IB/ucm: Fix Spectre v1 vulnerability

GustavoARSilva · dledford · commit 0295e39595e1 · 2018-10-16T11:32:40.000-04:00
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>
diff --git 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;
