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posix-timers: Protect posix clock array access against speculation

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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.

Change-Id: Id7011ec27ea4532d573425ce467f0c815fa20a07
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>
This commit is contained in:
Thomas Gleixner 2018-02-15 17:21:55 +01:00 committed by syphyr
parent 12c59ed87c
commit c255262f5e
1 changed files with 12 additions and 3 deletions
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15
kernel/posix-timers.c
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@ -48,6 +48,7 @@
#include <linux/workqueue.h>
#include <linux/export.h>
#include <linux/hashtable.h>
#include <linux/nospec.h>
/*
* Management arrays for POSIX timers. Timers are now kept in static hash table
@ -578,13 +579,21 @@ static void release_posix_timer(struct k_itimer *tmr, int it_id_set)
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 >= MAX_CLOCKS || !posix_clocks[id].clock_getres)
if (id >= ARRAY_SIZE(posix_clocks))
return NULL;
return &posix_clocks[id];
kc = &posix_clocks[array_index_nospec(idx, ARRAY_SIZE(posix_clocks))];
if (!kc->clock_getres)
return NULL;
return kc;
}
static int common_timer_create(struct k_itimer *new_timer)