linux-kernel - [PATCH AUTOSEL 5.15 49/98] dm ioctl: prevent potential spectre v1 gadget

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Date:   Fri,  1 Apr 2022 10:36:53 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Jordy Zomer <jordy@...dyzomer.github.io>,
        Jordy Zomer <jordy@...ing.systems>,
        Mike Snitzer <snitzer@...hat.com>,
        Sasha Levin <sashal@...nel.org>, agk@...hat.com,
        snitzer@...nel.org, dm-devel@...hat.com
Subject: [PATCH AUTOSEL 5.15 49/98] dm ioctl: prevent potential spectre v1 gadget

From: Jordy Zomer <jordy@...dyzomer.github.io>

[ Upstream commit cd9c88da171a62c4b0f1c70e50c75845969fbc18 ]

It appears like cmd could be a Spectre v1 gadget as it's supplied by a
user and used as an array index. Prevent the contents of kernel memory
from being leaked to userspace via speculative execution by using
array_index_nospec.

Signed-off-by: Jordy Zomer <jordy@...ing.systems>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/md/dm-ioctl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 21fe8652b095..901abd6dea41 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -18,6 +18,7 @@
 #include <linux/dm-ioctl.h>
 #include <linux/hdreg.h>
 #include <linux/compat.h>
+#include <linux/nospec.h>
 
 #include <linux/uaccess.h>
 #include <linux/ima.h>
@@ -1788,6 +1789,7 @@ static ioctl_fn lookup_ioctl(unsigned int cmd, int *ioctl_flags)
 	if (unlikely(cmd >= ARRAY_SIZE(_ioctls)))
 		return NULL;
 
+	cmd = array_index_nospec(cmd, ARRAY_SIZE(_ioctls));
 	*ioctl_flags = _ioctls[cmd].flags;
 	return _ioctls[cmd].fn;
 }
-- 
2.34.1