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Message-ID: <CAPcxDJ51EQwTZzNOzckRGXgE9s6X+rpDWFxvb8JZpAQQVjm1iQ@mail.gmail.com>
Date: Wed, 6 Jul 2022 08:07:29 -0700
From: Jue Wang <juew@...gle.com>
To: Siddh Raman Pant <code@...dh.me>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Jim Mattson <jmattson@...gle.com>,
Xiaoyao Li <xiaoyao.li@...el.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Joerg Roedel <joro@...tes.org>,
David Matlack <dmatlack@...gle.com>,
Tony Luck <tony.luck@...el.com>, kvm <kvm@...r.kernel.org>,
Jiaqi Yan <jiaqiyan@...gle.com>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] KVM: x86: Fix access to vcpu->arch.apic when the
irqchip is not in kernel
Hi Siddh,
Thanks for the note.
I've sent out an updated v2 patch:
https://lore.kernel.org/kvm/20220706145957.32156-2-juew@google.com/T/#u
Thanks,
-Jue
On Sun, Jul 3, 2022 at 7:44 AM Siddh Raman Pant <code@...dh.me> wrote:
>
> On Fri, 01 Jul 2022 22:20:45 +0530 Jue Wang <juew@...gle.com> 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@...gle.com>
> > ---
> > 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
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