2021-07-14 09:23:27

by Alexander Potapenko

Subject: [PATCH mm v5 1/2] kfence: move the size check to the beginning of __kfence_alloc()

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.

Suggested-by: Marco Elver <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: [email protected] # 5.12+
Signed-off-by: Alexander Potapenko <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
---
mm/kfence/core.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index d7666ace9d2e4..2623ff401a104 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -733,6 +733,13 @@ void kfence_shutdown_cache(struct kmem_cache *s)

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
@@ -757,9 +764,6 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
if (!READ_ONCE(kfence_enabled))
return NULL;

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

--
2.32.0.93.g670b81a890-goog

2021-07-14 09:24:40

by Alexander Potapenko

Subject: [PATCH mm v5 2/2] kfence: skip all GFP_ZONEMASK allocations

Allocation requests outside ZONE_NORMAL (MOVABLE, HIGHMEM or DMA) cannot
be fulfilled by KFENCE, because KFENCE memory pool is located in a
zone different from the requested one.

Because callers of kmem_cache_alloc() may actually rely on the
allocation to reside in the requested zone (e.g. memory allocations done
with __GFP_DMA must be DMAable), skip all allocations done with
GFP_ZONEMASK and/or respective SLAB flags (SLAB_CACHE_DMA and
SLAB_CACHE_DMA32).

Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Cc: Andrew Morton <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Souptick Joarder <[email protected]>
Cc: [email protected] # 5.12+
Signed-off-by: Alexander Potapenko <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
Acked-by: Souptick Joarder <[email protected]>

---

v2:
- added parentheses around the GFP clause, as requested by Marco
v3:
- ignore GFP_ZONEMASK, which also covers __GFP_HIGHMEM and __GFP_MOVABLE
- move the flag check at the beginning of the function, as requested by
Souptick Joarder
v4:
- minor fixes to description and comment formatting
v5:
- pick Acked-by:, rebase
---
mm/kfence/core.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 2623ff401a104..575c685aa6422 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -740,6 +740,15 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
if (size > PAGE_SIZE)
return NULL;

+ /*
+ * Skip allocations from non-default zones, including DMA. We cannot
+ * guarantee that pages in the KFENCE pool will have the requested
+ * properties (e.g. reside in DMAable memory).
+ */
+ if ((flags & GFP_ZONEMASK) ||
+ (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32)))
+ 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
--
2.32.0.93.g670b81a890-goog