[PATCH 4.16 51/72] atm: zatm: Fix potential Spectre v1

From: Greg Kroah-Hartman
Date: Mon May 14 2018 - 03:00:00 EST

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


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

commit 2be147f7459db5bbf292e0a6f135037b55e20b39 upstream.

pool 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/atm/zatm.c:1462 zatm_ioctl() warn: potential spectre issue
'zatm_dev->pool_info' (local cap)

Fix this by sanitizing pool before using it to index

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/atm/zatm.c | 3 +++
1 file changed, 3 insertions(+)

--- a/drivers/atm/zatm.c
+++ b/drivers/atm/zatm.c
@@ -28,6 +28,7 @@
#include <asm/io.h>
#include <linux/atomic.h>
#include <linux/uaccess.h>
+#include <linux/nospec.h>

#include "uPD98401.h"
#include "uPD98402.h"
@@ -1458,6 +1459,8 @@ static int zatm_ioctl(struct atm_dev *de
return -EFAULT;
if (pool < 0 || pool > ZATM_LAST_POOL)
return -EINVAL;
+ pool = array_index_nospec(pool,
spin_lock_irqsave(&zatm_dev->lock, flags);
info = zatm_dev->pool_info[pool];
if (cmd == ZATM_GETPOOLZ) {