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kfence: move the size check to the beginning of __kfence_alloc()

PATCH Applied Alexander Potapenko 1 participant 2 messages Jul 14, 2021

Subsystems (3)
Stable branch Memory management Kfence
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Alexander Potapenko

author maintainer
#0 lore raw

PATCH 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(-)
mm/kfence/core.c +7 -3
index d7666ace9d2e4..2623ff401a104 100644
@@ -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);
 }
Signature · 1 line
2.32.0.93.g670b81a890-goog
author maintainer
#1 lore raw

PATCH 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(+)
mm/kfence/core.c +9 -0
index 2623ff401a104..575c685aa6422 100644
@@ -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
Signature · 1 line
2.32.0.93.g670b81a890-goog