument_asm_store() may be called for inline assembly code when
100 * entering or leaving IRQ. We omit the check for kmsan_in_runtime() to ensure
101 * the memory written to in these cases is also marked as initialized.
102 */
103 void __msan_instrument_asm_store(void *addr, uintptr_t size);
__msan_instrument_asm_store(void * addr,uintptr_t size)104 void __msan_instrument_asm_store(void *addr, uintptr_t size)
105 {
106 unsigned long ua_flags;
107
108 if (!kmsan_enabled)
109 return;
110
111 ua_flags = user_access_save();
112 /*
113 * Most of the accesses are below 32 bytes. The two exceptions so far
114 * are clwb() (64 bytes) and FPU state (512 bytes).
115 * It's unlikely that the assembly will touch more than 512 bytes.
116 */
117 if (size > 512) {
118 WARN_ONCE(1, "assembly store size too big: %ld\n", size);
119 size = 8;
120 }
121 if (is_bad_asm_addr(addr, size, /*is_store*/ true)) {
122 user_access_restore(ua_flags);
123 return;
124 }
125 /* Unpoisoning the memory on best effort. */
126 kmsan_internal_unpoison_memory(addr, size, /*checked*/ false);
127 user_access_restore(ua_flags);
128 }
129 EXPORT_SYMBOL(__msan_instrument_asm_store);
130
131 /*
132 * KMSAN instrumentation pass replaces LLVM memcpy, memmove and memset
133 * intrinsics with calls to respective __msan_ functions. We use
134 * get_param0_metadata() and set_retval_metadata() to store the shadow/origin
135 * values for the destination argument of these functions and use them for the
136 * functions' return values.
137 */
get_param0_metadata(u64 * shadow,depot_stack_handle_t * origin)138 static inline void get_param0_metadata(u64 *shadow,
139 depot_stack_handle_t *origin)
140 {
141 struct kmsan_ctx *ctx = kmsan_get_context();
142
143 *shadow = *(u64 *)(ctx->cstate.param_tls);
144 *origin = ctx->cstate.param_origin_tls[0];
145 }
146
set_retval_metadata(u64 shadow,depot_stack_handle_t origin)147 static inline void set_retval_metadata(u64 shadow, depot_stack_handle_t origin)
148 {
149 struct kmsan_ctx *ctx = kmsan_get_context();
150
151 *(u64 *)(ctx->cstate.retval_tls) = shadow;
152 ctx->cstate.retval_origin_tls = origin;
153 }
154
155 /* Handle llvm.memmove intrinsic. */
156 void *__msan_memmove(void *dst, const void *src, uintptr_t n);
__msan_memmove(void * dst,const void * src,uintptr_t n)157 void *__msan_memmove(void *dst, const void *src, uintptr_t n)
158 {
159 depot_stack_handle_t origin;
160 void *result;
161 u64 shadow;
162
163 get_param0_metadata(&shadow, &origin);
164 result = __memmove(dst, src, n);
165 if (!n)
166 /* Some people call memmove() with zero length. */
167 return result;
168 if (!kmsan_enabled || kmsan_in_runtime())
169 return result;
170
171 kmsan_enter_runtime();
172 kmsan_internal_memmove_metadata(dst, (void *)src, n);
173 kmsan_leave_runtime();
174
175 set_retval_metadata(shadow, origin);
176 return result;
177 }
178 EXPORT_SYMBOL(__msan_memmove);
179
180 /* Handle llvm.memcpy intrinsic. */
181 void *__msan_memcpy(void *dst, const void *src, uintptr_t n);
__msan_memcpy(void * dst,const void * src,uintptr_t n)182 void *__msan_memcpy(void *dst, const void *src, uintptr_t n)
183 {
184 depot_stack_handle_t origin;
185 void *result;
186 u64 shadow;
187
188 get_param0_metadata(&shadow, &origin);
189 result = __memcpy(dst, src, n);
190 if (!n)
191 /* Some people call memcpy() with zero length. */
192 return result;
193
194 if (!kmsan_enabled || kmsan_in_runtime())
195 return result;
196
197 kmsan_enter_runtime();
198 /* Using memmove instead of memcpy doesn't affect correctness. */
199 kmsan_internal_memmove_metadata(dst, (void *)src, n);
200 kmsan_leave_runtime();
201
202 set_retval_metadata(shadow, origin);
203 return result;
204 }
205 EXPORT_SYMBOL(__msan_memcpy);
206
207 /* Handle llvm.memset intrinsic. */
208 void *__msan_memset(void *dst, int c, uintptr_t n);
__msan_memset(void * dst,int c,uintptr_t n)209 void *__msan_memset(void *dst, int c, uintptr_t n)
210 {
211 depot_stack_handle_t origin;
212 void *result;
213 u64 shadow;
214
215 get_param0_metadata(&shadow, &origin);
216 result = __memset(dst, c, n);
217 if (!kmsan_enabled || kmsan_in_runtime())
218 return result;
219
220 kmsan_enter_runtime();
221 /*
222 * Clang doesn't pass parameter metadata here, so it is impossible to
223 * use shadow of @c to set up the shadow for @dst.
224 */
225 kmsan_internal_unpoison_memory(dst, n, /*checked*/ false);
226 kmsan_leave_runtime();
227
228 set_retval_metadata(shadow, origin);
229 return result;
230 }
231 EXPORT_SYMBOL(__msan_memset);
232
233 /*
234 * Create a new origin from an old one. This is done when storing an
235 * uninitialized value to memory. When reporting an error, KMSAN unrolls and
236 * prints the whole chain of stores that preceded the use of this value.
237 */
238 depot_stack_handle_t __msan_chain_origin(depot_stack_handle_t origin);
__msan_chain_origin(depot_stack_handle_t origin)239 depot_stack_handle_t __msan_chain_origin(depot_stack_handle_t origin)
240 {
241 depot_stack_handle_t ret = 0;
242 unsigned long ua_flags;
243
244 if (!kmsan_enabled || kmsan_in_runtime())
245 return ret;
246
247 ua_flags = user_access_save();
248
249 /* Creating new origins may allocate memory. */
250 kmsan_enter_runtime();
251 ret = kmsan_internal_chain_origin(origin);
252 kmsan_leave_runtime();
253 user_access_restore(ua_flags);
254 return ret;
255 }
256 EXPORT_SYMBOL(__msan_chain_origin);
257
258 /* Poison a local variable when entering a function. */
259 void __msan_poison_alloca(void *address, uintptr_t size, char *descr);
__msan_poison_alloca(void * address,uintptr_t size,char * descr)260 void __msan_poison_alloca(void *address, uintptr_t size, char *descr)
261 {
262 depot_stack_handle_t handle;
263 unsigned long entries[4];
264 unsigned long ua_flags;
265
266 if (!kmsan_enabled || kmsan_in_runtime())
267 return;
268
269 ua_flags = user_access_save();
270 entries[0] = KMSAN_ALLOCA_MAGIC_ORIGIN;
271 entries[1] = (u64)descr;
272 entries[2] = (u64)__builtin_return_address(0);
273 /*
274 * With frame pointers enabled, it is possible to quickly fetch the
275 * second frame of the caller stack without calling the unwinder.
276 * Without them, simply do not bother.
277 */
278 if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER))
279 entries[3] = (u64)__builtin_return_address(1);
280 else
281 entries[3] = 0;
282
283 /* stack_depot_save() may allocate memory. */
284 kmsan_enter_runtime();
285 handle = stack_depot_save(entries, ARRAY_SIZE(entries), __GFP_HIGH);
286 kmsan_leave_runtime();
287
288 kmsan_internal_set_shadow_origin(address, size, -1, handle,
289 /*checked*/ true);
290 user_access_restore(ua_flags);
291 }
292 EXPORT_SYMBOL(__msan_poison_alloca);
293
294 /* Unpoison a local variable. */
295 void __msan_unpoison_alloca(void *address, uintptr_t size);
__msan_unpoison_alloca(void * address,uintptr_t size)296 void __msan_unpoison_alloca(void *address, uintptr_t size)
297 {
298 if (!kmsan_enabled || kmsan_in_runtime())
299 return;
300
301 kmsan_enter_runtime();
302 kmsan_internal_unpoison_memory(address, size, /*checked*/ true);
303 kmsan_leave_runtime();
304 }
305 EXPORT_SYMBOL(__msan_unpoison_alloca);
306
307 /*
308 * Report that an uninitialized value with the given origin was used in a way
309 * that constituted undefined behavior.
310 */
311 void __msan_warning(u32 origin);
__msan_warning(u32 origin)312 void __msan_warning(u32 origin)
313 {
314 if (!kmsan_enabled || kmsan_in_runtime())
315 return;
316 kmsan_enter_runtime();
317 kmsan_report(origin, /*address*/ 0, /*size*/ 0,
318 /*off_first*/ 0, /*off_last*/ 0, /*user_addr*/ 0,
319 REASON_ANY);
320 kmsan_leave_runtime();
321 }
322 EXPORT_SYMBOL(__msan_warning);
323
324 /*
325 * At the beginning of an instrumented function, obtain the pointer to
326 * `struct kmsan_context_state` holding the metadata for function parameters.
327 */
328 struct kmsan_context_state *__msan_get_context_state(void);
__msan_get_context_state(void)329 struct kmsan_context_state *__msan_get_context_state(void)
330 {
331 return &kmsan_get_context()->cstate;
332 }
333 EXPORT_SYMBOL(__msan_get_context_state);
334