sched/core: Fix possible Spectre-v1 indexing for sched_prio_to_weight[]

> 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>

1 files changed, 6 insertions, 1 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ffde9eebc846..092f7c4de903 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8,6 +8,7 @@
 #include "sched.h"
 
 #include <linux/kthread.h>
+#include <linux/nospec.h>
 
 #include <asm/switch_to.h>
 #include <asm/tlb.h>
@@ -6923,11 +6924,15 @@ 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