[patch 207/262] kfence: move saving stack trace of allocations into __kfence_alloc()

Andrew Morton
2021-11-05T20:45:34Z

From: Marco Elver <elver@google.com>
Subject: kfence: move saving stack trace of allocations into __kfence_alloc()

Move the saving of the stack trace of allocations into __kfence_alloc(),
so that the stack entries array can be used outside of
kfence_guarded_alloc() and we avoid potentially unwinding the stack
multiple times.

Link: https://lkml.kernel.org/r/20210923104803.2620285-3-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Alexander Potapenko <glider@google.com>
Cc: Aleksandr Nogikh <nogikh@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Taras Madan <tarasmadan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/kfence/core.c | 35 ++++++++++++++++++++++++-----------
1 file changed, 24 insertions(+), 11 deletions(-)

--- a/mm/kfence/core.c~kfence-move-saving-stack-trace-of-allocations-into-__kfence_alloc
+++ a/mm/kfence/core.c
@@ -187,19 +187,26 @@ static inline unsigned long metadata_to_
* Update the object's metadata state, including updating the alloc/free stacks
* depending on the state transition.
*/
-static noinline void metadata_update_state(struct kfence_metadata *meta,
- enum kfence_object_state next)
+static noinline void
+metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state next,
+ unsigned long *stack_entries, size_t num_stack_entries)
{
struct kfence_track *track =
next == KFENCE_OBJECT_FREED ? &meta->free_track : &meta->alloc_track;

lockdep_assert_held(&meta->lock);

- /*
- * Skip over 1 (this) functions; noinline ensures we do not accidentally
- * skip over the caller by never inlining.
- */
- track->num_stack_entries = stack_trace_save(track->stack_entries, KFENCE_STACK_DEPTH, 1);
+ if (stack_entries) {
+ memcpy(track->stack_entries, stack_entries,
+ num_stack_entries * sizeof(stack_entries[0]));
+ } else {
+ /*
+ * Skip over 1 (this) functions; noinline ensures we do not
+ * accidentally skip over the caller by never inlining.
+ */
+ num_stack_entries = stack_trace_save(track->stack_entries, KFENCE_STACK_DEPTH, 1);
+ }
+ track->num_stack_entries = num_stack_entries;
track->pid = task_pid_nr(current);
track->cpu = raw_smp_processor_id();
track->ts_nsec = local_clock(); /* Same source as printk timestamps. */
@@ -261,7 +268,8 @@ static __always_inline void for_each_can
}
}

-static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t gfp)
+static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t gfp,
+ unsigned long *stack_entries, size_t num_stack_entries)
{
struct kfence_metadata *meta = NULL;
unsigned long flags;
@@ -320,7 +328,7 @@ static void *kfence_guarded_alloc(struct
addr = (void *)meta->addr;

/* Update remaining metadata. */
- metadata_update_state(meta, KFENCE_OBJECT_ALLOCATED);
+ metadata_update_state(meta, KFENCE_OBJECT_ALLOCATED, stack_entries, num_stack_entries);
/* Pairs with READ_ONCE() in kfence_shutdown_cache(). */
WRITE_ONCE(meta->cache, cache);
meta->size = size;
@@ -400,7 +408,7 @@ static void kfence_guarded_free(void *ad
memzero_explicit(addr, meta->size);

/* Mark the object as freed. */
- metadata_update_state(meta, KFENCE_OBJECT_FREED);
+ metadata_update_state(meta, KFENCE_OBJECT_FREED, NULL, 0);

raw_spin_unlock_irqrestore(&meta->lock, flags);

@@ -742,6 +750,9 @@ void kfence_shutdown_cache(struct kmem_c

void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
{
+ unsigned long stack_entries[KFENCE_STACK_DEPTH];
+ size_t num_stack_entries;
+
/*
* Perform size check before switching kfence_allocation_gate, so that
* we don't disable KFENCE without making an allocation.
@@ -786,7 +797,9 @@ void *__kfence_alloc(struct kmem_cache *
if (!READ_ONCE(kfence_enabled))
return NULL;

- return kfence_guarded_alloc(s, size, flags);
+ num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 0);
+
+ return kfence_guarded_alloc(s, size, flags, stack_entries, num_stack_entries);
}

size_t kfence_ksize(const void *addr)
_