[v8,1/3] crypto: scatterwak - Add scatterwalk_sg_copychunks

Commit Message

Tudor Ambarus June 15, 2016, 2:52 p.m. UTC

This patch adds the function scatterwalk_sg_copychunks which writes
a chunk of data from a scatterwalk to another scatterwalk.
It will be used by caam driver to remove the leading zeros
for the output data of the RSA algorithm, after the computation completes.

Signed-off-by: Tudor Ambarus <[e-mail]>
---
 crypto/scatterwalk.c         | 26 ++++++++++++++++++++++++++
 include/crypto/scatterwalk.h |  2 ++
 2 files changed, 28 insertions(+)

Comments

Herbert Xu June 20, 2016, 10:54 a.m. UTC | #1

On Wed, Jun 15, 2016 at 05:52:42PM +0300, Tudor Ambarus wrote:
> This patch adds the function scatterwalk_sg_copychunks which writes
> a chunk of data from a scatterwalk to another scatterwalk.
> It will be used by caam driver to remove the leading zeros
> for the output data of the RSA algorithm, after the computation completes.
> 
> Signed-off-by: Tudor Ambarus <[e-mail]>

Not only does dropping leading zeroes lead to questions about
information leaks, but it makes every one of our RSA drivers
look crap.

So I'm going to change this and make it not skip leading zeroes.

Thanks,

Patch

diff --git a/crypto/scatterwalk.c b/crypto/scatterwalk.c
index ea5815c..bc3222d 100644
--- a/crypto/scatterwalk.c
+++ b/crypto/scatterwalk.c
@@ -125,6 +125,32 @@  void scatterwalk_map_and_copy(void *buf, struct scatterlist *sg,
 }
 EXPORT_SYMBOL_GPL(scatterwalk_map_and_copy);
 
+void scatterwalk_sg_copychunks(struct scatter_walk *dest,
+			       struct scatter_walk *src, size_t nbytes)
+{
+	for (;;) {
+		unsigned int len_this_page = scatterwalk_pagelen(dest);
+		u8 *vaddr;
+
+		if (len_this_page > nbytes)
+			len_this_page = nbytes;
+
+		vaddr = scatterwalk_map(dest);
+		scatterwalk_copychunks(vaddr, src, len_this_page, 0);
+		scatterwalk_unmap(vaddr);
+
+		scatterwalk_advance(dest, len_this_page);
+
+		if (nbytes == len_this_page)
+			break;
+
+		nbytes -= len_this_page;
+
+		scatterwalk_pagedone(dest, 0, 1);
+	}
+}
+EXPORT_SYMBOL_GPL(scatterwalk_sg_copychunks);
+
 int scatterwalk_bytes_sglen(struct scatterlist *sg, int num_bytes)
 {
 	int offset = 0, n = 0;
diff --git a/include/crypto/scatterwalk.h b/include/crypto/scatterwalk.h
index 35f99b6..8b799c5 100644
--- a/include/crypto/scatterwalk.h
+++ b/include/crypto/scatterwalk.h
@@ -86,6 +86,8 @@  static inline void scatterwalk_unmap(void *vaddr)
 void scatterwalk_start(struct scatter_walk *walk, struct scatterlist *sg);
 void scatterwalk_copychunks(void *buf, struct scatter_walk *walk,
 			    size_t nbytes, int out);
+void scatterwalk_sg_copychunks(struct scatter_walk *dest,
+			       struct scatter_walk *src, size_t nbytes);
 void *scatterwalk_map(struct scatter_walk *walk);
 void scatterwalk_done(struct scatter_walk *walk, int out, int more);