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

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 <[email protected]> know about it.

From: Thomas Gleixner <[email protected]>
Date: Thu, 15 Feb 2018 17:21:55 +0100
Subject: posix-timers: Protect posix clock array access against speculation

From: Thomas Gleixner <[email protected]>

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.

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

@@ -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 [email protected] 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