Patch "posix-timers: Protect posix clock array access against speculation" has been added to the 4.15-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    posix-timers: Protect posix clock array access against speculation

to the 4.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     posix-timers-protect-posix-clock-array-access-against-speculation.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 19b558db12f9f4e45a22012bae7b4783e62224da Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 15 Feb 2018 17:21:55 +0100
Subject: posix-timers: Protect posix clock array access against speculation

From: Thomas Gleixner <tglx@linutronix.de>

commit 19b558db12f9f4e45a22012bae7b4783e62224da upstream.

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>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1802151718320.1296@nanos.tec.linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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))];
 }


Patches currently in stable-queue which might be from tglx@linutronix.de are

queue-4.15/x86-entry-64-don-t-use-ist-entry-for-bp-stack.patch
queue-4.15/selftests-x86-ptrace_syscall-fix-for-yet-more-glibc-interference.patch
queue-4.15/posix-timers-protect-posix-clock-array-access-against-speculation.patch
queue-4.15/x86-efi-free-efi_pgd-with-free_pages.patch
queue-4.15/x86-vsyscall-64-use-proper-accessor-to-update-p4d-entry.patch
queue-4.15/mm-vmalloc-add-interfaces-to-free-unmapped-page-table.patch
queue-4.15/x86-mm-implement-free-pmd-pte-page-interfaces.patch