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// 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);
}
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