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From: Thomas Gleixner <tglx@linutronix.de>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	David Woodhouse <dwmw@amazon.co.uk>,
	Greg KH <gregkh@linuxfoundation.org>,
	Peter Zijlstra <peterz@infradead.org>
Subject: [PATCH V2] posix-timers: Protect posix clock array access against speculation
Date: Thu, 15 Feb 2018 17:21:55 +0100 (CET)
Message-ID: <alpine.DEB.2.21.1802151718320.1296@nanos.tec.linutronix.de> (raw)
In-Reply-To: <alpine.DEB.2.21.1802151550330.1296@nanos.tec.linutronix.de>

The clockid 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. Remove the
redundant check for !posix_clock[id] as this is another source for
speculation and does not provide any advantage over the return
posix_clock[id] path which returns NULL in that case anyway.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
---

V2: Remove the redundant !posix_clocks[id] check.

 kernel/time/posix-timers.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- 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 +1347,15 @@ static const struct k_clock * const posi
 
 static const struct k_clock *clockid_to_kclock(const clockid_t id)
 {
-	if (id < 0)
+	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])
+	if (id >= ARRAY_SIZE(posix_clocks))
 		return NULL;
-	return posix_clocks[id];
+
+	return posix_clocks[array_index_nospec(idx, ARRAY_SIZE(posix_clocks))];
 }

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-15 13:27 [PATCH] " Thomas Gleixner
2018-02-15 14:05 ` Rasmus Villemoes
2018-02-15 14:39   ` Dan Williams
2018-02-15 14:53     ` Thomas Gleixner
2018-02-15 16:21       ` Thomas Gleixner [this message]
2018-02-15 17:01         ` [PATCH V2] " Peter Zijlstra
2018-03-07 18:13           ` Dan Williams
2018-03-22 11:34         ` [tip:timers/urgent] " tip-bot for Thomas Gleixner
2018-02-15 19:52     ` [PATCH] linux/nospec.h: allow index argument to have const-qualified type Rasmus Villemoes
2018-02-15 20:59       ` Linus Torvalds
2018-02-15 21:56         ` Dan Williams
2018-02-15 22:03           ` Linus Torvalds
2018-02-15 22:08             ` Dan Williams

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