Re: [PATCH v5] crypto: rsassa-pkcs1 - Avoid cacheline sharing with underlying driver

[Herbert Xu]

On Fri, Jul 31, 2026 at 12:44:46PM +1000, Changwei Zou wrote:
> out_buf is used as a DMA buffer for the RSA verification operation.
> If it is not aligned to CRYPTO_DMA_ALIGN, cacheline sharing
> problems (data corruption) would occur on CPUs with DMA-incoherent caches,
> leading to -EKEYREJECTED.
> 
> Rename out_buf to buf, as it serves as both the input and output buffer.
> Add a buf_ptr pointer to track its position.
> 
> Allocate the buffer separately via kmalloc(), which guarantees cacheline
> alignment on architectures without fully coherent DMA.
> This acts as a defensive measure, and avoids the need for an extra copy
> in the underlying driver, which should check alignment before supplying
> buffers to the hardware.
> 
> The intermittent error 'Key was rejected by service' on i.MX8 with CAAM
> can be triggered when loading signed kernel modules.
> 
>     for i in $(seq 1 100); do
>         sudo modprobe xfs 2>&1 && echo "SUCCESS on attempt $i" \
>         && sudo rmmod xfs || echo "FAILED on attempt $i"
>     done
> 
> Signed-off-by: Changwei Zou <changwei.zou@xxxxxxxxxxxxx>
> ---
>  crypto/rsassa-pkcs1.c | 31 ++++++++++++++++---------------
>  1 file changed, 16 insertions(+), 15 deletions(-)

In the Crypto API we don't ask the user to provide aligned data.

In general it's the driver's responsibility to ensure proper
alignment.  Which driver are we talking about here?

Thanks,
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
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