1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * This file contains core hardware tag-based KASAN code.
4 *
5 * Copyright (c) 2020 Google, Inc.
6 * Author: Andrey Konovalov <andreyknvl@google.com>
7 */
8
9 #define pr_fmt(fmt) "kasan: " fmt
10
11 #include <linux/init.h>
12 #include <linux/kasan.h>
13 #include <linux/kernel.h>
14 #include <linux/memory.h>
15 #include <linux/mm.h>
16 #include <linux/static_key.h>
17 #include <linux/string.h>
18 #include <linux/types.h>
19
20 #include "kasan.h"
21
22 enum kasan_arg {
23 KASAN_ARG_DEFAULT,
24 KASAN_ARG_OFF,
25 KASAN_ARG_ON,
26 };
27
28 enum kasan_arg_mode {
29 KASAN_ARG_MODE_DEFAULT,
30 KASAN_ARG_MODE_SYNC,
31 KASAN_ARG_MODE_ASYNC,
32 KASAN_ARG_MODE_ASYMM,
33 };
34
35 enum kasan_arg_vmalloc {
36 KASAN_ARG_VMALLOC_DEFAULT,
37 KASAN_ARG_VMALLOC_OFF,
38 KASAN_ARG_VMALLOC_ON,
39 };
40
41 static enum kasan_arg kasan_arg __ro_after_init;
42 static enum kasan_arg_mode kasan_arg_mode __ro_after_init;
43 static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata;
44
45 /*
46 * Whether KASAN is enabled at all.
47 * The value remains false until KASAN is initialized by kasan_init_hw_tags().
48 */
49 DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled);
50 EXPORT_SYMBOL(kasan_flag_enabled);
51
52 /*
53 * Whether the selected mode is synchronous, asynchronous, or asymmetric.
54 * Defaults to KASAN_MODE_SYNC.
55 */
56 enum kasan_mode kasan_mode __ro_after_init;
57 EXPORT_SYMBOL_GPL(kasan_mode);
58
59 /* Whether to enable vmalloc tagging. */
60 DEFINE_STATIC_KEY_TRUE(kasan_flag_vmalloc);
61
62 #define PAGE_ALLOC_SAMPLE_DEFAULT 1
63 #define PAGE_ALLOC_SAMPLE_ORDER_DEFAULT 3
64
65 /*
66 * Sampling interval of page_alloc allocation (un)poisoning.
67 * Defaults to no sampling.
68 */
69 unsigned long kasan_page_alloc_sample = PAGE_ALLOC_SAMPLE_DEFAULT;
70
71 /*
72 * Minimum order of page_alloc allocations to be affected by sampling.
73 * The default value is chosen to match both
74 * PAGE_ALLOC_COSTLY_ORDER and SKB_FRAG_PAGE_ORDER.
75 */
76 unsigned int kasan_page_alloc_sample_order = PAGE_ALLOC_SAMPLE_ORDER_DEFAULT;
77
78 DEFINE_PER_CPU(long, kasan_page_alloc_skip);
79
80 /* kasan=off/on */
early_kasan_flag(char * arg)81 static int __init early_kasan_flag(char *arg)
82 {
83 if (!arg)
84 return -EINVAL;
85
86 if (!strcmp(arg, "off"))
87 kasan_arg = KASAN_ARG_OFF;
88 else if (!strcmp(arg, "on"))
89 kasan_arg = KASAN_ARG_ON;
90 else
91 return -EINVAL;
92
93 return 0;
94 }
95 early_param("kasan", early_kasan_flag);
96
97 /* kasan.mode=sync/async/asymm */
early_kasan_mode(char * arg)98 static int __init early_kasan_mode(char *arg)
99 {
100 if (!arg)
101 return -EINVAL;
102
103 if (!strcmp(arg, "sync"))
104 kasan_arg_mode = KASAN_ARG_MODE_SYNC;
105 else if (!strcmp(arg, "async"))
106 kasan_arg_mode = KASAN_ARG_MODE_ASYNC;
107 else if (!strcmp(arg, "asymm"))
108 kasan_arg_mode = KASAN_ARG_MODE_ASYMM;
109 else
110 return -EINVAL;
111
112 return 0;
113 }
114 early_param("kasan.mode", early_kasan_mode);
115
116 /* kasan.vmalloc=off/on */
early_kasan_flag_vmalloc(char * arg)117 static int __init early_kasan_flag_vmalloc(char *arg)
118 {
119 if (!arg)
120 return -EINVAL;
121
122 if (!strcmp(arg, "off"))
123 kasan_arg_vmalloc = KASAN_ARG_VMALLOC_OFF;
124 else if (!strcmp(arg, "on"))
125 kasan_arg_vmalloc = KASAN_ARG_VMALLOC_ON;
126 else
127 return -EINVAL;
128
129 return 0;
130 }
131 early_param("kasan.vmalloc", early_kasan_flag_vmalloc);
132
kasan_mode_info(void)133 static inline const char *kasan_mode_info(void)
134 {
135 if (kasan_mode == KASAN_MODE_ASYNC)
136 return "async";
137 else if (kasan_mode == KASAN_MODE_ASYMM)
138 return "asymm";
139 else
140 return "sync";
141 }
142
143 /* kasan.page_alloc.sample=<sampling interval> */
early_kasan_flag_page_alloc_sample(char * arg)144 static int __init early_kasan_flag_page_alloc_sample(char *arg)
145 {
146 int rv;
147
148 if (!arg)
149 return -EINVAL;
150
151 rv = kstrtoul(arg, 0, &kasan_page_alloc_sample);
152 if (rv)
153 return rv;
154
155 if (!kasan_page_alloc_sample || kasan_page_alloc_sample > LONG_MAX) {
156 kasan_page_alloc_sample = PAGE_ALLOC_SAMPLE_DEFAULT;
157 return -EINVAL;
158 }
159
160 return 0;
161 }
162 early_param("kasan.page_alloc.sample", early_kasan_flag_page_alloc_sample);
163
164 /* kasan.page_alloc.sample.order=<minimum page order> */
early_kasan_flag_page_alloc_sample_order(char * arg)165 static int __init early_kasan_flag_page_alloc_sample_order(char *arg)
166 {
167 int rv;
168
169 if (!arg)
170 return -EINVAL;
171
172 rv = kstrtouint(arg, 0, &kasan_page_alloc_sample_order);
173 if (rv)
174 return rv;
175
176 if (kasan_page_alloc_sample_order > INT_MAX) {
177 kasan_page_alloc_sample_order = PAGE_ALLOC_SAMPLE_ORDER_DEFAULT;
178 return -EINVAL;
179 }
180
181 return 0;
182 }
183 early_param("kasan.page_alloc.sample.order", early_kasan_flag_page_alloc_sample_order);
184
185 /*
186 * kasan_init_hw_tags_cpu() is called for each CPU.
187 * Not marked as __init as a CPU can be hot-plugged after boot.
188 */
kasan_init_hw_tags_cpu(void)189 void kasan_init_hw_tags_cpu(void)
190 {
191 /*
192 * There's no need to check that the hardware is MTE-capable here,
193 * as this function is only called for MTE-capable hardware.
194 */
195
196 /*
197 * If KASAN is disabled via command line, don't initialize it.
198 * When this function is called, kasan_flag_enabled is not yet
199 * set by kasan_init_hw_tags(). Thus, check kasan_arg instead.
200 */
201 if (kasan_arg == KASAN_ARG_OFF)
202 return;
203
204 /*
205 * Enable async or asymm modes only when explicitly requested
206 * through the command line.
207 */
208 kasan_enable_hw_tags();
209 }
210
211 /* kasan_init_hw_tags() is called once on boot CPU. */
kasan_init_hw_tags(void)212 void __init kasan_init_hw_tags(void)
213 {
214 /* If hardware doesn't support MTE, don't initialize KASAN. */
215 if (!system_supports_mte())
216 return;
217
218 /* If KASAN is disabled via command line, don't initialize it. */
219 if (kasan_arg == KASAN_ARG_OFF)
220 return;
221
222 switch (kasan_arg_mode) {
223 case KASAN_ARG_MODE_DEFAULT:
224 /* Default is specified by kasan_mode definition. */
225 break;
226 case KASAN_ARG_MODE_SYNC:
227 kasan_mode = KASAN_MODE_SYNC;
228 break;
229 case KASAN_ARG_MODE_ASYNC:
230 kasan_mode = KASAN_MODE_ASYNC;
231 break;
232 case KASAN_ARG_MODE_ASYMM:
233 kasan_mode = KASAN_MODE_ASYMM;
234 break;
235 }
236
237 switch (kasan_arg_vmalloc) {
238 case KASAN_ARG_VMALLOC_DEFAULT:
239 /* Default is specified by kasan_flag_vmalloc definition. */
240 break;
241 case KASAN_ARG_VMALLOC_OFF:
242 static_branch_disable(&kasan_flag_vmalloc);
243 break;
244 case KASAN_ARG_VMALLOC_ON:
245 static_branch_enable(&kasan_flag_vmalloc);
246 break;
247 }
248
249 kasan_init_tags();
250
251 /* KASAN is now initialized, enable it. */
252 static_branch_enable(&kasan_flag_enabled);
253
254 pr_info("KernelAddressSanitizer initialized (hw-tags, mode=%s, vmalloc=%s, stacktrace=%s)\n",
255 kasan_mode_info(),
256 kasan_vmalloc_enabled() ? "on" : "off",
257 kasan_stack_collection_enabled() ? "on" : "off");
258 }
259
260 #ifdef CONFIG_KASAN_VMALLOC
261
unpoison_vmalloc_pages(const void * addr,u8 tag)262 static void unpoison_vmalloc_pages(const void *addr, u8 tag)
263 {
264 struct vm_struct *area;
265 int i;
266
267 /*
268 * As hardware tag-based KASAN only tags VM_ALLOC vmalloc allocations
269 * (see the comment in __kasan_unpoison_vmalloc), all of the pages
270 * should belong to a single area.
271 */
272 area = find_vm_area((void *)addr);
273 if (WARN_ON(!area))
274 return;
275
276 for (i = 0; i < area->nr_pages; i++) {
277 struct page *page = area->pages[i];
278
279 page_kasan_tag_set(page, tag);
280 }
281 }
282
init_vmalloc_pages(const void * start,unsigned long size)283 static void init_vmalloc_pages(const void *start, unsigned long size)
284 {
285 const void *addr;
286
287 for (addr = start; addr < start + size; addr += PAGE_SIZE) {
288 struct page *page = vmalloc_to_page(addr);
289
290 clear_highpage_kasan_tagged(page);
291 }
292 }
293
__kasan_unpoison_vmalloc(const void * start,unsigned long size,kasan_vmalloc_flags_t flags)294 void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
295 kasan_vmalloc_flags_t flags)
296 {
297 u8 tag;
298 unsigned long redzone_start, redzone_size;
299
300 if (!kasan_vmalloc_enabled()) {
301 if (flags & KASAN_VMALLOC_INIT)
302 init_vmalloc_pages(start, size);
303 return (void *)start;
304 }
305
306 /*
307 * Don't tag non-VM_ALLOC mappings, as:
308 *
309 * 1. Unlike the software KASAN modes, hardware tag-based KASAN only
310 * supports tagging physical memory. Therefore, it can only tag a
311 * single mapping of normal physical pages.
312 * 2. Hardware tag-based KASAN can only tag memory mapped with special
313 * mapping protection bits, see arch_vmap_pgprot_tagged().
314 * As non-VM_ALLOC mappings can be mapped outside of vmalloc code,
315 * providing these bits would require tracking all non-VM_ALLOC
316 * mappers.
317 *
318 * Thus, for VM_ALLOC mappings, hardware tag-based KASAN only tags
319 * the first virtual mapping, which is created by vmalloc().
320 * Tagging the page_alloc memory backing that vmalloc() allocation is
321 * skipped, see ___GFP_SKIP_KASAN.
322 *
323 * For non-VM_ALLOC allocations, page_alloc memory is tagged as usual.
324 */
325 if (!(flags & KASAN_VMALLOC_VM_ALLOC)) {
326 WARN_ON(flags & KASAN_VMALLOC_INIT);
327 return (void *)start;
328 }
329
330 /*
331 * Don't tag executable memory.
332 * The kernel doesn't tolerate having the PC register tagged.
333 */
334 if (!(flags & KASAN_VMALLOC_PROT_NORMAL)) {
335 WARN_ON(flags & KASAN_VMALLOC_INIT);
336 return (void *)start;
337 }
338
339 tag = kasan_random_tag();
340 start = set_tag(start, tag);
341
342 /* Unpoison and initialize memory up to size. */
343 kasan_unpoison(start, size, flags & KASAN_VMALLOC_INIT);
344
345 /*
346 * Explicitly poison and initialize the in-page vmalloc() redzone.
347 * Unlike software KASAN modes, hardware tag-based KASAN doesn't
348 * unpoison memory when populating shadow for vmalloc() space.
349 */
350 redzone_start = round_up((unsigned long)start + size,
351 KASAN_GRANULE_SIZE);
352 redzone_size = round_up(redzone_start, PAGE_SIZE) - redzone_start;
353 kasan_poison((void *)redzone_start, redzone_size, KASAN_TAG_INVALID,
354 flags & KASAN_VMALLOC_INIT);
355
356 /*
357 * Set per-page tag flags to allow accessing physical memory for the
358 * vmalloc() mapping through page_address(vmalloc_to_page()).
359 */
360 unpoison_vmalloc_pages(start, tag);
361
362 return (void *)start;
363 }
364
__kasan_poison_vmalloc(const void * start,unsigned long size)365 void __kasan_poison_vmalloc(const void *start, unsigned long size)
366 {
367 /*
368 * No tagging here.
369 * The physical pages backing the vmalloc() allocation are poisoned
370 * through the usual page_alloc paths.
371 */
372 }
373
374 #endif
375
kasan_enable_hw_tags(void)376 void kasan_enable_hw_tags(void)
377 {
378 if (kasan_arg_mode == KASAN_ARG_MODE_ASYNC)
379 hw_enable_tag_checks_async();
380 else if (kasan_arg_mode == KASAN_ARG_MODE_ASYMM)
381 hw_enable_tag_checks_asymm();
382 else
383 hw_enable_tag_checks_sync();
384 }
385
386 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
387
388 EXPORT_SYMBOL_GPL(kasan_enable_hw_tags);
389
kasan_force_async_fault(void)390 void kasan_force_async_fault(void)
391 {
392 hw_force_async_tag_fault();
393 }
394 EXPORT_SYMBOL_GPL(kasan_force_async_fault);
395
396 #endif
397