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