Re: [PATCH] crypto: gcm - fix cacheline sharing

[Ard Biesheuvel]

On Thu, 30 May 2019 at 16:28, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
>
> On Thu, 30 May 2019 at 16:27, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > On Thu, May 30, 2019 at 03:55:07PM +0200, Ard Biesheuvel wrote:
> > >
> > > > Would this work?
> >
> > I see.  You need to preserve the original IV.
> >
> > > > diff --git a/drivers/crypto/caam/caamalg.c b/drivers/crypto/caam/caamalg.c
> > > > index c0ece44f303b..2ef2f76a3cb8 100644
> > > > --- a/drivers/crypto/caam/caamalg.c
> > > > +++ b/drivers/crypto/caam/caamalg.c
> > > > @@ -1832,22 +1832,25 @@ 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 out_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);
> > > > -
> > > >         /*
> > > >          * The crypto API expects us to set the IV (req->iv) to the last
> > > >          * ciphertext block.
> > > >          */
> > > >         if (ivsize)
> > > > -               scatterwalk_map_and_copy(req->iv, req->src, req->cryptlen -
> > > > +               scatterwalk_map_and_copy(out_iv, req->src, req->cryptlen -
> > > >                                          ivsize, ivsize, 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(req->iv, out_iv, ivsize);
> > > > +
> > > >         /* Create and submit job descriptor*/
> > > >         init_skcipher_job(req, edesc, false);
> > > >         desc = edesc->hw_desc;
> > >
> > > Umm never mind
> > >
> > > /me hides in shame
> >
> > So why doesn't this work?
> >
>
> Because the memcpy() occurs while the buffer is mapped for DMA, so it
> suffers from the exact same problem.

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;