linux-kernel - Re: [RFC KVM 24/27] kvm/isolation: KVM page fault handler

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Date:   Mon, 13 May 2019 09:02:33 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Alexandre Chartre <alexandre.chartre@...cle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        kvm list <kvm@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        jan.setjeeilers@...cle.com, Liran Alon <liran.alon@...cle.com>,
        Jonathan Adams <jwadams@...gle.com>
Subject: Re: [RFC KVM 24/27] kvm/isolation: KVM page fault handler

On Mon, May 13, 2019 at 7:39 AM Alexandre Chartre
<alexandre.chartre@...cle.com> wrote:
>
> The KVM page fault handler handles page fault occurring while using
> the KVM address space by switching to the kernel address space and
> retrying the access (except if the fault occurs while switching
> to the kernel address space). Processing of page faults occurring
> while using the kernel address space is unchanged.
>
> Page fault log is cleared when creating a vm so that page fault
> information doesn't persist when qemu is stopped and restarted.

Are you saying that a page fault will just exit isolation?  This
completely defeats most of the security, right?  Sure, it still helps
with side channels, but not with actual software bugs.