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From:   David Howells <dhowells@redhat.com>
To:     Jeff Layton <jlayton@kernel.org>, Steve French <smfrench@gmail.com>
Cc:     David Howells <dhowells@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Marc Dionne <marc.dionne@auristor.com>,
        Paulo Alcantara <pc@manguebit.com>,
        Shyam Prasad N <sprasad@microsoft.com>,
        Tom Talpey <tom@talpey.com>,
        Dominique Martinet <asmadeus@codewreck.org>,
        Ilya Dryomov <idryomov@gmail.com>,
        Christian Brauner <christian@brauner.io>,
        linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org,
        linux-nfs@vger.kernel.org, ceph-devel@vger.kernel.org,
        v9fs@lists.linux.dev, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-cachefs@redhat.com
Subject: [RFC PATCH 37/53] netfs: Support decryption on ubuffered/DIO read
Date:   Fri, 13 Oct 2023 17:04:06 +0100
Message-ID: <20231013160423.2218093-38-dhowells@redhat.com>
In-Reply-To: <20231013160423.2218093-1-dhowells@redhat.com>
References: <20231013160423.2218093-1-dhowells@redhat.com>
MIME-Version: 1.0
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Support unbuffered and direct I/O reads from an encrypted file.  This may
require making a larger read than is required into a bounce buffer and
copying out the required bits.  We don't decrypt in-place in the user
buffer lest userspace interfere and muck up the decryption.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
---
 fs/netfs/direct_read.c | 10 ++++++++++
 fs/netfs/internal.h    | 17 +++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/fs/netfs/direct_read.c b/fs/netfs/direct_read.c
index 52ad8fa66dd5..158719b56900 100644
--- a/fs/netfs/direct_read.c
+++ b/fs/netfs/direct_read.c
@@ -181,6 +181,16 @@ static ssize_t netfs_unbuffered_read_iter_locked(struct kiocb *iocb, struct iov_
 		iov_iter_advance(iter, orig_count);
 	}
 
+	/* If we're going to do decryption or decompression, we're going to
+	 * need a bounce buffer - and if the data is misaligned for the crypto
+	 * algorithm, we decrypt in place and then copy.
+	 */
+	if (test_bit(NETFS_RREQ_CONTENT_ENCRYPTION, &rreq->flags)) {
+		if (!netfs_is_crypto_aligned(rreq, iter))
+			__set_bit(NETFS_RREQ_CRYPT_IN_PLACE, &rreq->flags);
+		__set_bit(NETFS_RREQ_USE_BOUNCE_BUFFER, &rreq->flags);
+	}
+
 	/* If we're going to use a bounce buffer, we need to set it up.  We
 	 * will then need to pad the request out to the minimum block size.
 	 */
diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 8dc68a75d6cd..7dd37d3aff3f 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -196,6 +196,23 @@ static inline void netfs_put_group_many(struct netfs_group *netfs_group, int nr)
 		netfs_group->free(netfs_group);
 }
 
+/*
+ * Check to see if a buffer aligns with the crypto unit block size.  If it
+ * doesn't the crypto layer is going to copy all the data - in which case
+ * relying on the crypto op for a free copy is pointless.
+ */
+static inline bool netfs_is_crypto_aligned(struct netfs_io_request *rreq,
+					   struct iov_iter *iter)
+{
+	struct netfs_inode *ctx = netfs_inode(rreq->inode);
+	unsigned long align, mask = (1UL << ctx->min_bshift) - 1;
+
+	if (!ctx->min_bshift)
+		return true;
+	align = iov_iter_alignment(iter);
+	return (align & mask) == 0;
+}
+
 /*****************************************************************************/
 /*
  * debug tracing