linux-kernel - Re: [PATCH] KVM: nVMX: Prevent vmlaunch with EPTP pointing outside assigned memory area

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZJ72omPGZcdjjWbo@google.com>
Date:   Fri, 30 Jun 2023 08:37:06 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yuan Yao <yuan.yao@...ux.intel.com>
Cc:     Yan Zhao <yan.y.zhao@...el.com>,
        Reima Ishii <ishiir@...cc.u-tokyo.ac.jp>,
        shina@....u-tokyo.ac.jp, Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, yuan.yao@...el.com
Subject: Re: [PATCH] KVM: nVMX: Prevent vmlaunch with EPTP pointing outside
 assigned memory area

On Fri, Jun 30, 2023, Yuan Yao wrote:
> On Thu, Jun 29, 2023 at 01:30:31PM -0700, Sean Christopherson wrote:
> > @@ -3834,8 +3822,8 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
> >  			if (!(pdptrs[i] & PT_PRESENT_MASK))
> >  				continue;
> >
> > -			if (mmu_check_root(vcpu, pdptrs[i] >> PAGE_SHIFT))
> > -				return 1;
> > +			if (kvm_vcpu_is_visible_gfn(vcpu, pdptrs[i] >> PAGE_SHIFT))
> > +				pdptrs[i] = 0;
> 
> Hi Sean,
> 
> Should this be "!kvm_vcpu_is_visible_gfn(vcpu, pdptrs[i] >> PAGE_SHIFT)" and

Yep, typo that inverted the check.  Thanks for saving me some debug time!

> turn the pae_root[i] to dummy root yet ?

No, zeroing the PDPTR is sufficient.  Unlike CR3, which is always "present", PDPTRs
have a present bit and so KVM can communicate to hardware that the entry isn't
valid simply by clearing the PDPTPR.