Subject: Re: [PATCH v2 10/29] crypto: powerpc/p10-aes-gcm - simplify handling of linear associated data

From: Eric Biggers <[email-masked]>
Date: Thu, 2 Jan 2025 17:24:44 +0000

On Thu, Jan 02, 2025 at 12:50:50PM +0100, Christophe Leroy wrote:
> 
> 
> Le 30/12/2024 à 01:13, Eric Biggers a écrit :
> > From: Eric Biggers <[email-masked]>
> > 
> > p10_aes_gcm_crypt() is abusing the scatter_walk API to get the virtual
> > address for the first source scatterlist element.  But this code is only
> > built for PPC64 which is a !HIGHMEM platform, and it can read past a
> > page boundary from the address returned by scatterwalk_map() which means
> > it already assumes the address is from the kernel's direct map.  Thus,
> > just use sg_virt() instead to get the same result in a simpler way.
> > 
> > Cc: Christophe Leroy <[email-masked]>
> > Cc: Danny Tsen <[email-masked]>
> > Cc: Michael Ellerman <[email-masked]>
> > Cc: Naveen N Rao <[email-masked]>
> > Cc: Nicholas Piggin <[email-masked]>
> > Cc: [email-masked]
> > Signed-off-by: Eric Biggers <[email-masked]>
> > ---
> > 
> > This patch is part of a long series touching many files, so I have
> > limited the Cc list on the full series.  If you want the full series and
> > did not receive it, please retrieve it from lore.kernel.org.
> > 
> >   arch/powerpc/crypto/aes-gcm-p10-glue.c | 8 ++------
> >   1 file changed, 2 insertions(+), 6 deletions(-)
> > 
> > diff --git a/arch/powerpc/crypto/aes-gcm-p10-glue.c b/arch/powerpc/crypto/aes-gcm-p10-glue.c
> > index f37b3d13fc53..2862c3cf8e41 100644
> > --- a/arch/powerpc/crypto/aes-gcm-p10-glue.c
> > +++ b/arch/powerpc/crypto/aes-gcm-p10-glue.c
> > @@ -212,11 +212,10 @@ static int p10_aes_gcm_crypt(struct aead_request *req, u8 *riv,
> >   	struct p10_aes_gcm_ctx *ctx = crypto_tfm_ctx(tfm);
> >   	u8 databuf[sizeof(struct gcm_ctx) + PPC_ALIGN];
> >   	struct gcm_ctx *gctx = PTR_ALIGN((void *)databuf, PPC_ALIGN);
> >   	u8 hashbuf[sizeof(struct Hash_ctx) + PPC_ALIGN];
> >   	struct Hash_ctx *hash = PTR_ALIGN((void *)hashbuf, PPC_ALIGN);
> > -	struct scatter_walk assoc_sg_walk;
> >   	struct skcipher_walk walk;
> >   	u8 *assocmem = NULL;
> >   	u8 *assoc;
> >   	unsigned int cryptlen = req->cryptlen;
> >   	unsigned char ivbuf[AES_BLOCK_SIZE+PPC_ALIGN];
> > @@ -232,12 +231,11 @@ static int p10_aes_gcm_crypt(struct aead_request *req, u8 *riv,
> >   	memset(ivbuf, 0, sizeof(ivbuf));
> >   	memcpy(iv, riv, GCM_IV_SIZE);
> >   	/* Linearize assoc, if not already linear */
> >   	if (req->src->length >= assoclen && req->src->length) {
> > -		scatterwalk_start(&assoc_sg_walk, req->src);
> > -		assoc = scatterwalk_map(&assoc_sg_walk);
> > +		assoc = sg_virt(req->src); /* ppc64 is !HIGHMEM */
> >   	} else {
> >   		gfp_t flags = (req->base.flags & CRYPTO_TFM_REQ_MAY_SLEEP) ?
> >   			      GFP_KERNEL : GFP_ATOMIC;
> >   		/* assoc can be any length, so must be on heap */
> > @@ -251,13 +249,11 @@ static int p10_aes_gcm_crypt(struct aead_request *req, u8 *riv,
> >   	vsx_begin();
> >   	gcmp10_init(gctx, iv, (unsigned char *) &ctx->enc_key, hash, assoc, assoclen);
> >   	vsx_end();
> > -	if (!assocmem)
> > -		scatterwalk_unmap(assoc);
> > -	else
> > +	if (assocmem)
> >   		kfree(assocmem);
> 
> kfree() accepts a NULL pointer, you can call kfree(assocmem) without 'if
> (assocmem)'

The existing code did that too, but sure I'll change that in v3.

- Eric