linux-hardening - Re: [RFC PATCH v2 18/19] heki: x86: Protect guest kernel memory using the KVM hypervisor

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Date: Mon, 13 Nov 2023 09:54:03 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Mickaël Salaün <mic@...ikod.net>
Cc: 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>,
	Alexander Graf <graf@...zon.com>,
	Chao Peng <chao.p.peng@...ux.intel.com>,
	"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
	Forrest Yuan Yu <yuanyu@...gle.com>,
	James Gowans <jgowans@...zon.com>,
	James Morris <jamorris@...ux.microsoft.com>,
	John Andersen <john.s.andersen@...el.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>,
	Thara Gopinath <tgopinath@...rosoft.com>,
	Trilok Soni <quic_tsoni@...cinc.com>, Wei Liu <wei.liu@...nel.org>,
	Will Deacon <will@...nel.org>,
	Yu Zhang <yu.c.zhang@...ux.intel.com>,
	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 v2 18/19] heki: x86: Protect guest kernel memory
 using the KVM hypervisor

On Sun, Nov 12, 2023 at 09:23:25PM -0500, Mickaël Salaün wrote:
> From: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
> 
> Implement a hypervisor function, kvm_protect_memory() that calls the
> KVM_HC_PROTECT_MEMORY hypercall to request the KVM hypervisor to
> set specified permissions on a list of guest pages.
> 
> Using the protect_memory() function, set proper EPT permissions for all
> guest pages.
> 
> Use the MEM_ATTR_IMMUTABLE property to protect the kernel static
> sections and the boot-time read-only sections. This enables to make sure
> a compromised guest will not be able to change its main physical memory
> page permissions. However, this also disable any feature that may change
> the kernel's text section (e.g., ftrace, Kprobes), but they can still be
> used on kernel modules.
> 
> Module loading/unloading, and eBPF JIT is allowed without restrictions
> for now, but we'll need a way to authenticate these code changes to
> really improve the guests' security. We plan to use module signatures,
> but there is no solution yet to authenticate eBPF programs.
> 
> Being able to use ftrace and Kprobes in a secure way is a challenge not
> solved yet. We're looking for ideas to make this work.
> 
> Likewise, the JUMP_LABEL feature cannot work because the kernel's text
> section is read-only.

What is the actual problem? As is the kernel text map is already RO and
never changed.