[PATCH 4.18 14/34] IB/ucm: Fix Spectre v1 vulnerability

Greg Kroah-Hartman
2018-11-09T07:46:59Z

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

commit 0295e39595e1146522f2722715dba7f7fba42217 upstream.

hdr.cmd 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/infiniband/core/ucm.c:1127 ib_ucm_write() warn: potential
spectre issue 'ucm_cmd_table' [r] (local cap)

Fix this by sanitizing hdr.cmd before using it to index
ucm_cmd_table.

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@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/infiniband/core/ucm.c | 3 +++
1 file changed, 3 insertions(+)

--- a/drivers/infiniband/core/ucm.c
+++ b/drivers/infiniband/core/ucm.c
@@ -46,6 +46,8 @@
#include <linux/mutex.h>
#include <linux/slab.h>

+#include <linux/nospec.h>
+
#include <linux/uaccess.h>

#include <rdma/ib.h>
@@ -1123,6 +1125,7 @@ static ssize_t ib_ucm_write(struct file

if (hdr.cmd >= ARRAY_SIZE(ucm_cmd_table))
return -EINVAL;
+ hdr.cmd = array_index_nospec(hdr.cmd, ARRAY_SIZE(ucm_cmd_table));

if (hdr.in + sizeof(hdr) > len)
return -EINVAL;