From 6b1292e2e61669457398e3b55e46490e7efca5f0 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 18 Mar 2016 08:35:29 +0100
Subject: [PATCH] x86/tsc: Prevent NULL pointer deref in
calibrate_delay_is_known()
The topology_core_cpumask is used to find a neighbour cpu in
calibrate_delay_is_known(). It might not be allocated at the first invocation
of that function on the boot cpu, when CONFIG_CPUMASK_OFFSTACK is set.
The mask is allocated later in native_smp_prepare_cpus. As a consequence the
underlying find_next_bit() call dereferences a NULL pointer.
Add a proper check to prevent this.
Reported-by: Richard W.M. Jones <rjones@redhat.com>
Fixes: c25323c07345 "x86/tsc: Use topology functions"
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Boyer <jwboyer@fedoraproject.org>
---
arch/x86/kernel/tsc.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 56380440d862..99b5e0809ead 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1306,11 +1306,15 @@ void __init tsc_init(void)
unsigned long calibrate_delay_is_known(void)
{
int sibling, cpu = smp_processor_id();
+ struct cpumask *mask = topology_core_cpumask(cpu);
if (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC))
return 0;
- sibling = cpumask_any_but(topology_core_cpumask(cpu), cpu);
+ if (!mask)
+ return 0;
+
+ sibling = cpumask_any_but(mask, cpu);
if (sibling < nr_cpu_ids)
return cpu_data(sibling).loops_per_jiffy;
return 0;
--
2.5.0