On Fri, 01 Jul 2022 22:20:45 +0530 Jue Wang <juew@xxxxxxxxxx> wrote
> Fix an access to vcpu->arch.apic when KVM_X86_SETUP_MCE is called
> without KVM_CREATE_IRQCHIP called or KVM_CAP_SPLIT_IRQCHIP is
> enabled.
>
> Fixes: 4b903561ec49 ("KVM: x86: Add Corrected Machine Check Interrupt (CMCI) emulation to lapic.")
> Signed-off-by: Jue Wang <juew@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4322a1365f74..d81020dd0fea 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4820,8 +4820,9 @@ static int kvm_vcpu_ioctl_x86_setup_mce(struct kvm_vcpu *vcpu,
> if (mcg_cap & MCG_CMCI_P)
> vcpu->arch.mci_ctl2_banks[bank] = 0;
> }
> - vcpu->arch.apic->nr_lvt_entries =
> - KVM_APIC_MAX_NR_LVT_ENTRIES - !(mcg_cap & MCG_CMCI_P);
> + if (vcpu->arch.apic)
> + vcpu->arch.apic->nr_lvt_entries =
> + KVM_APIC_MAX_NR_LVT_ENTRIES - !(mcg_cap & MCG_CMCI_P);
>
> static_call(kvm_x86_setup_mce)(vcpu);
> out:
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>
>
Hello Jue,
There is a syzkaller bug regarding null ptr dereference which is caused by
vcpu->arch.apic being NULL, first reported on 27th June. You might want to
add it's reported-by line so that it can be marked as fixed.
Link: https://syzkaller.appspot.com/bug?id=10b9b238e087a6c9bef2cc48bee2375f58fabbfc
I was looking at this bug too and fixed it (i.e. reproducer won't crash)
using lapic_in_kernel(vcpu) as a condition instead of null ptr check on
vcpu->arch.apic, as it makes more sense to the code reader (the lapic is
not there since during kvm_arch_vcpu_create(), it isn't created due to
irqchip_in_kernel() check being false).
May I suggest that lapic_in_kernel(vcpu) be used instead of the null ptr
check?
Thanks,
Siddh
