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) 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); 112 113 /* 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); 117 118 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); 121 122 /* 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]); 125 } else { 126 seq_con_printf(seq, " no %s stack\n", show_alloc ? "allocation" : "deallocation"); 127 } 128 } 129 130 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta) 131 { 132 const int size = abs(meta->size); 133 const unsigned long start = meta->addr; 134 const struct kmem_cache *const cache = meta->cache; 135 136 lockdep_assert_held(&meta->lock); 137 138 if (meta->state == KFENCE_OBJECT_UNUSED) { 139 seq_con_printf(seq, "kfence-#%td unused\n", meta - kfence_metadata); 140 return; 141 } 142 143 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>"); 146 147 kfence_print_stack(seq, meta, true); 148 149 if (meta->state == KFENCE_OBJECT_FREED) { 150 seq_con_printf(seq, "\n"); 151 kfence_print_stack(seq, meta, false); 152 } 153 } 154 155 /* 156 * Show bytes at @addr that are different from the expected canary values, up to 157 * @max_bytes. 158 */ 159 static void print_diff_canary(unsigned long address, size_t bytes_to_show, 160 const struct kfence_metadata *meta) 161 { 162 const unsigned long show_until_addr = address + bytes_to_show; 163 const u8 *cur, *end; 164 165 /* 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))); 168 169 pr_cont("["); 170 for (cur = (const u8 *)address; cur < end; cur++) { 171 if (*cur == KFENCE_CANARY_PATTERN_U8(cur)) 172 pr_cont(" ."); 173 else if (no_hash_pointers) 174 pr_cont(" 0x%02x", *cur); 175 else /* Do not leak kernel memory in non-debug builds. */ 176 pr_cont(" !"); 177 } 178 pr_cont(" ]"); 179 } 180 181 static const char *get_access_type(bool is_write) 182 { 183 return is_write ? "write" : "read"; 184 } 185 186 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) 188 { 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; 192 int skipnr = 0; 193 194 if (regs) { 195 num_stack_entries = stack_trace_save_regs(regs, stack_entries, KFENCE_STACK_DEPTH, 0); 196 } else { 197 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 1); 198 skipnr = get_stack_skipnr(stack_entries, num_stack_entries, &type); 199 } 200 201 /* Require non-NULL meta, except if KFENCE_ERROR_INVALID. */ 202 if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta)) 203 return; 204 205 if (meta) 206 lockdep_assert_held(&meta->lock); 207 /* 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. 215 */ 216 lockdep_off(); 217 218 pr_err("==================================================================\n"); 219 /* Print report header. */ 220 switch (type) { 221 case KFENCE_ERROR_OOB: { 222 const bool left_of_object = address < meta->addr; 223 224 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); 230 break; 231 } 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); 237 break; 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); 243 break; 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), 248 (void *)address); 249 break; 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, 253 object_index); 254 break; 255 } 256 257 /* Print stack trace and object info. */ 258 stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0); 259 260 if (meta) { 261 pr_err("\n"); 262 kfence_print_object(NULL, meta); 263 } 264 265 /* Print report footer. */ 266 pr_err("\n"); 267 if (no_hash_pointers && regs) 268 show_regs(regs); 269 else 270 dump_stack_print_info(KERN_ERR); 271 trace_error_report_end(ERROR_DETECTOR_KFENCE, address); 272 pr_err("==================================================================\n"); 273 274 lockdep_on(); 275 276 check_panic_on_warn("KFENCE"); 277 278 /* We encountered a memory safety error, taint the kernel! */ 279 add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK); 280 } 281 282 #ifdef CONFIG_PRINTK 283 static void kfence_to_kp_stack(const struct kfence_track *track, void **kp_stack) 284 { 285 int i, j; 286 287 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) 291 kp_stack[j] = NULL; 292 } 293 294 bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) 295 { 296 struct kfence_metadata *meta = addr_to_metadata((unsigned long)object); 297 unsigned long flags; 298 299 if (!meta) 300 return false; 301 302 /* 303 * If state is UNUSED at least show the pointer requested; the rest 304 * would be garbage data. 305 */ 306 kpp->kp_ptr = object; 307 308 /* Requesting info an a never-used object is almost certainly a bug. */ 309 if (WARN_ON(meta->state == KFENCE_OBJECT_UNUSED)) 310 return true; 311 312 raw_spin_lock_irqsave(&meta->lock, flags); 313 314 kpp->kp_slab = slab; 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]; 322 323 raw_spin_unlock_irqrestore(&meta->lock, flags); 324 325 return true; 326 } 327 #endif 328