linux-kernel - Re: [PATCH v6 6/6] KVM: VMX: Move VERW closer to VMentry for MDS mitigation

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Message-ID: <20240201011129.rmuhpl6iwpozpll6@desk>
Date: Wed, 31 Jan 2024 17:12:05 -0800
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Andy Lutomirski <luto@...nel.org>, Jonathan Corbet <corbet@....net>,
	Paolo Bonzini <pbonzini@...hat.com>, tony.luck@...el.com,
	ak@...ux.intel.com, tim.c.chen@...ux.intel.com,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	kvm@...r.kernel.org,
	Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
	antonio.gomez.iglesias@...ux.intel.com
Subject: Re: [PATCH  v6 6/6] KVM: VMX: Move VERW closer to VMentry for MDS
 mitigation

On Fri, Jan 26, 2024 at 01:31:54PM -0800, Sean Christopherson wrote:
> On Tue, Jan 23, 2024, Pawan Gupta wrote:
> > During VMentry VERW is executed to mitigate MDS. After VERW, any memory
> > access like register push onto stack may put host data in MDS affected
> > CPU buffers. A guest can then use MDS to sample host data.
> > 
> > Although likelihood of secrets surviving in registers at current VERW
> > callsite is less, but it can't be ruled out. Harden the MDS mitigation
> > by moving the VERW mitigation late in VMentry path.
> > 
> > Note that VERW for MMIO Stale Data mitigation is unchanged because of
> > the complexity of per-guest conditional VERW which is not easy to handle
> > that late in asm with no GPRs available. If the CPU is also affected by
> > MDS, VERW is unconditionally executed late in asm regardless of guest
> > having MMIO access.
> > 
> > Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> > ---
> 
> Acked-by: Sean Christopherson <seanjc@...gle.com>

Thanks.