Thread (9 messages) 9 messages, 7 authors, 2023-05-19

RE: [PATCH] mm: kfence: Fix false positives on big endian

From: David Laight <hidden>
Date: 2023-05-05 16:02:27
Also in: linux-mm, lkml

From: Michael Ellerman
quoted hunk ↗ jump to hunk
Sent: 05 May 2023 04:51

Since commit 1ba3cbf3ec3b ("mm: kfence: improve the performance of
__kfence_alloc() and __kfence_free()"), kfence reports failures in
random places at boot on big endian machines.

The problem is that the new KFENCE_CANARY_PATTERN_U64 encodes the
address of each byte in its value, so it needs to be byte swapped on big
endian machines.

The compiler is smart enough to do the le64_to_cpu() at compile time, so
there is no runtime overhead.

Fixes: 1ba3cbf3ec3b ("mm: kfence: improve the performance of __kfence_alloc() and __kfence_free()")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 mm/kfence/kfence.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h
index 2aafc46a4aaf..392fb273e7bd 100644
--- a/mm/kfence/kfence.h
+++ b/mm/kfence/kfence.h
@@ -29,7 +29,7 @@
  * canary of every 8 bytes is the same. 64-bit memory can be filled and checked
  * at a time instead of byte by byte to improve performance.
  */
-#define KFENCE_CANARY_PATTERN_U64 ((u64)0xaaaaaaaaaaaaaaaa ^ (u64)(0x0706050403020100))
+#define KFENCE_CANARY_PATTERN_U64 ((u64)0xaaaaaaaaaaaaaaaa ^ (u64)(le64_to_cpu(0x0706050403020100)))
What at the (u64) casts for?
The constants should probably have a ul (or ull) suffix.

	David

-
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