linux-kernel - Re: [PATCH] mm: kfence: Fix false positives on big endian

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Date:   Fri, 5 May 2023 09:43:46 +0200
From:   Marco Elver <elver@...gle.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     glider@...gle.com, akpm@...ux-foundation.org,
        zhangpeng.00@...edance.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] mm: kfence: Fix false positives on big endian

On Fri, 5 May 2023 at 05:51, Michael Ellerman <mpe@...erman.id.au> wrote:
>
> 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@...erman.id.au>

Reviewed-by: Marco Elver <elver@...gle.com>

Andrew, is the Fixes enough to make it to stable as well or do we also
need Cc: stable?

Thanks,
-- Marco

> ---
>  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)))
>
>  /* Maximum stack depth for reports. */
>  #define KFENCE_STACK_DEPTH 64
> --
> 2.40.1
>