linux-kernel - [Update PATCH 2/2] aio, mem-hotplug: Add memory barrier to aio ring page migration.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <530F3327.8020205@jp.fujitsu.com>
Date:	Thu, 27 Feb 2014 21:44:23 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Tang Chen <tangchen@...fujitsu.com>, <bcrl@...ck.org>
CC:	<viro@...iv.linux.org.uk>, <jmoyer@...hat.com>,
	<kosaki.motohiro@...il.com>, <kosaki.motohiro@...fujitsu.com>,
	<guz.fnst@...fujitsu.com>, <linux-fsdevel@...r.kernel.org>,
	<linux-aio@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: [Update PATCH 2/2] aio, mem-hotplug: Add memory barrier to aio ring
 page migration.

When doing aio ring page migration, we migrated the page, and update
ctx->ring_pages[]. Like the following:

aio_migratepage()
 |-> migrate_page_copy(new, old)
 |   ......				/* Need barrier here */
 |-> ctx->ring_pages[idx] = new

Actually, we need a memory barrier between these two operations.
Otherwise, if ctx->ring_pages[] is updated before memory copy due to
the compiler optimization, other processes may have an opportunity
to access to the not fully initialized new ring page.

So add a wmb and rmb to synchronize them.

Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>

---
 fs/aio.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/aio.c b/fs/aio.c
index 50c089c..8d9b82b 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -327,6 +327,14 @@ static int aio_migratepage(struct address_space *mapping, struct page *new,
 		pgoff_t idx;
 		spin_lock_irqsave(&ctx->completion_lock, flags);
 		migrate_page_copy(new, old);
+
+		/*
+		 * Ensure memory copy is finished before updating
+		 * ctx->ring_pages[]. Otherwise other processes may access to
+		 * new ring pages which are not fully initialized.
+		 */
+		smp_wmb();
+
 		idx = old->index;
 		if (idx < (pgoff_t)ctx->nr_pages) {
 			/* And only do the move if things haven't changed */
@@ -1074,6 +1082,12 @@ static long aio_read_events_ring(struct kioctx *ctx,
 		page = ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE];
 		pos %= AIO_EVENTS_PER_PAGE;

+		/*
+		 * Ensure that the page's data was copied from old one by
+		 * aio_migratepage().
+		 */
+		smp_rmb();
+
 		ev = kmap(page);
 		copy_ret = copy_to_user(event + ret, ev + pos,
 					sizeof(*ev) * avail);

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/