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