[PATCH v5 13/15] crypto: ti - Correct AEAD tag operations against dma cache invalidation

[T Pratham <t-pratham@ti.com>]

There are two issues wrt tag operations (tag read/write in AEAD
algorithms) pointed out by Sashiko:
1. dma_sync_sg_for_cpu() before tag operations always uses rx_dev. But
   dst is mapped with tx_dev in case of inline operations. This is
   "technically" a no-issue right now as both devices use different
   channels from the same dma device. But it is nice to be correct.
2. dma_unmap_sg() is being called after tag operations. But between
   them, there is no synchronisation step. So tag operations writing TAG
   into the dst scatterlist could in theory be lost in the cache
   invalidation done as part of unmapping scatterlists.

Now, in the current code, we can correct both of these with some
conditional logic and repeating the sync (this time with
sync_for_device). However, it felt more elegant to move the TAG
operations to occur after all the scatterlists are unmapped. This
ensures all buffers are properly synced as well as avoids unnecessary
repeated syncing of caches.

Fixes: 37b902c603042 ("crypto: ti - Add support for AES-GCM in DTHEv2 driver")
Signed-off-by: T Pratham <t-pratham@ti.com>
---
 drivers/crypto/ti/dthev2-aes.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/crypto/ti/dthev2-aes.c b/drivers/crypto/ti/dthev2-aes.c
index 150ce65f613fa..150ba73776aa9 100644
--- a/drivers/crypto/ti/dthev2-aes.c
+++ b/drivers/crypto/ti/dthev2-aes.c
@@ -913,6 +913,7 @@ static int dthe_aead_run(struct crypto_engine *engine, void *areq)
 	struct device *tx_dev, *rx_dev;
 	struct dma_async_tx_descriptor *desc_in, *desc_out, *desc_aad_out;
 	bool cleanup_tx_chan = false;
+	bool do_tag_ops = false;
 
 	int ret;
 	int err;
@@ -1136,15 +1137,11 @@ static int dthe_aead_run(struct crypto_engine *engine, void *areq)
 		ret = 0;
 	}
 
-	if (cryptlen != 0)
-		dma_sync_sg_for_cpu(rx_dev, dst, dst_nents, dst_dir);
-
-	if (rctx->enc)
-		err = dthe_aead_enc_get_tag(req);
-	else
-		err = dthe_aead_dec_verify_tag(req);
-
-	ret = (ret) ? ret : err;
+	/*
+	 * Need to read TAG registers if data is submitted, even in case
+	 * of DMA timeout, to clear the hardware states
+	 */
+	do_tag_ops = true;
 
 aead_dma_prep_dst_err:
 	if (diff_dst && cryptlen != 0)
@@ -1160,6 +1157,16 @@ static int dthe_aead_run(struct crypto_engine *engine, void *areq)
 	if (assoclen != 0)
 		dma_unmap_sg(tx_dev, aad_sg, aad_nents, aad_dir);
 
+	/* Do tag ops after scatterlist unmapping syncs caches */
+	if (do_tag_ops) {
+		if (rctx->enc)
+			err = dthe_aead_enc_get_tag(req);
+		else
+			err = dthe_aead_dec_verify_tag(req);
+
+		ret = (ret) ? ret : err;
+	}
+
 aead_dma_map_aad_err:
 	if (diff_dst && cryptlen != 0)
 		kfree(dst);
-- 
2.34.1