[PATCH 3.16 263/366] sched/autogroup: Fix possible Spectre-v1 indexing for sched_prio_to_weight[]

Ben Hutchings
2018-10-14T23:12:02Z

From: Peter Zijlstra <peterz@infradead.org>

commit 354d7793070611b4df5a79fbb0f12752d0ed0cc5 upstream.

> kernel/sched/autogroup.c:230 proc_sched_autogroup_set_nice() warn: potential spectre issue 'sched_prio_to_weight'

Userspace controls @nice, sanitize the array index.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.16: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
kernel/sched/auto_group.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -8,6 +8,7 @@
#include <linux/utsname.h>
#include <linux/security.h>
#include <linux/export.h>
+#include <linux/nospec.h>

unsigned int __read_mostly sysctl_sched_autogroup_enabled = 1;
static struct autogroup autogroup_default;
@@ -198,7 +199,7 @@ int proc_sched_autogroup_set_nice(struct
static unsigned long next = INITIAL_JIFFIES;
struct autogroup *ag;
unsigned long shares;
- int err;
+ int err, idx;

if (nice < MIN_NICE || nice > MAX_NICE)
return -EINVAL;
@@ -216,7 +217,9 @@ int proc_sched_autogroup_set_nice(struct

next = HZ / 10 + jiffies;
ag = autogroup_task_get(p);
- shares = scale_load(prio_to_weight[nice + 20]);
+
+ idx = array_index_nospec(nice + 20, 40);
+ shares = scale_load(prio_to_weight[idx]);

down_write(&ag->lock);
err = sched_group_set_shares(ag->tg, shares);