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Subject[PATCH 5.13 196/223] kfence: move the size check to the beginning of __kfence_alloc()
Date
From: Alexander Potapenko <glider@google.com>

commit 235a85cb32bb123854ad31de46fdbf04c1d57cda upstream.

Check the allocation size before toggling kfence_allocation_gate.

This way allocations that can't be served by KFENCE will not result in
waiting for another CONFIG_KFENCE_SAMPLE_INTERVAL without allocating
anything.

Link: https://lkml.kernel.org/r/20210714092222.1890268-1-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Suggested-by: Marco Elver <elver@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: <stable@vger.kernel.org> [5.12+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/kfence/core.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -734,6 +734,13 @@ void kfence_shutdown_cache(struct kmem_c
void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
{
/*
+ * Perform size check before switching kfence_allocation_gate, so that
+ * we don't disable KFENCE without making an allocation.
+ */
+ if (size > PAGE_SIZE)
+ return NULL;
+
+ /*
* allocation_gate only needs to become non-zero, so it doesn't make
* sense to continue writing to it and pay the associated contention
* cost, in case we have a large number of concurrent allocations.
@@ -757,9 +764,6 @@ void *__kfence_alloc(struct kmem_cache *
if (!READ_ONCE(kfence_enabled))
return NULL;

- if (size > PAGE_SIZE)
- return NULL;
-
return kfence_guarded_alloc(s, size, flags);
}


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