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/sprintf.h> 17 #include <linux/stacktrace.h> 18 #include <linux/string.h> 19 #include <linux/sched/clock.h> 20 #include <trace/events/error_report.h> 21 22 #include <asm/kfence.h> 23 24 #include "kfence.h" 25 26 /* May be overridden by <asm/kfence.h>. */ 27 #ifndef ARCH_FUNC_PREFIX 28 #define ARCH_FUNC_PREFIX "" 29 #endif 30 31 /* Helper function to either print to a seq_file or to console. */ 32 __printf(2, 3) 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 */ 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 str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmem_cache_free") || 79 !strncmp(buf, ARCH_FUNC_PREFIX "__slab_free", len)) { 80 /* 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. 84 */ 85 fallback = skipnr + 1; 86 } 87 88 /* 89 * The below list should only include the initial entry points 90 * into the slab allocators. Includes the *_bulk() variants by 91 * checking prefixes. 92 */ 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")) 97 goto found; 98 } 99 if (fallback < num_entries) 100 return fallback; 101 found: 102 skipnr++; 103 return skipnr < num_entries ? skipnr : 0; 104 } 105 106 static void kfence_print_stack(struct seq_file *seq, const struct kfence_metadata *meta, 107 bool show_alloc) 108 { 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); 112 u64 interval_nsec = local_clock() - track->ts_nsec; 113 unsigned long rem_interval_nsec = do_div(interval_nsec, NSEC_PER_SEC); 114 115 /* Timestamp matches printk timestamp format. */ 116 seq_con_printf(seq, "%s by task %d on cpu %d at %lu.%06lus (%lu.%06lus ago):\n", 117 show_alloc ? "allocated" : meta->state == KFENCE_OBJECT_RCU_FREEING ? 118 "rcu freeing" : "freed", track->pid, 119 track->cpu, (unsigned long)ts_sec, rem_nsec / 1000, 120 (unsigned long)interval_nsec, rem_interval_nsec / 1000); 121 122 if (track->num_stack_entries) { 123 /* Skip allocation/free internals stack. */ 124 int i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL); 125 126 /* stack_trace_seq_print() does not exist; open code our own. */ 127 for (; i < track->num_stack_entries; i++) 128 seq_con_printf(seq, " %pS\n", (void *)track->stack_entries[i]); 129 } else { 130 seq_con_printf(seq, " no %s stack\n", show_alloc ? "allocation" : "deallocation"); 131 } 132 } 133 134 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta) 135 { 136 const int size = abs(meta->size); 137 const unsigned long start = meta->addr; 138 const struct kmem_cache *const cache = meta->cache; 139 140 lockdep_assert_held(&meta->lock); 141 142 if (meta->state == KFENCE_OBJECT_UNUSED) { 143 seq_con_printf(seq, "kfence-#%td unused\n", meta - kfence_metadata); 144 return; 145 } 146 147 seq_con_printf(seq, "kfence-#%td: 0x%p-0x%p, size=%d, cache=%s\n\n", 148 meta - kfence_metadata, (void *)start, (void *)(start + size - 1), 149 size, (cache && cache->name) ? cache->name : "<destroyed>"); 150 151 kfence_print_stack(seq, meta, true); 152 153 if (meta->state == KFENCE_OBJECT_FREED || meta->state == KFENCE_OBJECT_RCU_FREEING) { 154 seq_con_printf(seq, "\n"); 155 kfence_print_stack(seq, meta, false); 156 } 157 } 158 159 /* 160 * Show bytes at @addr that are different from the expected canary values, up to 161 * @max_bytes. 162 */ 163 static void print_diff_canary(unsigned long address, size_t bytes_to_show, 164 const struct kfence_metadata *meta) 165 { 166 const unsigned long show_until_addr = address + bytes_to_show; 167 const u8 *cur, *end; 168 169 /* Do not show contents of object nor read into following guard page. */ 170 end = (const u8 *)(address < meta->addr ? min(show_until_addr, meta->addr) 171 : min(show_until_addr, PAGE_ALIGN(address))); 172 173 pr_cont("["); 174 for (cur = (const u8 *)address; cur < end; cur++) { 175 if (*cur == KFENCE_CANARY_PATTERN_U8(cur)) 176 pr_cont(" ."); 177 else if (no_hash_pointers) 178 pr_cont(" 0x%02x", *cur); 179 else /* Do not leak kernel memory in non-debug builds. */ 180 pr_cont(" !"); 181 } 182 pr_cont(" ]"); 183 } 184 185 static const char *get_access_type(bool is_write) 186 { 187 return is_write ? "write" : "read"; 188 } 189 190 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs, 191 const struct kfence_metadata *meta, enum kfence_error_type type) 192 { 193 unsigned long stack_entries[KFENCE_STACK_DEPTH] = { 0 }; 194 const ptrdiff_t object_index = meta ? meta - kfence_metadata : -1; 195 int num_stack_entries; 196 int skipnr = 0; 197 198 if (regs) { 199 num_stack_entries = stack_trace_save_regs(regs, stack_entries, KFENCE_STACK_DEPTH, 0); 200 } else { 201 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 1); 202 skipnr = get_stack_skipnr(stack_entries, num_stack_entries, &type); 203 } 204 205 /* Require non-NULL meta, except if KFENCE_ERROR_INVALID. */ 206 if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta)) 207 return; 208 209 if (meta) 210 lockdep_assert_held(&meta->lock); 211 /* 212 * Because we may generate reports in printk-unfriendly parts of the 213 * kernel, such as scheduler code, the use of printk() could deadlock. 214 * Until such time that all printing code here is safe in all parts of 215 * the kernel, accept the risk, and just get our message out (given the 216 * system might already behave unpredictably due to the memory error). 217 * As such, also disable lockdep to hide warnings, and avoid disabling 218 * lockdep for the rest of the kernel. 219 */ 220 lockdep_off(); 221 222 pr_err("==================================================================\n"); 223 /* Print report header. */ 224 switch (type) { 225 case KFENCE_ERROR_OOB: { 226 const bool left_of_object = address < meta->addr; 227 228 pr_err("BUG: KFENCE: out-of-bounds %s in %pS\n\n", get_access_type(is_write), 229 (void *)stack_entries[skipnr]); 230 pr_err("Out-of-bounds %s at 0x%p (%luB %s of kfence-#%td):\n", 231 get_access_type(is_write), (void *)address, 232 left_of_object ? meta->addr - address : address - meta->addr, 233 left_of_object ? "left" : "right", object_index); 234 break; 235 } 236 case KFENCE_ERROR_UAF: 237 pr_err("BUG: KFENCE: use-after-free %s in %pS\n\n", get_access_type(is_write), 238 (void *)stack_entries[skipnr]); 239 pr_err("Use-after-free %s at 0x%p (in kfence-#%td):\n", 240 get_access_type(is_write), (void *)address, object_index); 241 break; 242 case KFENCE_ERROR_CORRUPTION: 243 pr_err("BUG: KFENCE: memory corruption in %pS\n\n", (void *)stack_entries[skipnr]); 244 pr_err("Corrupted memory at 0x%p ", (void *)address); 245 print_diff_canary(address, 16, meta); 246 pr_cont(" (in kfence-#%td):\n", object_index); 247 break; 248 case KFENCE_ERROR_INVALID: 249 pr_err("BUG: KFENCE: invalid %s in %pS\n\n", get_access_type(is_write), 250 (void *)stack_entries[skipnr]); 251 pr_err("Invalid %s at 0x%p:\n", get_access_type(is_write), 252 (void *)address); 253 break; 254 case KFENCE_ERROR_INVALID_FREE: 255 pr_err("BUG: KFENCE: invalid free in %pS\n\n", (void *)stack_entries[skipnr]); 256 pr_err("Invalid free of 0x%p (in kfence-#%td):\n", (void *)address, 257 object_index); 258 break; 259 } 260 261 /* Print stack trace and object info. */ 262 stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0); 263 264 if (meta) { 265 pr_err("\n"); 266 kfence_print_object(NULL, meta); 267 } 268 269 /* Print report footer. */ 270 pr_err("\n"); 271 if (no_hash_pointers && regs) 272 show_regs(regs); 273 else 274 dump_stack_print_info(KERN_ERR); 275 trace_error_report_end(ERROR_DETECTOR_KFENCE, address); 276 pr_err("==================================================================\n"); 277 278 lockdep_on(); 279 280 check_panic_on_warn("KFENCE"); 281 282 /* We encountered a memory safety error, taint the kernel! */ 283 add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK); 284 } 285 286 #ifdef CONFIG_PRINTK 287 static void kfence_to_kp_stack(const struct kfence_track *track, void **kp_stack) 288 { 289 int i, j; 290 291 i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL); 292 for (j = 0; i < track->num_stack_entries && j < KS_ADDRS_COUNT; ++i, ++j) 293 kp_stack[j] = (void *)track->stack_entries[i]; 294 if (j < KS_ADDRS_COUNT) 295 kp_stack[j] = NULL; 296 } 297 298 bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) 299 { 300 struct kfence_metadata *meta = addr_to_metadata((unsigned long)object); 301 unsigned long flags; 302 303 if (!meta) 304 return false; 305 306 /* 307 * If state is UNUSED at least show the pointer requested; the rest 308 * would be garbage data. 309 */ 310 kpp->kp_ptr = object; 311 312 /* Requesting info an a never-used object is almost certainly a bug. */ 313 if (WARN_ON(meta->state == KFENCE_OBJECT_UNUSED)) 314 return true; 315 316 raw_spin_lock_irqsave(&meta->lock, flags); 317 318 kpp->kp_slab = slab; 319 kpp->kp_slab_cache = meta->cache; 320 kpp->kp_objp = (void *)meta->addr; 321 kfence_to_kp_stack(&meta->alloc_track, kpp->kp_stack); 322 if (meta->state == KFENCE_OBJECT_FREED || meta->state == KFENCE_OBJECT_RCU_FREEING) 323 kfence_to_kp_stack(&meta->free_track, kpp->kp_free_stack); 324 /* get_stack_skipnr() ensures the first entry is outside allocator. */ 325 kpp->kp_ret = kpp->kp_stack[0]; 326 327 raw_spin_unlock_irqrestore(&meta->lock, flags); 328 329 return true; 330 } 331 #endif 332