From: Paolo Bonzini <pbonzini@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>,
kvm@vger.kernel.org, sean.j.christopherson@intel.com
Cc: syzbot <syzbot+2a7156e11dc199bdbd8a@syzkaller.appspotmail.com>,
bp@alien8.de, hpa@zytor.com, jmattson@google.com,
joro@8bytes.org, linux-kernel@vger.kernel.org, mingo@redhat.com,
syzkaller-bugs@googlegroups.com, tglx@linutronix.de,
wanpengli@tencent.com, x86@kernel.org
Subject: Re: WARNING in kvm_inject_emulated_page_fault
Date: Thu, 4 Jun 2020 15:20:53 +0200 [thread overview]
Message-ID: <c15b3ad0-0062-f106-0746-d018cf33adbb@redhat.com> (raw)
In-Reply-To: <874krrf6ga.fsf@vitty.brq.redhat.com>
On 04/06/20 12:53, Vitaly Kuznetsov wrote:
> Exception we're trying to inject comes from
>
> nested_vmx_get_vmptr()
> kvm_read_guest_virt()
> kvm_read_guest_virt_helper()
> vcpu->arch.walk_mmu->gva_to_gpa()
>
> but it seems it is only set if GVA to GPA convertion fails. In case it
> doesn't, we can still fail kvm_vcpu_read_guest_page() and return
> X86EMUL_IO_NEEDED but nested_vmx_get_vmptr() doesn't case what we return
> and does kvm_inject_emulated_page_fault(). This can happen when VMXON
> parameter is MMIO, for example.
>
> How do fix this? We can either properly exit to userspace for handling
> or, if we decide that handling such requests makes little sense, just
> inject #GP if exception is not set, e.g.
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 9c74a732b08d..a21e2f32f59b 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4635,7 +4635,11 @@ static int nested_vmx_get_vmptr(struct kvm_vcpu *vcpu, gpa_t *vmpointer)
> return 1;
>
> if (kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e)) {
> - kvm_inject_emulated_page_fault(vcpu, &e);
> + if (e.vector == PF_VECTOR)
> + kvm_inject_emulated_page_fault(vcpu, &e);
> + else
> + kvm_inject_gp(vcpu, 0);
> +
> return 1;
> }
>
Yes, this is a plausible fix (with a comment explaining that we are
taking a shortcut). Perhaps a better check would be
r = kvm_read_guest_virt(vcpu, gva, vmpointer, sizeof(*vmpointer), &e);
if (r != X86EMUL_CONTINUE) {
if (r == X86EMUL_PROPAGATE_FAULT) {
kvm_inject_emulated_page_fault(vcpu, &e);
} else {
/* ... */
kvm_inject_gp(vcpu, 0);
}
return 1;
}
Are you going to send a patch?
Paolo
next prev parent reply other threads:[~2020-06-04 13:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-04 8:50 WARNING in kvm_inject_emulated_page_fault syzbot
2020-06-04 10:53 ` Vitaly Kuznetsov
2020-06-04 13:20 ` Paolo Bonzini [this message]
2020-06-04 13:51 ` Vitaly Kuznetsov
2020-06-04 13:09 ` syzbot
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