[PATCH] IB/ucm: Fix Spectre v1 vulnerability

From: Gustavo A. R. Silva
Date: Tue Oct 16 2018 - 10:32:47 EST

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

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

diff --git a/drivers/infiniband/core/ucm.c b/drivers/infiniband/core/ucm.c
index faa9e61..73332b9 100644
--- 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>
@@ -1120,6 +1122,7 @@ static ssize_t ib_ucm_write(struct file *filp, const char __user *buf,

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;