Re: [PATCH] crypto: caam - Use bounce buffer for unaligned RSA destination buffers

[Herbert Xu <herbert@gondor.apana.org.au>]

On Wed, Aug 05, 2026 at 02:19:02PM +1000, Changwei Zou wrote:
> The CAAM RSA driver directly DMA-maps the destination buffer supplied by
> the caller via req->dst without checking whether it meets the cacheline
> alignment requirements of DMA-incoherent hardware such as i.MX8.
> 
> On CPUs with non-coherent DMA caches, if the destination buffer shares a
> cacheline with other data (i.e. it is not cacheline-aligned), cache
> writeback/invalidation during DMA can corrupt adjacent memory or cause
> stale data to be read back. This manifests as intermittent -EKEYREJECTED
> errors when loading signed kernel modules.
> 
> When any segment of req->dst is not cacheline-aligned, allocate a
> single contiguous aligned bounce buffer covering the full dst_len,
> redirect the operation to it, and scatter-copy the result back to the
> original destination once the hardware has completed the operation.
> 
> 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@canonical.com>
> Assisted-by: OpenCode:claude-sonnet-4.6
> ---
>  drivers/crypto/caam/caampkc.c | 66 ++++++++++++++++++++++++++++++++++-
>  drivers/crypto/caam/caampkc.h |  6 ++++
>  2 files changed, 71 insertions(+), 1 deletion(-)

Please take a look at the Sashiko reviews:

https://sashiko.dev/#/patchset/20260805041902.1575170-1-changwei.zou%40canonical.com

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