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kfence: show cpu and timestamp in alloc/free info
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Record cpu and timestamp on allocations and frees, and show them in
reports.  Upon an error, this can help correlate earlier messages in the
kernel log via allocation and free timestamps.

Link: https://lkml.kernel.org/r/20210714175312.2947941-1-elver@google.com
Suggested-by: Joern Engel <joern@purestorage.com>
Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Alexander Potapenko <glider@google.com>
Acked-by: Joern Engel <joern@purestorage.com>
Cc: Yuanyuan Zhong <yzhong@purestorage.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Marco Elver authored and Linus Torvalds committed Sep 8, 2021
1 parent 1108605 commit 4bbf04a
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98 changes: 53 additions & 45 deletions Documentation/dev-tools/kfence.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -65,25 +65,27 @@ Error reports
A typical out-of-bounds access looks like this::

==================================================================
BUG: KFENCE: out-of-bounds read in test_out_of_bounds_read+0xa3/0x22b
BUG: KFENCE: out-of-bounds read in test_out_of_bounds_read+0xa6/0x234

Out-of-bounds read at 0xffffffffb672efff (1B left of kfence-#17):
test_out_of_bounds_read+0xa3/0x22b
kunit_try_run_case+0x51/0x85
Out-of-bounds read at 0xffff8c3f2e291fff (1B left of kfence-#72):
test_out_of_bounds_read+0xa6/0x234
kunit_try_run_case+0x61/0xa0
kunit_generic_run_threadfn_adapter+0x16/0x30
kthread+0x137/0x160
kthread+0x176/0x1b0
ret_from_fork+0x22/0x30

kfence-#17 [0xffffffffb672f000-0xffffffffb672f01f, size=32, cache=kmalloc-32] allocated by task 507:
test_alloc+0xf3/0x25b
test_out_of_bounds_read+0x98/0x22b
kunit_try_run_case+0x51/0x85
kfence-#72: 0xffff8c3f2e292000-0xffff8c3f2e29201f, size=32, cache=kmalloc-32

allocated by task 484 on cpu 0 at 32.919330s:
test_alloc+0xfe/0x738
test_out_of_bounds_read+0x9b/0x234
kunit_try_run_case+0x61/0xa0
kunit_generic_run_threadfn_adapter+0x16/0x30
kthread+0x137/0x160
kthread+0x176/0x1b0
ret_from_fork+0x22/0x30

CPU: 4 PID: 107 Comm: kunit_try_catch Not tainted 5.8.0-rc6+ #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
CPU: 0 PID: 484 Comm: kunit_try_catch Not tainted 5.13.0-rc3+ #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
==================================================================

The header of the report provides a short summary of the function involved in
Expand All @@ -96,61 +98,65 @@ Use-after-free accesses are reported as::
==================================================================
BUG: KFENCE: use-after-free read in test_use_after_free_read+0xb3/0x143

Use-after-free read at 0xffffffffb673dfe0 (in kfence-#24):
Use-after-free read at 0xffff8c3f2e2a0000 (in kfence-#79):
test_use_after_free_read+0xb3/0x143
kunit_try_run_case+0x51/0x85
kunit_try_run_case+0x61/0xa0
kunit_generic_run_threadfn_adapter+0x16/0x30
kthread+0x137/0x160
kthread+0x176/0x1b0
ret_from_fork+0x22/0x30

kfence-#24 [0xffffffffb673dfe0-0xffffffffb673dfff, size=32, cache=kmalloc-32] allocated by task 507:
test_alloc+0xf3/0x25b
kfence-#79: 0xffff8c3f2e2a0000-0xffff8c3f2e2a001f, size=32, cache=kmalloc-32

allocated by task 488 on cpu 2 at 33.871326s:
test_alloc+0xfe/0x738
test_use_after_free_read+0x76/0x143
kunit_try_run_case+0x51/0x85
kunit_try_run_case+0x61/0xa0
kunit_generic_run_threadfn_adapter+0x16/0x30
kthread+0x137/0x160
kthread+0x176/0x1b0
ret_from_fork+0x22/0x30

freed by task 507:
freed by task 488 on cpu 2 at 33.871358s:
test_use_after_free_read+0xa8/0x143
kunit_try_run_case+0x51/0x85
kunit_try_run_case+0x61/0xa0
kunit_generic_run_threadfn_adapter+0x16/0x30
kthread+0x137/0x160
kthread+0x176/0x1b0
ret_from_fork+0x22/0x30

CPU: 4 PID: 109 Comm: kunit_try_catch Tainted: G W 5.8.0-rc6+ #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
CPU: 2 PID: 488 Comm: kunit_try_catch Tainted: G B 5.13.0-rc3+ #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
==================================================================

KFENCE also reports on invalid frees, such as double-frees::

==================================================================
BUG: KFENCE: invalid free in test_double_free+0xdc/0x171

Invalid free of 0xffffffffb6741000:
Invalid free of 0xffff8c3f2e2a4000 (in kfence-#81):
test_double_free+0xdc/0x171
kunit_try_run_case+0x51/0x85
kunit_try_run_case+0x61/0xa0
kunit_generic_run_threadfn_adapter+0x16/0x30
kthread+0x137/0x160
kthread+0x176/0x1b0
ret_from_fork+0x22/0x30

kfence-#26 [0xffffffffb6741000-0xffffffffb674101f, size=32, cache=kmalloc-32] allocated by task 507:
test_alloc+0xf3/0x25b
kfence-#81: 0xffff8c3f2e2a4000-0xffff8c3f2e2a401f, size=32, cache=kmalloc-32

allocated by task 490 on cpu 1 at 34.175321s:
test_alloc+0xfe/0x738
test_double_free+0x76/0x171
kunit_try_run_case+0x51/0x85
kunit_try_run_case+0x61/0xa0
kunit_generic_run_threadfn_adapter+0x16/0x30
kthread+0x137/0x160
kthread+0x176/0x1b0
ret_from_fork+0x22/0x30

freed by task 507:
freed by task 490 on cpu 1 at 34.175348s:
test_double_free+0xa8/0x171
kunit_try_run_case+0x51/0x85
kunit_try_run_case+0x61/0xa0
kunit_generic_run_threadfn_adapter+0x16/0x30
kthread+0x137/0x160
kthread+0x176/0x1b0
ret_from_fork+0x22/0x30

CPU: 4 PID: 111 Comm: kunit_try_catch Tainted: G W 5.8.0-rc6+ #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
CPU: 1 PID: 490 Comm: kunit_try_catch Tainted: G B 5.13.0-rc3+ #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
==================================================================

KFENCE also uses pattern-based redzones on the other side of an object's guard
Expand All @@ -160,23 +166,25 @@ These are reported on frees::
==================================================================
BUG: KFENCE: memory corruption in test_kmalloc_aligned_oob_write+0xef/0x184

Corrupted memory at 0xffffffffb6797ff9 [ 0xac . . . . . . ] (in kfence-#69):
Corrupted memory at 0xffff8c3f2e33aff9 [ 0xac . . . . . . ] (in kfence-#156):
test_kmalloc_aligned_oob_write+0xef/0x184
kunit_try_run_case+0x51/0x85
kunit_try_run_case+0x61/0xa0
kunit_generic_run_threadfn_adapter+0x16/0x30
kthread+0x137/0x160
kthread+0x176/0x1b0
ret_from_fork+0x22/0x30

kfence-#69 [0xffffffffb6797fb0-0xffffffffb6797ff8, size=73, cache=kmalloc-96] allocated by task 507:
test_alloc+0xf3/0x25b
kfence-#156: 0xffff8c3f2e33afb0-0xffff8c3f2e33aff8, size=73, cache=kmalloc-96

allocated by task 502 on cpu 7 at 42.159302s:
test_alloc+0xfe/0x738
test_kmalloc_aligned_oob_write+0x57/0x184
kunit_try_run_case+0x51/0x85
kunit_try_run_case+0x61/0xa0
kunit_generic_run_threadfn_adapter+0x16/0x30
kthread+0x137/0x160
kthread+0x176/0x1b0
ret_from_fork+0x22/0x30

CPU: 4 PID: 120 Comm: kunit_try_catch Tainted: G W 5.8.0-rc6+ #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
CPU: 7 PID: 502 Comm: kunit_try_catch Tainted: G B 5.13.0-rc3+ #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
==================================================================

For such errors, the address where the corruption occurred as well as the
Expand Down
3 changes: 3 additions & 0 deletions mm/kfence/core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
#include <linux/moduleparam.h>
#include <linux/random.h>
#include <linux/rcupdate.h>
#include <linux/sched/clock.h>
#include <linux/sched/sysctl.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
Expand Down Expand Up @@ -196,6 +197,8 @@ static noinline void metadata_update_state(struct kfence_metadata *meta,
*/
track->num_stack_entries = stack_trace_save(track->stack_entries, KFENCE_STACK_DEPTH, 1);
track->pid = task_pid_nr(current);
track->cpu = raw_smp_processor_id();
track->ts_nsec = local_clock(); /* Same source as printk timestamps. */

/*
* Pairs with READ_ONCE() in
Expand Down
2 changes: 2 additions & 0 deletions mm/kfence/kfence.h
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,8 @@ enum kfence_object_state {
/* Alloc/free tracking information. */
struct kfence_track {
pid_t pid;
int cpu;
u64 ts_nsec;
int num_stack_entries;
unsigned long stack_entries[KFENCE_STACK_DEPTH];
};
Expand Down
19 changes: 13 additions & 6 deletions mm/kfence/report.c
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@

#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>
Expand Down Expand Up @@ -100,6 +101,13 @@ static void kfence_print_stack(struct seq_file *seq, const struct kfence_metadat
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. */
Expand All @@ -126,15 +134,14 @@ void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *met
return;
}

seq_con_printf(seq,
"kfence-#%td [0x%p-0x%p"
", 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);
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, "\nfreed by task %d:\n", meta->free_track.pid);
seq_con_printf(seq, "\n");
kfence_print_stack(seq, meta, false);
}
}
Expand Down

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