[PATCH 4.18 018/168] mac80211_hwsim: Fix possible Spectre-v1 for hwsim_world_regdom_custom

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jinbum Park <jinb.park7@xxxxxxxxx>

[ Upstream commit 3a2af7cccbbaf2362db9053a946a6084e12bfa73 ]

User controls @idx which to be used as index of hwsim_world_regdom_custom.
So, It can be exploited via Spectre-like attack. (speculative execution)

This kind of attack leaks address of hwsim_world_regdom_custom,
It leads an attacker to bypass security mechanism such as KASLR.

So sanitize @idx before using it to prevent attack.

I leveraged strategy [1] to find and exploit this gadget.

[1] https://github.com/jinb-park/linux-exploit/tree/master/exploit-remaining-spectre-gadget/

Signed-off-by: Jinbum Park <jinb.park7@xxxxxxxxx>
[johannes: unwrap URL]
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/wireless/mac80211_hwsim.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/net/wireless/mac80211_hwsim.c
+++ b/drivers/net/wireless/mac80211_hwsim.c
@@ -33,6 +33,7 @@
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 #include <linux/rhashtable.h>
+#include <linux/nospec.h>
 #include "mac80211_hwsim.h"
 
 #define WARN_QUEUE 100
@@ -3229,6 +3230,9 @@ static int hwsim_new_radio_nl(struct sk_
 			kfree(hwname);
 			return -EINVAL;
 		}
+
+		idx = array_index_nospec(idx,
+					 ARRAY_SIZE(hwsim_world_regdom_custom));
 		param.regd = hwsim_world_regdom_custom[idx];
 	}