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Subject[PATCH 3.16 184/305] drivers/misc/sgi-gru: fix Spectre v1 vulnerability
3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

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

From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>

commit fee05f455ceb5c670cbe48e2f9454ebc4a388554 upstream.

req.gid 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:

vers/misc/sgi-gru/grukdump.c:200 gru_dump_chiplet_request() warn:
potential spectre issue 'gru_base' [w]

Fix this by sanitizing req.gid before calling macro GID_TO_GRU, which
uses it to index gru_base.

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

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/misc/sgi-gru/grukdump.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/drivers/misc/sgi-gru/grukdump.c
+++ b/drivers/misc/sgi-gru/grukdump.c
@@ -27,6 +27,9 @@
#include <linux/delay.h>
#include <linux/bitops.h>
#include <asm/uv/uv_hub.h>
+
+#include <linux/nospec.h>
+
#include "gru.h"
#include "grutables.h"
#include "gruhandles.h"
@@ -198,6 +201,7 @@ int gru_dump_chiplet_request(unsigned lo
/* Currently, only dump by gid is implemented */
if (req.gid >= gru_max_gids || req.gid < 0)
return -EINVAL;
+ req.gid = array_index_nospec(req.gid, gru_max_gids);

gru = GID_TO_GRU(req.gid);
ubuf = req.buf;
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