crypto: powerpc/p10-aes-gcm - simplify handling of linear associated data

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 <christophe.leroy@csgroup.eu>
Cc: Danny Tsen <dtsen@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Naveen N Rao <naveen@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Author: ebiggers

arch/powerpc/crypto/aes-gcm-p10-glue.c

@@ -214,7 +214,6 @@ static int p10_aes_gcm_crypt(struct aead_request *req, u8 *riv,
 	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;
@@ -234,8 +233,7 @@ static int p10_aes_gcm_crypt(struct aead_request *req, u8 *riv,
 
 	/* 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;
@@ -253,10 +251,7 @@ static int p10_aes_gcm_crypt(struct aead_request *req, u8 *riv,
 	gcmp10_init(gctx, iv, (unsigned char *) &ctx->enc_key, hash, assoc, assoclen);
 	vsx_end();
 
-	if (!assocmem)
-		scatterwalk_unmap(assoc);
-	else
-		kfree(assocmem);
+	kfree(assocmem);
 
 	if (enc)
 		ret = skcipher_walk_aead_encrypt(&walk, req, false);