Date: Fri, 20 Jul 2018 02:26:46 +0200 From: Ahmed Soliman <ahmedsoliman0x666@...il.com> To: Jann Horn <jannh@...gle.com> Cc: kvm@...r.kernel.org, Kernel Hardening <kernel-hardening@...ts.openwall.com>, virtualization@...ts.linux-foundation.org, linux-doc@...r.kernel.org, "the arch/x86 maintainers" <x86@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Radim Krčmář <rkrcmar@...hat.com>, Jonathan Corbet <corbet@....net>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, David Hildenbrand <david@...hat.com>, Boris Lukashev <blukashev@...pervictus.com>, David Vrabel <david.vrabel@...anix.com>, nigel.edwards@....com, Rik van Riel <riel@...riel.com> Subject: Re: [PATCH 3/3] [RFC V3] KVM: X86: Adding skeleton for Memory ROE On 20 July 2018 at 00:59, Jann Horn <jannh@...gle.com> wrote: > On Thu, Jul 19, 2018 at 11:40 PM Ahmed Abd El Mawgood > Why are you implementing this in the kernel, instead of doing it in > host userspace? I thought about implementing it completely in QEMU but It won't be possible for few reasons: - After talking to QEMU folks I came up to conclusion that it when it comes to managing memory allocated for guest, it is always better to let KVM handles everything, unless there is a good reason to play with that memory chunk inside QEMU itself. - But actually there is a good reason for implementing ROE in kernel space, it is that ROE is architecture dependent to great extent. I should have emphasized that the only currently supported architecture is X86. I am not sure how deep the dependency on architecture goes. But as for now the current set of patches does a SPTE enumeration as part of the process. To my best knowledge, this isn't exposed outside arch/x68/kvm let alone having a host user space interface for it. Also the way I am planning to protect TLB from malicious gva -> gpa mapping is by knowing that in x86 it is possible to VMEXIT on page faults, I am not sure if it will safe to assume that all kvm supported architectures will behave this way. For these reasons I thought it will be better if arch dependent stuff (the mechanism implementation) is kept in arch/*/kvm folder and with minimal modifications to virt/kvm/* after setting a kconfig variable to enable ROE. But I left room for the user space app using kvm to decide the rightful policy for handling ROE violations. The way it works by KVM_EXIT_MMIO error to user space, keeping all the architectural details hidden away from user space. A last note is that I didn't create this from scratch, instead I extended KVM_MEM_READONLY implementation to also allow R/O per page instead R/O per whole slot which is already done in kernel space.
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