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Date:   Fri,  1 May 2020 15:21:51 +0200
From:   Greg Kroah-Hartman <>
Cc:     Greg Kroah-Hartman <>,, Juergen Gross <>,
        Wei Liu <>, Sasha Levin <>
Subject: [PATCH 4.4 63/70] xen/xenbus: ensure xenbus_map_ring_valloc() returns proper grant status

From: Juergen Gross <>

[ 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 <>
Reviewed-by: Wei Liu <>
Signed-off-by: Juergen Gross <>
Signed-off-by: Sasha Levin <>
 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 056da6ee1a357..df27cefb2fa35 100644
--- a/drivers/xen/xenbus/xenbus_client.c
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -469,7 +469,14 @@ 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;

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