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@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c
index 8fde44f8cfec2b8e45485dda98f1527d4ece0784..a75f696011d5b2afdb863c6b625222e1af687a2f 100644 (file)
--- 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) {
                /*