linux-kernel - Re: [RFC PATCH V3 3/4] KVM: X86: Alloc role.pae

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: <683974e7-5801-e289-8fa4-c8a8d21ec1b2@redhat.com>
Date:   Thu, 14 Apr 2022 11:08:45 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH V3 3/4] KVM: X86: Alloc role.pae_root shadow page

On 4/14/22 11:07, Lai Jiangshan wrote:
>> I don't think this will work for shadow paging.  CR3 only has to be 32-byte aligned
>> for PAE paging.  Unless I'm missing something subtle in the code, KVM will incorrectly
>> reuse a pae_root if the guest puts multiple PAE CR3s on a single page because KVM's
>> gfn calculation will drop bits 11:5.
> 
> I forgot about it.


Isn't the pae_root always rebuilt by

         if (!tdp_enabled && memcmp(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs)))
                 kvm_mmu_free_roots(vcpu->kvm, mmu, KVM_MMU_ROOT_CURRENT);

in load_pdptrs?  I think reuse cannot happen.

Paolo