linux-hardening - Re: [RFC PATCH v1 0/9] Hypervisor-Enforced Kernel Integrity

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Date:   Wed, 24 May 2023 14:04:07 -0700
From:   Trilok Soni <quic_tsoni@...cinc.com>
To:     Mickaël Salaün <mic@...ikod.net>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>
CC:     Alexander Graf <graf@...zon.com>,
        Forrest Yuan Yu <yuanyu@...gle.com>,
        James Morris <jamorris@...ux.microsoft.com>,
        John Andersen <john.s.andersen@...el.com>,
        Liran Alon <liran.alon@...cle.com>,
        "Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>,
        Marian Rotariu <marian.c.rotariu@...il.com>,
        Mihai Donțu <mdontu@...defender.com>,
        Nicușor Cîțu <nicu.citu@...oud.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Thara Gopinath <tgopinath@...rosoft.com>,
        Will Deacon <will@...nel.org>,
        Zahra Tarkhani <ztarkhani@...rosoft.com>,
        Ștefan Șicleru <ssicleru@...defender.com>,
        <dev@...ts.cloudhypervisor.org>, <kvm@...r.kernel.org>,
        <linux-hardening@...r.kernel.org>, <linux-hyperv@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>, <qemu-devel@...gnu.org>,
        <virtualization@...ts.linux-foundation.org>, <x86@...nel.org>,
        <xen-devel@...ts.xenproject.org>
Subject: Re: [RFC PATCH v1 0/9] Hypervisor-Enforced Kernel Integrity

On 5/5/2023 8:20 AM, Mickaël Salaün wrote:
> Hi,
> 
> This patch series is a proof-of-concept that implements new KVM features
> (extended page tracking, MBEC support, CR pinning) and defines a new API to
> protect guest VMs. No VMM (e.g., Qemu) modification is required.
> 
> The main idea being that kernel self-protection mechanisms should be delegated
> to a more privileged part of the system, hence the hypervisor. It is still the
> role of the guest kernel to request such restrictions according to its

Only for the guest kernel images here? Why not for the host OS kernel? 
Embedded devices w/ Android you have mentioned below supports the host 
OS as well it seems, right?

Do we suggest that all the functionalities should be implemented in the 
Hypervisor (NS-EL2 for ARM) or even at Secure EL like Secure-EL1 (ARM).

I am hoping that whatever we suggest the interface here from the Guest 
to the Hypervisor becomes the ABI right?


> 
> # Current limitations
> 
> The main limitation of this patch series is the statically enforced
> permissions. This is not an issue for kernels without module but this needs to
> be addressed.  Mechanisms that dynamically impact kernel executable memory are
> not handled for now (e.g., kernel modules, tracepoints, eBPF JIT), and such
> code will need to be authenticated.  Because the hypervisor is highly
> privileged and critical to the security of all the VMs, we don't want to
> implement a code authentication mechanism in the hypervisor itself but delegate
> this verification to something much less privileged. We are thinking of two
> ways to solve this: implement this verification in the VMM or spawn a dedicated
> special VM (similar to Windows's VBS). There are pros on cons to each approach:
> complexity, verification code ownership (guest's or VMM's), access to guest
> memory (i.e., confidential computing).

Do you foresee the performance regressions due to lot of tracking here? 
Production kernels do have lot of tracepoints and we use it as feature 
in the GKI kernel for the vendor hooks implementation and in those cases 
every vendor driver is a module. Separate VM further fragments this 
design and delegates more of it to proprietary solutions?

Do you have any performance numbers w/ current RFC?

---Trilok Soni