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From:   Jinpu Wang <jinpuwang@gmail.com>
Date:   Wed, 13 Nov 2019 14:00:44 +0100
Message-ID: <CAD9gYJ+9sDYh+8RkbaaRrMEbJ1EJrkMdJFCa6HVPUE4_FA13ag@mail.gmail.com>
Subject: Re: [FYI PATCH 0/7] Mitigation for CVE-2018-12207
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        "KVM-ML (kvm@vger.kernel.org)" <kvm@vger.kernel.org>
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Paolo Bonzini <pbonzini@redhat.com> =E4=BA=8E2019=E5=B9=B411=E6=9C=8812=E6=
=97=A5=E5=91=A8=E4=BA=8C =E4=B8=8B=E5=8D=8810:23=E5=86=99=E9=81=93=EF=BC=9A
>
> CVE-2018-12207 is a microarchitectural implementation issue
> that could allow an unprivileged local attacker to cause system wide
> denial-of-service condition.
>
> Privileged software may change the page size (ex. 4KB, 2MB, 1GB) in the
> paging structures, without following such paging structure changes with
> invalidation of the TLB entries corresponding to the changed pages. In
> this case, the attacker could invoke instruction fetch, which will result
> in the processor hitting multiple TLB entries, reporting a machine check
> error exception, and ultimately hanging the system.
>
> The attached patches mitigate the vulnerability by making huge pages
> non-executable. The processor will not be able to execute an instruction
> residing in a large page (ie. 2MB, 1GB, etc.) without causing a trap into
> the host kernel/hypervisor; KVM will then break the large page into 4KB
> pages and gives executable permission to 4KB pages.
>
> Thanks to everyone that was involved in the development of these patches,
> especially Junaid Shahid, who provided the first version of the code,
> and Thomas Gleixner.
>
> Paolo
Hi Paolo, hi list,

Thanks for info, do we need qemu patch for full mitigation?
Debian mentioned:
https://linuxsecurity.com/advisories/debian/debian-dsa-4566-1-qemu-security=
-update-17-10-10
"
    A qemu update adding support for the PSCHANGE_MC_NO feature, which
    allows to disable iTLB Multihit mitigations in nested hypervisors
    will be provided via DSA 4566-1.

"
But It's not yet available  publicly.
About the performance hit, do you know any number? probably the answer
is workload dependent.

Regards,
Jack Wang