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>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c94895bc5a2c14dc05117a7050fb9b3964db0357..5f37ef9f6cd5030a495e868e324c887d22b04b4b 100644 (file)
--- 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