From 6b1292e2e61669457398e3b55e46490e7efca5f0 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner 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 Fixes: c25323c07345 "x86/tsc: Use topology functions" Signed-off-by: Thomas Gleixner Cc: Josh Boyer --- 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