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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Juergen Gross <jgross@suse.com>, Wei Liu <wl@xen.org>,
        Sasha Levin <sashal@kernel.org>, xen-devel@lists.xenproject.org
Subject: [PATCH AUTOSEL 5.6 21/38] xen/xenbus: ensure xenbus_map_ring_valloc() returns proper grant status
Date:   Fri, 24 Apr 2020 08:22:19 -0400
Message-Id: <20200424122237.9831-21-sashal@kernel.org>
In-Reply-To: <20200424122237.9831-1-sashal@kernel.org>
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From: Juergen Gross <jgross@suse.com>

[ Upstream commit 6b51fd3f65a22e3d1471b18a1d56247e246edd46 ]

xenbus_map_ring_valloc() maps a ring page and returns the status of the
used grant (0 meaning success).

There are Xen hypervisors which might return the value 1 for the status
of a failed grant mapping due to a bug. Some callers of
xenbus_map_ring_valloc() test for errors by testing the returned status
to be less than zero, resulting in no error detected and crashing later
due to a not available ring page.

Set the return value of xenbus_map_ring_valloc() to GNTST_general_error
in case the grant status reported by Xen is greater than zero.

This is part of XSA-316.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Wei Liu <wl@xen.org>
Link: https://lore.kernel.org/r/20200326080358.1018-1-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/xen/xenbus/xenbus_client.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
index e17ca81561713..a38292ef79f6d 100644
--- a/drivers/xen/xenbus/xenbus_client.c
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -448,7 +448,14 @@ EXPORT_SYMBOL_GPL(xenbus_free_evtchn);
 int xenbus_map_ring_valloc(struct xenbus_device *dev, grant_ref_t *gnt_refs,
 			   unsigned int nr_grefs, void **vaddr)
 {
-	return ring_ops->map(dev, gnt_refs, nr_grefs, vaddr);
+	int err;
+
+	err = ring_ops->map(dev, gnt_refs, nr_grefs, vaddr);
+	/* Some hypervisors are buggy and can return 1. */
+	if (err > 0)
+		err = GNTST_general_error;
+
+	return err;
 }
 EXPORT_SYMBOL_GPL(xenbus_map_ring_valloc);
 
-- 
2.20.1