1 // SPDX-License-Identifier: GPL-2.0
5 * Copyright (C) 2020, Google LLC.
8 #include <linux/stdarg.h>
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>
20 #include <asm/kfence.h>
24 /* May be overridden by <asm/kfence.h>. */
25 #ifndef ARCH_FUNC_PREFIX
26 #define ARCH_FUNC_PREFIX ""
29 extern bool no_hash_pointers;
31 /* Helper function to either print to a seq_file or to console. */
33 static void seq_con_printf(struct seq_file *seq, const char *fmt, ...)
39 seq_vprintf(seq, fmt, args);
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.
49 static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries,
50 const enum kfence_error_type *type)
53 int skipnr, fallback = 0;
56 /* Depending on error type, find different stack entries. */
58 case KFENCE_ERROR_UAF:
59 case KFENCE_ERROR_OOB:
60 case KFENCE_ERROR_INVALID:
62 * kfence_handle_page_fault() may be called with pt_regs
63 * set to NULL; in that case we'll simply show the full
67 case KFENCE_ERROR_CORRUPTION:
68 case KFENCE_ERROR_INVALID_FREE:
73 for (skipnr = 0; skipnr < num_entries; skipnr++) {
74 int len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skipnr]);
76 if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfence_") ||
77 str_has_prefix(buf, ARCH_FUNC_PREFIX "__kfence_") ||
78 str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmem_cache_free") ||
79 !strncmp(buf, ARCH_FUNC_PREFIX "__slab_free", len)) {
81 * In case of tail calls from any of the below to any of
82 * the above, optimized by the compiler such that the
83 * stack trace would omit the initial entry point below.
85 fallback = skipnr + 1;
89 * The below list should only include the initial entry points
90 * into the slab allocators. Includes the *_bulk() variants by
93 if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfree") ||
94 str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_free") ||
95 str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmalloc") ||
96 str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_alloc"))
99 if (fallback < num_entries)
103 return skipnr < num_entries ? skipnr : 0;
106 static void kfence_print_stack(struct seq_file *seq, const struct kfence_metadata *meta,
109 const struct kfence_track *track = show_alloc ? &meta->alloc_track : &meta->free_track;
110 u64 ts_sec = track->ts_nsec;
111 unsigned long rem_nsec = do_div(ts_sec, NSEC_PER_SEC);
113 /* Timestamp matches printk timestamp format. */
114 seq_con_printf(seq, "%s by task %d on cpu %d at %lu.%06lus:\n",
115 show_alloc ? "allocated" : "freed", track->pid,
116 track->cpu, (unsigned long)ts_sec, rem_nsec / 1000);
118 if (track->num_stack_entries) {
119 /* Skip allocation/free internals stack. */
120 int i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL);
122 /* stack_trace_seq_print() does not exist; open code our own. */
123 for (; i < track->num_stack_entries; i++)
124 seq_con_printf(seq, " %pS\n", (void *)track->stack_entries[i]);
126 seq_con_printf(seq, " no %s stack\n", show_alloc ? "allocation" : "deallocation");
130 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta)
132 const int size = abs(meta->size);
133 const unsigned long start = meta->addr;
134 const struct kmem_cache *const cache = meta->cache;
136 lockdep_assert_held(&meta->lock);
138 if (meta->state == KFENCE_OBJECT_UNUSED) {
139 seq_con_printf(seq, "kfence-#%td unused\n", meta - kfence_metadata);
143 seq_con_printf(seq, "kfence-#%td: 0x%p-0x%p, size=%d, cache=%s\n\n",
144 meta - kfence_metadata, (void *)start, (void *)(start + size - 1),
145 size, (cache && cache->name) ? cache->name : "<destroyed>");
147 kfence_print_stack(seq, meta, true);
149 if (meta->state == KFENCE_OBJECT_FREED) {
150 seq_con_printf(seq, "\n");
151 kfence_print_stack(seq, meta, false);
156 * Show bytes at @addr that are different from the expected canary values, up to
159 static void print_diff_canary(unsigned long address, size_t bytes_to_show,
160 const struct kfence_metadata *meta)
162 const unsigned long show_until_addr = address + bytes_to_show;
165 /* Do not show contents of object nor read into following guard page. */
166 end = (const u8 *)(address < meta->addr ? min(show_until_addr, meta->addr)
167 : min(show_until_addr, PAGE_ALIGN(address)));
170 for (cur = (const u8 *)address; cur < end; cur++) {
171 if (*cur == KFENCE_CANARY_PATTERN(cur))
173 else if (no_hash_pointers)
174 pr_cont(" 0x%02x", *cur);
175 else /* Do not leak kernel memory in non-debug builds. */
181 static const char *get_access_type(bool is_write)
183 return is_write ? "write" : "read";
186 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
187 const struct kfence_metadata *meta, enum kfence_error_type type)
189 unsigned long stack_entries[KFENCE_STACK_DEPTH] = { 0 };
190 const ptrdiff_t object_index = meta ? meta - kfence_metadata : -1;
191 int num_stack_entries;
195 num_stack_entries = stack_trace_save_regs(regs, stack_entries, KFENCE_STACK_DEPTH, 0);
197 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 1);
198 skipnr = get_stack_skipnr(stack_entries, num_stack_entries, &type);
201 /* Require non-NULL meta, except if KFENCE_ERROR_INVALID. */
202 if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta))
206 lockdep_assert_held(&meta->lock);
208 * Because we may generate reports in printk-unfriendly parts of the
209 * kernel, such as scheduler code, the use of printk() could deadlock.
210 * Until such time that all printing code here is safe in all parts of
211 * the kernel, accept the risk, and just get our message out (given the
212 * system might already behave unpredictably due to the memory error).
213 * As such, also disable lockdep to hide warnings, and avoid disabling
214 * lockdep for the rest of the kernel.
218 pr_err("==================================================================\n");
219 /* Print report header. */
221 case KFENCE_ERROR_OOB: {
222 const bool left_of_object = address < meta->addr;
224 pr_err("BUG: KFENCE: out-of-bounds %s in %pS\n\n", get_access_type(is_write),
225 (void *)stack_entries[skipnr]);
226 pr_err("Out-of-bounds %s at 0x%p (%luB %s of kfence-#%td):\n",
227 get_access_type(is_write), (void *)address,
228 left_of_object ? meta->addr - address : address - meta->addr,
229 left_of_object ? "left" : "right", object_index);
232 case KFENCE_ERROR_UAF:
233 pr_err("BUG: KFENCE: use-after-free %s in %pS\n\n", get_access_type(is_write),
234 (void *)stack_entries[skipnr]);
235 pr_err("Use-after-free %s at 0x%p (in kfence-#%td):\n",
236 get_access_type(is_write), (void *)address, object_index);
238 case KFENCE_ERROR_CORRUPTION:
239 pr_err("BUG: KFENCE: memory corruption in %pS\n\n", (void *)stack_entries[skipnr]);
240 pr_err("Corrupted memory at 0x%p ", (void *)address);
241 print_diff_canary(address, 16, meta);
242 pr_cont(" (in kfence-#%td):\n", object_index);
244 case KFENCE_ERROR_INVALID:
245 pr_err("BUG: KFENCE: invalid %s in %pS\n\n", get_access_type(is_write),
246 (void *)stack_entries[skipnr]);
247 pr_err("Invalid %s at 0x%p:\n", get_access_type(is_write),
250 case KFENCE_ERROR_INVALID_FREE:
251 pr_err("BUG: KFENCE: invalid free in %pS\n\n", (void *)stack_entries[skipnr]);
252 pr_err("Invalid free of 0x%p (in kfence-#%td):\n", (void *)address,
257 /* Print stack trace and object info. */
258 stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0);
262 kfence_print_object(NULL, meta);
265 /* Print report footer. */
267 if (no_hash_pointers && regs)
270 dump_stack_print_info(KERN_ERR);
271 trace_error_report_end(ERROR_DETECTOR_KFENCE, address);
272 pr_err("==================================================================\n");
276 check_panic_on_warn("KFENCE");
278 /* We encountered a memory safety error, taint the kernel! */
279 add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK);
283 static void kfence_to_kp_stack(const struct kfence_track *track, void **kp_stack)
287 i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL);
288 for (j = 0; i < track->num_stack_entries && j < KS_ADDRS_COUNT; ++i, ++j)
289 kp_stack[j] = (void *)track->stack_entries[i];
290 if (j < KS_ADDRS_COUNT)
294 bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab)
296 struct kfence_metadata *meta = addr_to_metadata((unsigned long)object);
303 * If state is UNUSED at least show the pointer requested; the rest
304 * would be garbage data.
306 kpp->kp_ptr = object;
308 /* Requesting info an a never-used object is almost certainly a bug. */
309 if (WARN_ON(meta->state == KFENCE_OBJECT_UNUSED))
312 raw_spin_lock_irqsave(&meta->lock, flags);
315 kpp->kp_slab_cache = meta->cache;
316 kpp->kp_objp = (void *)meta->addr;
317 kfence_to_kp_stack(&meta->alloc_track, kpp->kp_stack);
318 if (meta->state == KFENCE_OBJECT_FREED)
319 kfence_to_kp_stack(&meta->free_track, kpp->kp_free_stack);
320 /* get_stack_skipnr() ensures the first entry is outside allocator. */
321 kpp->kp_ret = kpp->kp_stack[0];
323 raw_spin_unlock_irqrestore(&meta->lock, flags);