linux-kernel - Re: [PATCH V7 0/10] KVM: X86: Introducing ROE Protection Kernel Hardening

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Date:   Thu, 13 Dec 2018 13:36:27 +0000
From:   "Stecklina, Julian" <jsteckli@...zon.de>
To:     "corbet@....net" <corbet@....net>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ahmedsoliman0x666@...il.com" <ahmedsoliman0x666@...il.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "ovich00@...il.com" <ovich00@...il.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "igor.stoppa@...il.com" <igor.stoppa@...il.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "nigel.edwards@....com" <nigel.edwards@....com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "ahmedsoliman@...a.vt.edu" <ahmedsoliman@...a.vt.edu>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "blukashev@...pervictus.com" <blukashev@...pervictus.com>
Subject: Re: [PATCH V7 0/10] KVM: X86: Introducing ROE Protection Kernel
 Hardening

Ahmed,

On Fri, 2018-12-07 at 14:47 +0200, Ahmed Abd El Mawgood wrote:
> The reason why it would be better to implement this from inside kvm: instead
> of
> (host) user space is the need to access SPTEs to modify the permissions, while
> mprotect() from user space can work in theory. It will become a big
> performance
> hit to vmexit and switch to user space mode on each fault, on the other hand,
> having the permission handled by EPT should make some remarkable performance
> gain.

Given that writes to these areas should be exceptional occurrences, I don't
understand why this path needs to be optimized. To me it seems, a straight-
forward userspace implementation with no additional code in the kernel achieves
the same feature. Can you elaborate?

Julian



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