1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * KFENCE reporting.
4 *
5 * Copyright (C) 2020, Google LLC.
6 */
7
8 #include <linux/stdarg.h>
9
10 #include <linux/kernel.h>
11 #include <linux/lockdep.h>
12 #include <linux/math.h>
13 #include <linux/printk.h>
14 #include <linux/sched/debug.h>
15 #include <linux/seq_file.h>
16 #include <linux/stacktrace.h>
17 #include <linux/string.h>
18 #include <trace/events/error_report.h>
19
20 #include <asm/kfence.h>
21
22 #include "kfence.h"
23
24 /* May be overridden by <asm/kfence.h>. */
25 #ifndef ARCH_FUNC_PREFIX
26 #define ARCH_FUNC_PREFIX ""
27 #endif
28
29 extern bool no_hash_pointers;
30
31 /* Helper function to either print to a seq_file or to console. */
32 __printf(2, 3)
seq_con_printf(struct seq_file * seq,const char * fmt,...)33 static void seq_con_printf(struct seq_file *seq, const char *fmt, ...)
34 {
35 va_list args;
36
37 va_start(args, fmt);
38 if (seq)
39 seq_vprintf(seq, fmt, args);
40 else
41 vprintk(fmt, args);
42 va_end(args);
43 }
44
45 /*
46 * Get the number of stack entries to skip to get out of MM internals. @type is
47 * optional, and if set to NULL, assumes an allocation or free stack.
48 */
get_stack_skipnr(const unsigned long stack_entries[],int num_entries,const enum kfence_error_type * type)49 static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries,
50 const enum kfence_error_type *type)
51 {
52 char buf[64];
53 int skipnr, fallback = 0;
54
55 if (type) {
56 /* Depending on error type, find different stack entries. */
57 switch (*type) {
58 case KFENCE_ERROR_UAF:
59 case KFENCE_ERROR_OOB:
60 case KFENCE_ERROR_INVALID:
61 /*
62 * kfence_handle_page_fault() may be called with pt_regs
63 * set to NULL; in that case we'll simply show the full
64 * stack trace.
65 */
66 return 0;
67 case KFENCE_ERROR_CORRUPTION:
68 case KFENCE_ERROR_INVALID_FREE:
69 break;
70 }
71 }
72
73 for (skipnr = 0; skipnr < num_entries; skipnr++) {
74 int len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skipnr]);
75
76 if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfence_") ||
77 str_has_prefix(buf, ARCH_FUNC_PREFIX "__kfence_") ||
78 !strncmp(buf, ARCH_FUNC_PREFIX "__slab_free", len)) {
79 /*
80 * In case of tail calls from any of the below
81 * to any of the above.
82 */
83 fallback = skipnr + 1;
84 }
85
86 /* Also the *_bulk() variants by only checking prefixes. */
87 if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfree") ||
88 str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_free") ||
89 str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmalloc") ||
90 str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_alloc"))
91 goto found;
92 }
93 if (fallback < num_entries)
94 return fallback;
95 found:
96 skipnr++;
97 return skipnr < num_entries ? skipnr : 0;
98 }
99
kfence_print_stack(struct seq_file * seq,const struct kfence_metadata * meta,bool show_alloc)100 static void kfence_print_stack(struct seq_file *seq, const struct kfence_metadata *meta,
101 bool show_alloc)
102 {
103 const struct kfence_track *track = show_alloc ? &meta->alloc_track : &meta->free_track;
104 u64 ts_sec = track->ts_nsec;
105 unsigned long rem_nsec = do_div(ts_sec, NSEC_PER_SEC);
106
107 /* Timestamp matches printk timestamp format. */
108 seq_con_printf(seq, "%s by task %d on cpu %d at %lu.%06lus:\n",
109 show_alloc ? "allocated" : "freed", track->pid,
110 track->cpu, (unsigned long)ts_sec, rem_nsec / 1000);
111
112 if (track->num_stack_entries) {
113 /* Skip allocation/free internals stack. */
114 int i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL);
115
116 /* stack_trace_seq_print() does not exist; open code our own. */
117 for (; i < track->num_stack_entries; i++)
118 seq_con_printf(seq, " %pS\n", (void *)track->stack_entries[i]);
119 } else {
120 seq_con_printf(seq, " no %s stack\n", show_alloc ? "allocation" : "deallocation");
121 }
122 }
123
kfence_print_object(struct seq_file * seq,const struct kfence_metadata * meta)124 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta)
125 {
126 const int size = abs(meta->size);
127 const unsigned long start = meta->addr;
128 const struct kmem_cache *const cache = meta->cache;
129
130 lockdep_assert_held(&meta->lock);
131
132 if (meta->state == KFENCE_OBJECT_UNUSED) {
133 seq_con_printf(seq, "kfence-#%td unused\n", meta - kfence_metadata);
134 return;
135 }
136
137 seq_con_printf(seq, "kfence-#%td: 0x%p-0x%p, size=%d, cache=%s\n\n",
138 meta - kfence_metadata, (void *)start, (void *)(start + size - 1),
139 size, (cache && cache->name) ? cache->name : "<destroyed>");
140
141 kfence_print_stack(seq, meta, true);
142
143 if (meta->state == KFENCE_OBJECT_FREED) {
144 seq_con_printf(seq, "\n");
145 kfence_print_stack(seq, meta, false);
146 }
147 }
148
149 /*
150 * Show bytes at @addr that are different from the expected canary values, up to
151 * @max_bytes.
152 */
print_diff_canary(unsigned long address,size_t bytes_to_show,const struct kfence_metadata * meta)153 static void print_diff_canary(unsigned long address, size_t bytes_to_show,
154 const struct kfence_metadata *meta)
155 {
156 const unsigned long show_until_addr = address + bytes_to_show;
157 const u8 *cur, *end;
158
159 /* Do not show contents of object nor read into following guard page. */
160 end = (const u8 *)(address < meta->addr ? min(show_until_addr, meta->addr)
161 : min(show_until_addr, PAGE_ALIGN(address)));
162
163 pr_cont("[");
164 for (cur = (const u8 *)address; cur < end; cur++) {
165 if (*cur == KFENCE_CANARY_PATTERN(cur))
166 pr_cont(" .");
167 else if (no_hash_pointers)
168 pr_cont(" 0x%02x", *cur);
169 else /* Do not leak kernel memory in non-debug builds. */
170 pr_cont(" !");
171 }
172 pr_cont(" ]");
173 }
174
get_access_type(bool is_write)175 static const char *get_access_type(bool is_write)
176 {
177 return is_write ? "write" : "read";
178 }
179
kfence_report_error(unsigned long address,bool is_write,struct pt_regs * regs,const struct kfence_metadata * meta,enum kfence_error_type type)180 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
181 const struct kfence_metadata *meta, enum kfence_error_type type)
182 {
183 unsigned long stack_entries[KFENCE_STACK_DEPTH] = { 0 };
184 const ptrdiff_t object_index = meta ? meta - kfence_metadata : -1;
185 int num_stack_entries;
186 int skipnr = 0;
187
188 if (regs) {
189 num_stack_entries = stack_trace_save_regs(regs, stack_entries, KFENCE_STACK_DEPTH, 0);
190 } else {
191 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 1);
192 skipnr = get_stack_skipnr(stack_entries, num_stack_entries, &type);
193 }
194
195 /* Require non-NULL meta, except if KFENCE_ERROR_INVALID. */
196 if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta))
197 return;
198
199 if (meta)
200 lockdep_assert_held(&meta->lock);
201 /*
202 * Because we may generate reports in printk-unfriendly parts of the
203 * kernel, such as scheduler code, the use of printk() could deadlock.
204 * Until such time that all printing code here is safe in all parts of
205 * the kernel, accept the risk, and just get our message out (given the
206 * system might already behave unpredictably due to the memory error).
207 * As such, also disable lockdep to hide warnings, and avoid disabling
208 * lockdep for the rest of the kernel.
209 */
210 lockdep_off();
211
212 pr_err("==================================================================\n");
213 /* Print report header. */
214 switch (type) {
215 case KFENCE_ERROR_OOB: {
216 const bool left_of_object = address < meta->addr;
217
218 pr_err("BUG: KFENCE: out-of-bounds %s in %pS\n\n", get_access_type(is_write),
219 (void *)stack_entries[skipnr]);
220 pr_err("Out-of-bounds %s at 0x%p (%luB %s of kfence-#%td):\n",
221 get_access_type(is_write), (void *)address,
222 left_of_object ? meta->addr - address : address - meta->addr,
223 left_of_object ? "left" : "right", object_index);
224 break;
225 }
226 case KFENCE_ERROR_UAF:
227 pr_err("BUG: KFENCE: use-after-free %s in %pS\n\n", get_access_type(is_write),
228 (void *)stack_entries[skipnr]);
229 pr_err("Use-after-free %s at 0x%p (in kfence-#%td):\n",
230 get_access_type(is_write), (void *)address, object_index);
231 break;
232 case KFENCE_ERROR_CORRUPTION:
233 pr_err("BUG: KFENCE: memory corruption in %pS\n\n", (void *)stack_entries[skipnr]);
234 pr_err("Corrupted memory at 0x%p ", (void *)address);
235 print_diff_canary(address, 16, meta);
236 pr_cont(" (in kfence-#%td):\n", object_index);
237 break;
238 case KFENCE_ERROR_INVALID:
239 pr_err("BUG: KFENCE: invalid %s in %pS\n\n", get_access_type(is_write),
240 (void *)stack_entries[skipnr]);
241 pr_err("Invalid %s at 0x%p:\n", get_access_type(is_write),
242 (void *)address);
243 break;
244 case KFENCE_ERROR_INVALID_FREE:
245 pr_err("BUG: KFENCE: invalid free in %pS\n\n", (void *)stack_entries[skipnr]);
246 pr_err("Invalid free of 0x%p (in kfence-#%td):\n", (void *)address,
247 object_index);
248 break;
249 }
250
251 /* Print stack trace and object info. */
252 stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0);
253
254 if (meta) {
255 pr_err("\n");
256 kfence_print_object(NULL, meta);
257 }
258
259 /* Print report footer. */
260 pr_err("\n");
261 if (no_hash_pointers && regs)
262 show_regs(regs);
263 else
264 dump_stack_print_info(KERN_ERR);
265 trace_error_report_end(ERROR_DETECTOR_KFENCE, address);
266 pr_err("==================================================================\n");
267
268 lockdep_on();
269
270 if (panic_on_warn)
271 panic("panic_on_warn set ...\n");
272
273 /* We encountered a memory safety error, taint the kernel! */
274 add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK);
275 }
276