crypto: caam - strip input zeros from RSA input buffer

Sometimes the provided RSA input buffer provided is not stripped
of leading zeros. This could cause its size to be bigger than that
of the modulus, making the HW complain:

caam_jr 2142000.jr1: 40000789: DECO: desc idx 7:
Protocol Size Error - A protocol has seen an error in size. When
running RSA, pdb size N < (size of F) when no formatting is used; or
pdb size N < (F + 11) when formatting is used.

Fix the problem by stripping off the leading zero from input data
before feeding it to the CAAM accelerator.

Fixes: 8c41977 ("crypto: caam - add support for RSA algorithm")
Cc: <stable@vger.kernel.org> # 4.8+
Reported-by: Martin Townsend <mtownsend1973@gmail.com>
Link: https://lkml.kernel.org/r/CABatt_ytYORYKtApcB4izhNanEKkGFi9XAQMjHi_n-8YWoCRiw@mail.gmail.com
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Tested-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/caam/caampkc.c

@@ -166,18 +166,71 @@ static void rsa_priv_f3_done(struct device *dev, u32 *desc, u32 err,
 	akcipher_request_complete(req, err);
 }
 
+static int caam_rsa_count_leading_zeros(struct scatterlist *sgl,
+					unsigned int nbytes,
+					unsigned int flags)
+{
+	struct sg_mapping_iter miter;
+	int lzeros, ents;
+	unsigned int len;
+	unsigned int tbytes = nbytes;
+	const u8 *buff;
+
+	ents = sg_nents_for_len(sgl, nbytes);
+	if (ents < 0)
+		return ents;
+
+	sg_miter_start(&miter, sgl, ents, SG_MITER_FROM_SG | flags);
+
+	lzeros = 0;
+	len = 0;
+	while (nbytes > 0) {
+		while (len && !*buff) {
+			lzeros++;
+			len--;
+			buff++;
+		}
+
+		if (len && *buff)
+			break;
+
+		sg_miter_next(&miter);
+		buff = miter.addr;
+		len = miter.length;
+
+		nbytes -= lzeros;
+		lzeros = 0;
+	}
+
+	miter.consumed = lzeros;
+	sg_miter_stop(&miter);
+	nbytes -= lzeros;
+
+	return tbytes - nbytes;
+}
+
 static struct rsa_edesc *rsa_edesc_alloc(struct akcipher_request *req,
 					 size_t desclen)
 {
 	struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
 	struct caam_rsa_ctx *ctx = akcipher_tfm_ctx(tfm);
 	struct device *dev = ctx->dev;
+	struct caam_rsa_req_ctx *req_ctx = akcipher_request_ctx(req);
 	struct rsa_edesc *edesc;
 	gfp_t flags = (req->base.flags & CRYPTO_TFM_REQ_MAY_SLEEP) ?
 		       GFP_KERNEL : GFP_ATOMIC;
+	int sg_flags = (flags == GFP_ATOMIC) ? SG_MITER_ATOMIC : 0;
 	int sgc;
 	int sec4_sg_index, sec4_sg_len = 0, sec4_sg_bytes;
 	int src_nents, dst_nents;
+	int lzeros;
+
+	lzeros = caam_rsa_count_leading_zeros(req->src, req->src_len, sg_flags);
+	if (lzeros < 0)
+		return ERR_PTR(lzeros);
+
+	req->src_len -= lzeros;
+	req->src = scatterwalk_ffwd(req_ctx->src, req->src, lzeros);
 
 	src_nents = sg_nents_for_len(req->src, req->src_len);
 	dst_nents = sg_nents_for_len(req->dst, req->dst_len);
@@ -953,6 +1006,7 @@ static struct akcipher_alg caam_rsa = {
 	.max_size = caam_rsa_max_size,
 	.init = caam_rsa_init_tfm,
 	.exit = caam_rsa_exit_tfm,
+	.reqsize = sizeof(struct caam_rsa_req_ctx),
 	.base = {
 		.cra_name = "rsa",
 		.cra_driver_name = "rsa-caam",

drivers/crypto/caam/caampkc.h

@@ -95,6 +95,14 @@ struct caam_rsa_ctx {
 	struct device *dev;
 };
 
+/**
+ * caam_rsa_req_ctx - per request context.
+ * @src: input scatterlist (stripped of leading zeros)
+ */
+struct caam_rsa_req_ctx {
+	struct scatterlist src[2];
+};
+
 /**
  * rsa_edesc - s/w-extended rsa descriptor
  * @src_nents     : number of segments in input scatterlist