linux-kernel - Re: [PATCH 3/6] x86/entry_32: Add VERW just before userspace transition

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Date:   Fri, 20 Oct 2023 16:49:34 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.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>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, tony.luck@...el.com,
        tim.c.chen@...ux.intel.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  3/6] x86/entry_32: Add VERW just before userspace
 transition

On Fri, Oct 20, 2023 at 01:45:09PM -0700, Pawan Gupta wrote:
> As done for entry_64, add support for executing VERW late in exit to
> user path for 32-bit mode.
> 
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> ---
>  arch/x86/entry/entry_32.S | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
> index 6e6af42e044a..bbf77d2aab2e 100644
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -886,6 +886,9 @@ SYM_FUNC_START(entry_SYSENTER_32)
>  	popfl
>  	popl	%eax
>  
> +	/* Mitigate CPU data sampling attacks .e.g. MDS */
> +	USER_CLEAR_CPU_BUFFERS
> +
>  	/*
>  	 * Return back to the vDSO, which will pop ecx and edx.
>  	 * Don't bother with DS and ES (they already contain __USER_DS).

Did you forget the INT 0x80 entry point?

-Andi