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- // SPDX-License-Identifier: GPL-2.0
- /*
- * KFENCE reporting.
- *
- * Copyright (C) 2020, Google LLC.
- */
- #include <linux/stdarg.h>
- #include <linux/kernel.h>
- #include <linux/lockdep.h>
- #include <linux/math.h>
- #include <linux/printk.h>
- #include <linux/sched/debug.h>
- #include <linux/seq_file.h>
- #include <linux/stacktrace.h>
- #include <linux/string.h>
- #include <trace/events/error_report.h>
- #include <asm/kfence.h>
- #include "kfence.h"
- /* May be overridden by <asm/kfence.h>. */
- #ifndef ARCH_FUNC_PREFIX
- #define ARCH_FUNC_PREFIX ""
- #endif
- extern bool no_hash_pointers;
- /* 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;
- if (type) {
- /* Depending on error type, find different stack entries. */
- switch (*type) {
- case KFENCE_ERROR_UAF:
- case KFENCE_ERROR_OOB:
- case KFENCE_ERROR_INVALID:
- /*
- * kfence_handle_page_fault() may be called with pt_regs
- * set to NULL; in that case we'll simply show the full
- * stack trace.
- */
- return 0;
- 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 (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfence_") ||
- str_has_prefix(buf, ARCH_FUNC_PREFIX "__kfence_") ||
- str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmem_cache_free") ||
- !strncmp(buf, ARCH_FUNC_PREFIX "__slab_free", len)) {
- /*
- * In case of tail calls from any of the below to any of
- * the above, optimized by the compiler such that the
- * stack trace would omit the initial entry point below.
- */
- fallback = skipnr + 1;
- }
- /*
- * The below list should only include the initial entry points
- * into the slab allocators. Includes the *_bulk() variants by
- * checking prefixes.
- */
- if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfree") ||
- str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_free") ||
- str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmalloc") ||
- str_has_prefix(buf, ARCH_FUNC_PREFIX "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;
- u64 ts_sec = track->ts_nsec;
- unsigned long rem_nsec = do_div(ts_sec, NSEC_PER_SEC);
- /* Timestamp matches printk timestamp format. */
- seq_con_printf(seq, "%s by task %d on cpu %d at %lu.%06lus:\n",
- show_alloc ? "allocated" : "freed", track->pid,
- track->cpu, (unsigned long)ts_sec, rem_nsec / 1000);
- 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-#%td unused\n", meta - kfence_metadata);
- return;
- }
- seq_con_printf(seq, "kfence-#%td: 0x%p-0x%p, size=%d, cache=%s\n\n",
- meta - kfence_metadata, (void *)start, (void *)(start + size - 1),
- size, (cache && cache->name) ? cache->name : "<destroyed>");
- kfence_print_stack(seq, meta, true);
- if (meta->state == KFENCE_OBJECT_FREED) {
- seq_con_printf(seq, "\n");
- 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 (no_hash_pointers)
- pr_cont(" 0x%02x", *cur);
- else /* Do not leak kernel memory in non-debug builds. */
- pr_cont(" !");
- }
- pr_cont(" ]");
- }
- static const char *get_access_type(bool is_write)
- {
- return is_write ? "write" : "read";
- }
- void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
- const struct kfence_metadata *meta, enum kfence_error_type type)
- {
- unsigned long stack_entries[KFENCE_STACK_DEPTH] = { 0 };
- const ptrdiff_t object_index = meta ? meta - kfence_metadata : -1;
- int num_stack_entries;
- int skipnr = 0;
- if (regs) {
- num_stack_entries = stack_trace_save_regs(regs, stack_entries, KFENCE_STACK_DEPTH, 0);
- } else {
- num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 1);
- skipnr = get_stack_skipnr(stack_entries, num_stack_entries, &type);
- }
- /* 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 %s in %pS\n\n", get_access_type(is_write),
- (void *)stack_entries[skipnr]);
- pr_err("Out-of-bounds %s at 0x%p (%luB %s of kfence-#%td):\n",
- get_access_type(is_write), (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 %s in %pS\n\n", get_access_type(is_write),
- (void *)stack_entries[skipnr]);
- pr_err("Use-after-free %s at 0x%p (in kfence-#%td):\n",
- get_access_type(is_write), (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%p ", (void *)address);
- print_diff_canary(address, 16, meta);
- pr_cont(" (in kfence-#%td):\n", object_index);
- break;
- case KFENCE_ERROR_INVALID:
- pr_err("BUG: KFENCE: invalid %s in %pS\n\n", get_access_type(is_write),
- (void *)stack_entries[skipnr]);
- pr_err("Invalid %s at 0x%p:\n", get_access_type(is_write),
- (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%p (in kfence-#%td):\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");
- if (no_hash_pointers && regs)
- show_regs(regs);
- else
- dump_stack_print_info(KERN_ERR);
- trace_error_report_end(ERROR_DETECTOR_KFENCE, address);
- pr_err("==================================================================\n");
- lockdep_on();
- check_panic_on_warn("KFENCE");
- /* We encountered a memory safety error, taint the kernel! */
- add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK);
- }
- #ifdef CONFIG_PRINTK
- static void kfence_to_kp_stack(const struct kfence_track *track, void **kp_stack)
- {
- int i, j;
- i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL);
- for (j = 0; i < track->num_stack_entries && j < KS_ADDRS_COUNT; ++i, ++j)
- kp_stack[j] = (void *)track->stack_entries[i];
- if (j < KS_ADDRS_COUNT)
- kp_stack[j] = NULL;
- }
- bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab)
- {
- struct kfence_metadata *meta = addr_to_metadata((unsigned long)object);
- unsigned long flags;
- if (!meta)
- return false;
- /*
- * If state is UNUSED at least show the pointer requested; the rest
- * would be garbage data.
- */
- kpp->kp_ptr = object;
- /* Requesting info an a never-used object is almost certainly a bug. */
- if (WARN_ON(meta->state == KFENCE_OBJECT_UNUSED))
- return true;
- raw_spin_lock_irqsave(&meta->lock, flags);
- kpp->kp_slab = slab;
- kpp->kp_slab_cache = meta->cache;
- kpp->kp_objp = (void *)meta->addr;
- kfence_to_kp_stack(&meta->alloc_track, kpp->kp_stack);
- if (meta->state == KFENCE_OBJECT_FREED)
- kfence_to_kp_stack(&meta->free_track, kpp->kp_free_stack);
- /* get_stack_skipnr() ensures the first entry is outside allocator. */
- kpp->kp_ret = kpp->kp_stack[0];
- raw_spin_unlock_irqrestore(&meta->lock, flags);
- return true;
- }
- #endif
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