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Subject[PATCH 3.2 140/153] posix-timers: Protect posix clock array access against speculation
3.2.102-rc1 review patch.  If anyone has any objections, please let me know.

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

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: 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
[bwh: Backported to 3.2:
- Move the test of the clock_getres field below the lookup using
array_index_nospec()
- Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -47,6 +47,7 @@
#include <linux/wait.h>
#include <linux/workqueue.h>
#include <linux/export.h>
+#include <linux/nospec.h>

/*
* Management arrays for POSIX timers. Timers are kept in slab memory
@@ -520,13 +521,21 @@ static void release_posix_timer(struct k

static struct k_clock *clockid_to_kclock(const clockid_t id)
{
- if (id < 0)
+ clockid_t idx = id;
+ struct k_clock *kc;
+
+ if (id < 0) {
return (id & CLOCKFD_MASK) == CLOCKFD ?
&clock_posix_dynamic : &clock_posix_cpu;
+ }
+
+ if (id >= ARRAY_SIZE(posix_clocks))
+ return NULL;

- if (id >= MAX_CLOCKS || !posix_clocks[id].clock_getres)
+ kc = &posix_clocks[array_index_nospec(idx, ARRAY_SIZE(posix_clocks))];
+ if (!kc->clock_getres)
return NULL;
- return &posix_clocks[id];
+ return kc;
}

static int common_timer_create(struct k_itimer *new_timer)
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