Commit-ID: 31f8a651fc5784a9e6f482be5ef0dd111a535e88
Gitweb: http://git.kernel.org/tip/31f8a651fc5784a9e6f482be5ef0dd111a535e88
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Thu, 1 Dec 2016 13:26:58 +0100
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Thu, 1 Dec 2016 14:40:52 +0100
x86/tsc: Validate cpumask pointer before accessing it
0-day testing encountered a NULL pointer dereference in a cpumask access
from tsc_store_and_check_tsc_adjust().
This happens when the function is called on the boot CPU and the topology
masks are not yet available due to CPUMASK_OFFSTACK=y.
Add a NULL pointer check for the mask pointer. If NULL it's safe to assume
that the CPU is the boot CPU and the first one in the package.
Fixes: 8b223bc7abe0 ("x86/tsc: Store and check TSC ADJUST MSR")
Reported-by: kernel test robot <xiaolong.ye@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/x86/kernel/tsc_sync.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c
index 8fde44f..a75f696 100644
--- a/arch/x86/kernel/tsc_sync.c
+++ b/arch/x86/kernel/tsc_sync.c
@@ -84,6 +84,7 @@ bool tsc_store_and_check_tsc_adjust(void)
{
struct tsc_adjust *ref, *cur = this_cpu_ptr(&tsc_adjust);
unsigned int refcpu, cpu = smp_processor_id();
+ struct cpumask *mask;
s64 bootval;
if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
@@ -98,9 +99,11 @@ bool tsc_store_and_check_tsc_adjust(void)
* Check whether this CPU is the first in a package to come up. In
* this case do not check the boot value against another package
* because the package might have been physically hotplugged, where
- * TSC_ADJUST is expected to be different.
+ * TSC_ADJUST is expected to be different. When called on the boot
+ * CPU topology_core_cpumask() might not be available yet.
*/
- refcpu = cpumask_any_but(topology_core_cpumask(cpu), cpu);
+ mask = topology_core_cpumask(cpu);
+ refcpu = mask ? cpumask_any_but(mask, cpu) : nr_cpu_ids;
if (refcpu >= nr_cpu_ids) {
/*
--
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