[PATCH 4.4 24/31] net: cxgb3_main: fix potential Spectre v1

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>

commit 676bcfece19f83621e905aa55b5ed2d45cc4f2d3 upstream.

t.qset_idx can be indirectly controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

drivers/net/ethernet/chelsio/cxgb3/cxgb3_main.c:2286 cxgb_extension_ioctl()
warn: potential spectre issue 'adapter->msix_info'

Fix this by sanitizing t.qset_idx before using it to index
adapter->msix_info

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/net/ethernet/chelsio/cxgb3/cxgb3_main.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/net/ethernet/chelsio/cxgb3/cxgb3_main.c
+++ b/drivers/net/ethernet/chelsio/cxgb3/cxgb3_main.c
@@ -50,6 +50,7 @@
 #include <linux/stringify.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/nospec.h>
 #include <asm/uaccess.h>
 
 #include "common.h"
@@ -2256,6 +2257,7 @@ static int cxgb_extension_ioctl(struct n
 
 		if (t.qset_idx >= nqsets)
 			return -EINVAL;
+		t.qset_idx = array_index_nospec(t.qset_idx, nqsets);
 
 		q = &adapter->params.sge.qset[q1 + t.qset_idx];
 		t.rspq_size = q->rspq_size;