Re: [PATCH] crypto: atmel-ecc - reject hardware ECDH without a public key

[Thorsten Blum <thorsten.blum@linux.dev>]

On Thu, Jun 11, 2026 at 11:36:17PM +0200, Thorsten Blum wrote:
> The hardware ECDH path in atmel_ecdh_compute_shared_secret() uses the
> private key stored in the device. However, the public key is cached only
> after atmel_ecdh_set_secret() successfully generated that private key
> for the current tfm.
> 
> atmel_ecdh_generate_public_key() already rejects requests when no public
> key is cached. Add the same check to atmel_ecdh_compute_shared_secret()
> to prevent the device from using a private key that was not generated
> for the current tfm.
> 
> Fixes: 11105693fa05 ("crypto: atmel-ecc - introduce Microchip / Atmel ECC driver")
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> ---
>  drivers/crypto/atmel-ecc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/crypto/atmel-ecc.c b/drivers/crypto/atmel-ecc.c
> index 93f219558c2f..542c8cc13a0f 100644
> --- a/drivers/crypto/atmel-ecc.c
> +++ b/drivers/crypto/atmel-ecc.c
> @@ -173,6 +173,9 @@ static int atmel_ecdh_compute_shared_secret(struct kpp_request *req)
>  		return crypto_kpp_compute_shared_secret(req);
>  	}
>  
> +	if (!ctx->public_key)
> +		return -EINVAL;
> +
>  	/* must have exactly two points to be on the curve */
>  	if (req->src_len != ATMEL_ECC_PUBKEY_SIZE)
>  		return -EINVAL;

I'll need to rebase and resend this assuming [1] is applied first, as it
currently doesn't apply cleanly.

[1] https://lore.kernel.org/lkml/20260609100552.233494-3-thorsten.blum@linux.dev/