linux-kernel - Re: [PATCH v11 00/23] Enable CET Virtualization

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Message-ID: <aH6CH+x5mCDrvtoz@AUSJOHALLEN.amd.com>
Date: Mon, 21 Jul 2025 13:08:31 -0500
From: John Allen <john.allen@....com>
To: Chao Gao <chao.gao@...el.com>
Cc: Mathias Krause <minipli@...ecurity.net>,
	Xiaoyao Li <xiaoyao.li@...el.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org, seanjc@...gle.com,
	pbonzini@...hat.com, dave.hansen@...el.com,
	rick.p.edgecombe@...el.com, mlevitsk@...hat.com,
	weijiang.yang@...el.com, xin@...or.com,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v11 00/23] Enable CET Virtualization

On Thu, Jul 17, 2025 at 03:57:03PM +0800, Chao Gao wrote:
> On Thu, Jul 17, 2025 at 09:00:04AM +0200, Mathias Krause wrote:
> >On 16.07.25 22:36, John Allen wrote:
> >> On Mon, Jul 07, 2025 at 09:32:37AM +0800, Chao Gao wrote:
> >>> On Mon, Jul 07, 2025 at 12:51:14AM +0800, Xiaoyao Li wrote:
> >>>> Hi Chao,
> >>>>
> >>>> On 7/4/2025 4:49 PM, Chao Gao wrote:
> >>>>> Tests:
> >>>>> ======================
> >>>>> This series passed basic CET user shadow stack test and kernel IBT test in L1
> >>>>> and L2 guest.
> >>>>> The patch series_has_ impact to existing vmx test cases in KVM-unit-tests,the
> >>>>> failures have been fixed here[1].
> >>>>> One new selftest app[2] is introduced for testing CET MSRs accessibilities.
> >>>>>
> >>>>> Note, this series hasn't been tested on AMD platform yet.
> >>>>>
> >>>>> To run user SHSTK test and kernel IBT test in guest, an CET capable platform
> >>>>> is required, e.g., Sapphire Rapids server, and follow below steps to build
> >>>>> the binaries:
> >>>>>
> >>>>> 1. Host kernel: Apply this series to mainline kernel (>= v6.6) and build.
> >>>>>
> >>>>> 2. Guest kernel: Pull kernel (>= v6.6), opt-in CONFIG_X86_KERNEL_IBT
> >>>>> and CONFIG_X86_USER_SHADOW_STACK options. Build with CET enabled gcc versions
> >>>>> (>= 8.5.0).
> >>>>>
> >>>>> 3. Apply CET QEMU patches[3] before build mainline QEMU.
> >>>>
> >>>> You forgot to provide the links of [1][2][3].
> >>>
> >>> Oops, thanks for catching this.
> >>>
> >>> Here are the links:
> >>>
> >>> [1]: KVM-unit-tests fixup:
> >>> https://lore.kernel.org/all/20230913235006.74172-1-weijiang.yang@intel.com/
> >>> [2]: Selftest for CET MSRs:
> >>> https://lore.kernel.org/all/20230914064201.85605-1-weijiang.yang@intel.com/
> >>> [3]: QEMU patch:
> >>> https://lore.kernel.org/all/20230720111445.99509-1-weijiang.yang@intel.com/
> >>>
> >>> Please note that [1] has already been merged. And [3] is an older version of
> >>> CET for QEMU; I plan to post a new version for QEMU after the KVM series is
> >>> merged.
> >> 
> >> Do you happen to have a branch with the in-progress qemu patches you are
> >> testing with? I'm working on testing on AMD and I'm having issues
> >> getting this old version of the series to work properly.
> 
> Hi John,
> 
> Try this branch:
> 
> https://github.com/gaochaointel/qemu-dev qemu-cet
> 
> Disclaimer: I haven't cleaned up the QEMU patches yet, so they are not of
> upstream quality.
> 
> >
> >For me the old patches worked by changing the #define of
> >MSR_KVM_GUEST_SSP from 0x4b564d09 to 0x4b564dff -- on top of QEMU 9.0.1,
> >that is.
> 
> Please note that aliasing guest SSP to the virtual MSR indexed by 0x4b564dff is
> not part of KVM uAPI in the v11 series. This means the index 0x4b564dff isn't
> stable; userspace should read/write guest SSP via KVM_GET/SET_ONE_REG ioctls.

Thanks, tested on AMD. There's a couple of minor details I still need to
work out, but I should have an updated SVM series out soon.

Tested-by: John Allen <john.allen@....com>