Messages in this thread Patch in this message | | | Date | Fri, 18 Mar 2016 08:48:06 +0100 (CET) | From | Thomas Gleixner <> | Subject | [PATCH] x86/tsc: Prevent NULL pointer deref in calibrate_delay_is_known() |
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Subject: x86/tsc: Prevent NULL pointer deref in calibrate_delay_is_known() From: Thomas Gleixner <tglx@linutronix.de> Date: Fri, 18 Mar 2016 08:35:29 +0100
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(-)
--- 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;
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