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SubjectRe: [PATCH] KVM: x86: Initialize tdp_level during vCPU creation
On Wed, May 27, 2020 at 06:17:57PM +0200, Paolo Bonzini wrote:
> On 27/05/20 10:54, Sean Christopherson wrote:
> > Initialize vcpu->arch.tdp_level during vCPU creation to avoid consuming
> > garbage if userspace calls KVM_RUN without first calling KVM_SET_CPUID.
> >
> > Fixes: e93fd3b3e89e9 ("KVM: x86/mmu: Capture TDP level when updating CPUID")
> > Reported-by: syzbot+904752567107eefb728c@syzkaller.appspotmail.com
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > ---
> > arch/x86/kvm/x86.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index b226fb8abe41b..01a6304056197 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -9414,6 +9414,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> > fx_init(vcpu);
> >
> > vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
> > + vcpu->arch.tdp_level = kvm_x86_ops.get_tdp_level(vcpu);
> >
> > vcpu->arch.pat = MSR_IA32_CR_PAT_DEFAULT;
>
> Queued, it is probably a good idea to add a selftests testcase for this
> (it's even okay if it doesn't use the whole selftests infrastructure and
> invokes KVM_CREATE_VM/KVM_CREATE_VCPU/KVM_RUN manually).

Ya. syzbot is hitting a #GP due to NULL pointer during debugfs on the exact
same sequence. I haven't been able to reproduce that one (have yet to try
syzbot's exact config), but it's another example of a "dumb" test hitting
meaningful bugs.

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