Messages in this thread | | | Subject | Re: [syzbot] WARNING in static_key_slow_try_dec (2) | From | Tetsuo Handa <> | Date | Sun, 10 Oct 2021 14:34:18 +0900 |
| |
Hello.
Commit 4547700a4d190ac4 ("KVM: x86: Consolidate APIC base RESET initialization code") changed the location to set MSR_IA32_APICBASE_ENABLE flag. And syzbot is reporting underflow bug due to too late initialization of vcpu->arch.apic_base member. We need to make sure that vcpu->arch.apic_base is initialized before kvm_free_lapic() is called.
kvm_vm_ioctl() { kvm_vm_ioctl_create_vcpu() { kvm_arch_vcpu_create() { if (something_went_wrong) goto fail_free_lapic; /* vcpu->arch.apic_base is initialized when something_went_wrong is false. */ kvm_vcpu_reset() { kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event) { vcpu->arch.apic_base = APIC_DEFAULT_PHYS_BASE | MSR_IA32_APICBASE_ENABLE; } } return 0; fail_free_lapic: kvm_free_lapic() { /* vcpu->arch.apic_base is not yet initialized when something_went_wrong is true. */ if (!(vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE)) static_branch_slow_dec_deferred(&apic_hw_disabled); // <= underflow bug. } return r; } } }
| |