linux-kernel - Re: [PATCH V5 0/5] KVM: X86: Introducing ROE Protection Kernel Hardening

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Message-Id: <e778a30c-f32e-eb4c-5492-21c81926b87f@de.ibm.com>
Date:   Tue, 30 Oct 2018 18:31:38 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Ahmed Abd El Mawgood <ahmedsoliman0x666@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>, rkrcmar@...hat.com,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, x86@...nel.org, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        ovich00@...il.com, kernel-hardening@...ts.openwall.com,
        nigel.edwards@....com, Boris Lukashev <blukashev@...pervictus.com>,
        Hossam Hassan <7ossam9063@...il.com>,
        Ahmed Lotfy <A7med.lotfey@...il.com>
Subject: Re: [PATCH V5 0/5] KVM: X86: Introducing ROE Protection Kernel
 Hardening


On 10/26/2018 05:12 PM, Ahmed Abd El Mawgood wrote:
> This is the 5th version which is 4th version with minor fixes. ROE is a 
> hypercall that enables host operating system to restrict guest's access to its
> own memory. This will provide a hardening mechanism that can be used to stop
> rootkits from manipulating kernel static data structures and code. Once a memory
> region is protected the guest kernel can't even request undoing the protection.

At the KVM forum we considered this as something that could be implemented across
multiple architectures. Yes, there will be architecture specific implementations 
and yes some  architectures might be not able to provide everything (e.g. sub-page
granularity).
But we should really check if we can come up with a guest interface or guest common 
code that can be useful across architectures.
> 
> Memory protected by ROE should be non-swapable because even if the ROE protected
> page got swapped out, It won't be possible to write anything in its place.
> 
> ROE hypercall should be capable of either protecting a whole memory frame or
> parts of it. With these two, it should be possible for guest kernel to protect
> its memory and all the page table entries for that memory inside the page table.
> I am still not sure whether this should be part of ROE job or the guest's job.
> 
> 
> 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.
> 
> Our model assumes that an attacker got full root access to a running guest and
> his goal is to manipulate kernel code/data (hook syscalls, overwrite IDT ..etc).
> 
> There is future work in progress to also put some sort of protection on the page
> table register CR3 and other critical registers that can be intercepted by KVM.
> This way it won't be possible for an attacker to manipulate any part of the
> guests page table.
> 
> V4->V5 change log:
> - Fixed summary (it was reverted summary)
> - Fixed an inaccurate documentation in patch [4/5]
> 
> Summary:
> 
>  Documentation/virtual/kvm/hypercalls.txt |  40 +++++
>  arch/x86/include/asm/kvm_host.h          |  11 +-
>  arch/x86/kvm/Kconfig                     |   7 +
>  arch/x86/kvm/mmu.c                       | 129 ++++++++++----
>  arch/x86/kvm/vmx.c                       |   2 +-
>  arch/x86/kvm/x86.c                       | 281 ++++++++++++++++++++++++++++++-
>  include/linux/kvm_host.h                 |  29 ++++
>  include/uapi/linux/kvm_para.h            |   5 +
>  virt/kvm/kvm_main.c                      | 119 +++++++++++--
>  9 files changed, 572 insertions(+), 51 deletions(-)
> 
> Signed-off-by: Ahmed Abd El Mawgood <ahmedsoliman0x666@...il.com>
>