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posix-timers: Protect posix clock array access against speculation

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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
This commit is contained in:
Thomas Gleixner 2018-02-15 17:21:55 +01:00
parent 1b5f3ba415
commit 19b558db12
1 changed files with 8 additions and 3 deletions
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11
kernel/time/posix-timers.c
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@ -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 posix_clocks[] = {
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))];
}