linux-kernel - [PATCH] posix-timers: Protect posix clock array access against speculation

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Date:   Thu, 15 Feb 2018 14:27:30 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
cc:     Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: [PATCH] posix-timers: Protect posix clock array access against
 speculation

The (clock) id argument of clockid_to_kclock() comes straight from user
space via various syscalls and is used as index into the posix_clocks
array.

Protect it against spectre v1 array out of bounds speculation.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org
---
 kernel/time/posix-timers.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -50,6 +50,7 @@
 #include <linux/export.h>
 #include <linux/hashtable.h>
 #include <linux/compat.h>
+#include <linux/nospec.h>
 
 #include "timekeeping.h"
 #include "posix-timers.h"
@@ -1346,11 +1347,14 @@ static const struct k_clock * const posi
 
 static const struct k_clock *clockid_to_kclock(const clockid_t id)
 {
+	clockid_t idx = id;
+
 	if (id < 0)
 		return (id & CLOCKFD_MASK) == CLOCKFD ?
 			&clock_posix_dynamic : &clock_posix_cpu;
 
 	if (id >= ARRAY_SIZE(posix_clocks) || !posix_clocks[id])
 		return NULL;
-	return posix_clocks[id];
+
+	return posix_clocks[array_index_nospec(idx, ARRAY_SIZE(posix_clocks))];
 }