The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 7a22e03b0c02988e91003c505b34d752a51de344 Gitweb: https://git.kernel.org/tip/7a22e03b0c02988e91003c505b34d752a51de344 Author: Sean Christopherson sean.j.christopherson@intel.com AuthorDate: Tue, 01 Oct 2019 13:50:19 -07:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Tue, 15 Oct 2019 10:57:09 +02:00

x86/apic/x2apic: Fix a NULL pointer deref when handling a dying cpu

Check that the per-cpu cluster mask pointer has been set prior to clearing a dying cpu's bit. The per-cpu pointer is not set until the target cpu reaches smp_callin() during CPUHP_BRINGUP_CPU, whereas the teardown function, x2apic_dead_cpu(), is associated with the earlier CPUHP_X2APIC_PREPARE. If an error occurs before the cpu is awakened, e.g. if do_boot_cpu() itself fails, x2apic_dead_cpu() will dereference the NULL pointer and cause a panic.

smpboot: do_boot_cpu failed(-22) to wakeup CPU#1 BUG: kernel NULL pointer dereference, address: 0000000000000008 RIP: 0010:x2apic_dead_cpu+0x1a/0x30 Call Trace: cpuhp_invoke_callback+0x9a/0x580 _cpu_up+0x10d/0x140 do_cpu_up+0x69/0xb0 smp_init+0x63/0xa9 kernel_init_freeable+0xd7/0x229 ? rest_init+0xa0/0xa0 kernel_init+0xa/0x100 ret_from_fork+0x35/0x40

Fixes: 023a611748fd5 ("x86/apic/x2apic: Simplify cluster management") Signed-off-by: Sean Christopherson sean.j.christopherson@intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20191001205019.5789-1-sean.j.christopherson@intel....

--- arch/x86/kernel/apic/x2apic_cluster.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c index 45e92cb..b0889c4 100644 --- a/arch/x86/kernel/apic/x2apic_cluster.c +++ b/arch/x86/kernel/apic/x2apic_cluster.c @@ -156,7 +156,8 @@ static int x2apic_dead_cpu(unsigned int dead_cpu) { struct cluster_mask *cmsk = per_cpu(cluster_masks, dead_cpu);

- cpumask_clear_cpu(dead_cpu, &cmsk->mask); + if (cmsk) + cpumask_clear_cpu(dead_cpu, &cmsk->mask); free_cpumask_var(per_cpu(ipi_mask, dead_cpu)); return 0; }