[PATCH 4.4 49/56] atm: zatm: Fix potential Spectre v1

From: Greg Kroah-Hartman
Date: Mon May 14 2018 - 03:38:08 EST


4.4-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
zatm_dev->pool_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/atm/zatm.c | 3 +++
1 file changed, 3 insertions(+)

--- a/drivers/atm/zatm.c
+++ b/drivers/atm/zatm.c
@@ -23,6 +23,7 @@
#include <linux/bitops.h>
#include <linux/wait.h>
#include <linux/slab.h>
+#include <linux/nospec.h>
#include <asm/byteorder.h>
#include <asm/string.h>
#include <asm/io.h>
@@ -1456,6 +1457,8 @@ static int zatm_ioctl(struct atm_dev *de
return -EFAULT;
if (pool < 0 || pool > ZATM_LAST_POOL)
return -EINVAL;
+ pool = array_index_nospec(pool,
+ ZATM_LAST_POOL + 1);
spin_lock_irqsave(&zatm_dev->lock, flags);
info = zatm_dev->pool_info[pool];
if (cmd == ZATM_GETPOOLZ) {