linux-kernel - Re: [RFC PATCH 00/18] KVM: VMX: Introduce Intel Mode-Based Execute Control (MBEC)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aCJsSvc4_azZNrKI@google.com>
Date: Mon, 12 May 2025 14:46:50 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Jon Kohler <jon@...anix.com>
Cc: pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Alexander Grest <Alexander.Grest@...rosoft.com>, Nicolas Saenz Julienne <nsaenz@...zon.es>, 
	"Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>, 
	"Mickaël Salaün" <mic@...ikod.net>, Tao Su <tao1.su@...ux.intel.com>, 
	Xiaoyao Li <xiaoyao.li@...el.com>, Zhao Liu <zhao1.liu@...el.com>
Subject: Re: [RFC PATCH 00/18] KVM: VMX: Introduce Intel Mode-Based Execute
 Control (MBEC)

On Thu, Mar 13, 2025, Jon Kohler wrote:
> ## Summary
> This series introduces support for Intel Mode-Based Execute Control
> (MBEC) to KVM and nested VMX virtualization, aiming to significantly
> reduce VMexits and improve performance for Windows guests running with
> Hypervisor-Protected Code Integrity (HVCI).

...

> ## Testing
> Initial testing has been on done on 6.12-based code with:
>   Guests
>     - Windows 11 24H2 26100.2894
>     - Windows Server 2025 24H2 26100.2894
>     - Windows Server 2022 W1H2 20348.825
>   Processors:
>     - Intel Skylake 6154
>     - Intel Sapphire Rapids 6444Y

This series needs testcases, and lots of 'em.  A short list off the top of my head:

 - New KVM-Unit-Test (KUT) ept_access_xxx testcases to verify KVM does the right
   thing with respect to user and supervisor code fetches when MBEC is:

     1. Supported and Enabled
     2. Supported but Disabled
     3. Unsupported

 - KUT testcases to verify VMLAUNCH/VMRESUME consistency checks.

 - KUT testcases to verify KVM treats WRITABLE+USER_EXEC as an illegal combination,
   i.e. that MBEC doesn't affect the W=1,R=0 behavior.

The access tests in particular absolutely need to be provided along with the next
version.  Unless I'm missing something, this RFC implementation is buggy throughout
due to tracking MBEC on a per-vCPU basis, and all of those bugs should be exposed
by even relative basic testcases.