linux-kernel - Re: [PATCH] kvm: fix page struct leak in handle

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Date:   Wed, 25 Jan 2017 04:52:06 -0500 (EST)
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        dvyukov@...gle.com
Subject: Re: [PATCH] kvm: fix page struct leak in handle_vmon



----- Original Message -----
> From: "David Hildenbrand" <david@...hat.com>
> To: "Paolo Bonzini" <pbonzini@...hat.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
> Cc: dvyukov@...gle.com
> Sent: Wednesday, January 25, 2017 10:31:13 AM
> Subject: Re: [PATCH] kvm: fix page struct leak in handle_vmon
> 
> Am 24.01.2017 um 11:56 schrieb Paolo Bonzini:
> > handle_vmon gets a reference on VMXON region page,
> > but does not release it. Release the reference.
> > 
> > Found by syzkaller; based on a patch by Dmitry.
> > 
> > Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > ---
> >  arch/x86/kvm/vmx.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index 42cc3d6f4d20..0f7345035210 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -7085,13 +7085,18 @@ static int nested_vmx_check_vmptr(struct kvm_vcpu
> > *vcpu, int exit_reason,
> >  		}
> >  
> >  		page = nested_get_page(vcpu, vmptr);
> > -		if (page == NULL ||
> > -		    *(u32 *)kmap(page) != VMCS12_REVISION) {
> > +		if (page == NULL) {
> >  			nested_vmx_failInvalid(vcpu);
> > +			return kvm_skip_emulated_instruction(vcpu);
> > +		}
> > +		if (*(u32 *)kmap(page) != VMCS12_REVISION) {
> 
> shouldn't we also check if kmap even returned a valid pointer before
> dereferencing it?

I don't think kmap can fail (page_address can)?

Paolo

> >  			kunmap(page);
> > +			nested_release_page_clean(page);
> > +			nested_vmx_failInvalid(vcpu);
> >  			return kvm_skip_emulated_instruction(vcpu);
> >  		}
> >  		kunmap(page);
> > +		nested_release_page_clean(page);
> >  		vmx->nested.vmxon_ptr = vmptr;
> >  		break;
> >  	case EXIT_REASON_VMCLEAR:
> > 
> 
> --
> 
> David
>