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SubjectRE: [PATCH] crypto: gcm - fix cacheline sharing
Date
> 
> This might work:
>
> diff --git a/drivers/crypto/caam/caamalg.c b/drivers/crypto/caam/caamalg.c
> index c0ece44f303b..3d313d2a279a 100644
> --- a/drivers/crypto/caam/caamalg.c
> +++ b/drivers/crypto/caam/caamalg.c
> @@ -1661,7 +1661,8 @@ static int aead_decrypt(struct aead_request *req)
> * allocate and map the skcipher extended descriptor for skcipher
> */
> static struct skcipher_edesc *skcipher_edesc_alloc(struct
> skcipher_request *req,
> - int desc_bytes)
> + int desc_bytes,
> + u8 const *input_iv)
> {
> struct crypto_skcipher *skcipher = crypto_skcipher_reqtfm(req);
> struct caam_ctx *ctx = crypto_skcipher_ctx(skcipher);
> @@ -1745,7 +1746,7 @@ static struct skcipher_edesc
> *skcipher_edesc_alloc(struct skcipher_request *req,
> /* Make sure IV is located in a DMAable area */
> if (ivsize) {
> iv = (u8 *)edesc->hw_desc + desc_bytes + sec4_sg_bytes;
> - memcpy(iv, req->iv, ivsize);
> + memcpy(iv, input_iv, ivsize);
>
> iv_dma = dma_map_single(jrdev, iv, ivsize, DMA_TO_DEVICE);
> if (dma_mapping_error(jrdev, iv_dma)) {
> @@ -1801,7 +1802,8 @@ static int skcipher_encrypt(struct skcipher_request
> *req)
> int ret = 0;
>
> /* allocate extended descriptor */
> - edesc = skcipher_edesc_alloc(req, DESC_JOB_IO_LEN * CAAM_CMD_SZ);
> + edesc = skcipher_edesc_alloc(req, DESC_JOB_IO_LEN * CAAM_CMD_SZ,
> + req->iv);
> if (IS_ERR(edesc))
> return PTR_ERR(edesc);
>
> @@ -1832,13 +1834,11 @@ static int skcipher_decrypt(struct
> skcipher_request *req)
> struct caam_ctx *ctx = crypto_skcipher_ctx(skcipher);
> int ivsize = crypto_skcipher_ivsize(skcipher);
> struct device *jrdev = ctx->jrdev;
> + u8 in_iv[AES_BLOCK_SIZE];
> u32 *desc;
> int ret = 0;
>
> - /* allocate extended descriptor */
> - edesc = skcipher_edesc_alloc(req, DESC_JOB_IO_LEN * CAAM_CMD_SZ);
> - if (IS_ERR(edesc))
> - return PTR_ERR(edesc);
> + memcpy(in_iv, req->iv, ivsize);
>
> /*
> * The crypto API expects us to set the IV (req->iv) to the last
> @@ -1848,6 +1848,11 @@ static int skcipher_decrypt(struct skcipher_request
> *req)
> scatterwalk_map_and_copy(req->iv, req->src, req->cryptlen
> -
> ivsize, ivsize, 0);
>
> + /* allocate extended descriptor */
> + edesc = skcipher_edesc_alloc(req, DESC_JOB_IO_LEN * CAAM_CMD_SZ,
> in_iv);
> + if (IS_ERR(edesc))
> + return PTR_ERR(edesc);
> +
> /* Create and submit job descriptor*/
> init_skcipher_job(req, edesc, false);
> desc = edesc->hw_desc;

Interesting. This discussion made me reevaluate my own implementation.

First thing I realised is that I *am* currently doing the IV copying with
the data buffer mapped for DMA ... If I understand correctly that may be a
bad idea on some systems? I which case I will need to do my copy earlier.

Second thing is the above implementation made me realise I don't need to
buffer the IV as part of the skcipher_request_ctx, I can just copy the
original req->iv to some local variable, pass a pointer to that along and
then overwrite req->iv directly. More elegant and hopefully also more
efficient ...

Regards,
Pascal van Leeuwen
Silicon IP Architect, Multi-Protocol Engines
www.insidesecure.com


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