drbd: Convert from ahash to shash

In preparing to remove all stack VLA usage from the kernel[1], this
removes the discouraged use of AHASH_REQUEST_ON_STACK in favor of
the smaller SHASH_DESC_ON_STACK by converting from ahash-wrapped-shash
to direct shash. By removing a layer of indirection this both improves
performance and reduces stack usage. The stack allocation will be made
a fixed size in a later patch to the crypto subsystem.

The bulk of the lines in this change are simple s/ahash/shash/, but the
main logic differences are in drbd_csum_ee() and drbd_csum_bio(), which
externalizes the page walking with k(un)map_atomic() instead of using
scattergather.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Acked-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 32 insertions, 31 deletions

diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index b8f77e83d456..c7ef48efe871 100644
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -295,60 +295,61 @@ void drbd_request_endio(struct bio *bio)
 		complete_master_bio(device, &m);
 }
 
-void drbd_csum_ee(struct crypto_ahash *tfm, struct drbd_peer_request *peer_req, void *digest)
+void drbd_csum_ee(struct crypto_shash *tfm, struct drbd_peer_request *peer_req, void *digest)
 {
-	AHASH_REQUEST_ON_STACK(req, tfm);
-	struct scatterlist sg;
+	SHASH_DESC_ON_STACK(desc, tfm);
 	struct page *page = peer_req->pages;
 	struct page *tmp;
 	unsigned len;
+	void *src;
 
-	ahash_request_set_tfm(req, tfm);
-	ahash_request_set_callback(req, 0, NULL, NULL);
+	desc->tfm = tfm;
+	desc->flags = 0;
 
-	sg_init_table(&sg, 1);
-	crypto_ahash_init(req);
+	crypto_shash_init(desc);
 
+	src = kmap_atomic(page);
 	while ((tmp = page_chain_next(page))) {
 		/* all but the last page will be fully used */
-		sg_set_page(&sg, page, PAGE_SIZE, 0);
-		ahash_request_set_crypt(req, &sg, NULL, sg.length);
-		crypto_ahash_update(req);
+		crypto_shash_update(desc, src, PAGE_SIZE);
+		kunmap_atomic(src);
 		page = tmp;
+		src = kmap_atomic(page);
 	}
 	/* and now the last, possibly only partially used page */
 	len = peer_req->i.size & (PAGE_SIZE - 1);
-	sg_set_page(&sg, page, len ?: PAGE_SIZE, 0);
-	ahash_request_set_crypt(req, &sg, digest, sg.length);
-	crypto_ahash_finup(req);
-	ahash_request_zero(req);
+	crypto_shash_update(desc, src, len ?: PAGE_SIZE);
+	kunmap_atomic(src);
+
+	crypto_shash_final(desc, digest);
+	shash_desc_zero(desc);
 }
 
-void drbd_csum_bio(struct crypto_ahash *tfm, struct bio *bio, void *digest)
+void drbd_csum_bio(struct crypto_shash *tfm, struct bio *bio, void *digest)
 {
-	AHASH_REQUEST_ON_STACK(req, tfm);
-	struct scatterlist sg;
+	SHASH_DESC_ON_STACK(desc, tfm);
 	struct bio_vec bvec;
 	struct bvec_iter iter;
 
-	ahash_request_set_tfm(req, tfm);
-	ahash_request_set_callback(req, 0, NULL, NULL);
+	desc->tfm = tfm;
+	desc->flags = 0;
 
-	sg_init_table(&sg, 1);
-	crypto_ahash_init(req);
+	crypto_shash_init(desc);
 
 	bio_for_each_segment(bvec, bio, iter) {
-		sg_set_page(&sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
-		ahash_request_set_crypt(req, &sg, NULL, sg.length);
-		crypto_ahash_update(req);
+		u8 *src;
+
+		src = kmap_atomic(bvec.bv_page);
+		crypto_shash_update(desc, src + bvec.bv_offset, bvec.bv_len);
+		kunmap_atomic(src);
+
 		/* REQ_OP_WRITE_SAME has only one segment,
 		 * checksum the payload only once. */
 		if (bio_op(bio) == REQ_OP_WRITE_SAME)
 			break;
 	}
-	ahash_request_set_crypt(req, NULL, digest, 0);
-	crypto_ahash_final(req);
-	ahash_request_zero(req);
+	crypto_shash_final(desc, digest);
+	shash_desc_zero(desc);
 }
 
 /* MAYBE merge common code with w_e_end_ov_req */
@@ -367,7 +368,7 @@ static int w_e_send_csum(struct drbd_work *w, int cancel)
 	if (unlikely((peer_req->flags & EE_WAS_ERROR) != 0))
 		goto out;
 
-	digest_size = crypto_ahash_digestsize(peer_device->connection->csums_tfm);
+	digest_size = crypto_shash_digestsize(peer_device->connection->csums_tfm);
 	digest = kmalloc(digest_size, GFP_NOIO);
 	if (digest) {
 		sector_t sector = peer_req->i.sector;
@@ -1205,7 +1206,7 @@ int w_e_end_csum_rs_req(struct drbd_work *w, int cancel)
 		 * a real fix would be much more involved,
 		 * introducing more locking mechanisms */
 		if (peer_device->connection->csums_tfm) {
-			digest_size = crypto_ahash_digestsize(peer_device->connection->csums_tfm);
+			digest_size = crypto_shash_digestsize(peer_device->connection->csums_tfm);
 			D_ASSERT(device, digest_size == di->digest_size);
 			digest = kmalloc(digest_size, GFP_NOIO);
 		}
@@ -1255,7 +1256,7 @@ int w_e_end_ov_req(struct drbd_work *w, int cancel)
 	if (unlikely(cancel))
 		goto out;
 
-	digest_size = crypto_ahash_digestsize(peer_device->connection->verify_tfm);
+	digest_size = crypto_shash_digestsize(peer_device->connection->verify_tfm);
 	digest = kmalloc(digest_size, GFP_NOIO);
 	if (!digest) {
 		err = 1;	/* terminate the connection in case the allocation failed */
@@ -1327,7 +1328,7 @@ int w_e_end_ov_reply(struct drbd_work *w, int cancel)
 	di = peer_req->digest;
 
 	if (likely((peer_req->flags & EE_WAS_ERROR) == 0)) {
-		digest_size = crypto_ahash_digestsize(peer_device->connection->verify_tfm);
+		digest_size = crypto_shash_digestsize(peer_device->connection->verify_tfm);
 		digest = kmalloc(digest_size, GFP_NOIO);
 		if (digest) {
 			drbd_csum_ee(peer_device->connection->verify_tfm, peer_req, digest);