[PATCH] IB/core: Add mitigation for Spectre V1

[Tony Luck]

Some processors may mispredict an array bounds check and
speculatively access memory that they should not. With
a user supplied array index we like to play things safe
by masking the value with the array size before it is
used as an index.

Signed-off-by: Tony Luck <tony.l...@intel.com>
---

[I don't have h/w, so just compile tested]

 drivers/infiniband/core/user_mad.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/infiniband/core/user_mad.c 
b/drivers/infiniband/core/user_mad.c
index 9f8a48016b41..fdce254e4f65 100644
--- a/drivers/infiniband/core/user_mad.c
+++ b/drivers/infiniband/core/user_mad.c
@@ -49,6 +49,7 @@
 #include <linux/sched.h>
 #include <linux/semaphore.h>
 #include <linux/slab.h>
+#include <linux/nospec.h>
 
 #include <linux/uaccess.h>
 
@@ -888,6 +889,7 @@ static int ib_umad_unreg_agent(struct ib_umad_file *file, 
u32 __user *arg)
        mutex_lock(&file->port->file_mutex);
        mutex_lock(&file->mutex);
 
+       id = array_index_nospec(id, IB_UMAD_MAX_AGENTS);
        if (id >= IB_UMAD_MAX_AGENTS || !__get_agent(file, id)) {
                ret = -EINVAL;
                goto out;
-- 
2.20.1