From 5d728a4ecab107668f241c6d2a10cc9380830c25 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Fri, 20 Apr 2018 14:29:51 +0200
Subject: [PATCH] sched/core: Fix possible Spectre-v1 indexing for
 sched_prio_to_weight[]

commit 7281c8dec8a87685cb54d503d8cceef5a0fc2fdd upstream.

> kernel/sched/core.c:6921 cpu_weight_nice_write_s64() warn: potential spectre issue 'sched_prio_to_weight'

Userspace controls @nice, so sanitize the value before using it to
index an array.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/sched/core.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c94895bc5a2c..5f37ef9f6cd5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -23,6 +23,7 @@
 #include <linux/mmu_context.h>
 #include <linux/module.h>
 #include <linux/nmi.h>
+#include <linux/nospec.h>
 #include <linux/prefetch.h>
 #include <linux/profile.h>
 #include <linux/security.h>
@@ -6873,11 +6874,15 @@ static int cpu_weight_nice_write_s64(struct cgroup_subsys_state *css,
 				     struct cftype *cft, s64 nice)
 {
 	unsigned long weight;
+	int idx;
 
 	if (nice < MIN_NICE || nice > MAX_NICE)
 		return -ERANGE;
 
-	weight = sched_prio_to_weight[NICE_TO_PRIO(nice) - MAX_RT_PRIO];
+	idx = NICE_TO_PRIO(nice) - MAX_RT_PRIO;
+	idx = array_index_nospec(idx, 40);
+	weight = sched_prio_to_weight[idx];
+
 	return sched_group_set_shares(css_tg(css), scale_load(weight));
 }
 #endif
-- 
2.43.0