linux-kernel - Re: [PATCH v3 1/6] x86/bugs: Add asm helpers for executing VERW

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Date:   Wed, 25 Oct 2023 23:13:46 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.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,
        ak@...ux.intel.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,
        Alyssa Milburn <alyssa.milburn@...el.com>
Subject: Re: [PATCH v3 1/6] x86/bugs: Add asm helpers for executing VERW

On 25/10/2023 11:07 pm, Pawan Gupta wrote:
> On Wed, Oct 25, 2023 at 10:10:41PM +0100, Andrew Cooper wrote:
>>> +.align L1_CACHE_BYTES, 0xcc
>>> +SYM_CODE_START_NOALIGN(mds_verw_sel)
>>> +	UNWIND_HINT_UNDEFINED
>>> +	ANNOTATE_NOENDBR
>>> +	.word __KERNEL_DS
>> You need another .align here.  Otherwise subsequent code will still
>> start in this cacheline and defeat the purpose of trying to keep it
>> separate.
> Right.
>
>>> +SYM_CODE_END(mds_verw_sel);
>> Thinking about it, should this really be CODE and not a data entry?
> Would that require adding a data equivalent of .entry.text and update
> KPTI to keep it mapped? Or is there an easier option?

Leave it right here in .entry.text , but try using SYM_DATA() and
friends.  See whether objtool vomits over the result or not.

And if objtool does vomit over the result, then leaving it as it is in
this patch with SYM_CODE() is good enough.

>
>> P.S. Please CC on the full series.  Far less effort than fishing the
>> rest off lore.
> I didn't realize get_maintainer.pl isn't doing that already. Proposing
> below update to MAINTAINERS:
>
> ---
> From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> Date: Wed, 25 Oct 2023 14:50:41 -0700
> Subject: [PATCH] MAINTAINERS: Update entry for X86 HARDWARE VULNERABILITIES
>
> Add Andrew Cooper to maintainers of hardware vulnerabilities
> mitigations.
>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> ---
>  MAINTAINERS | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2894f0777537..bf8c8707b8f8 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -23382,6 +23382,7 @@ M:	Thomas Gleixner <tglx@...utronix.de>
>  M:	Borislav Petkov <bp@...en8.de>
>  M:	Peter Zijlstra <peterz@...radead.org>
>  M:	Josh Poimboeuf <jpoimboe@...nel.org>
> +M:	Andrew Cooper <andrew.cooper3@...rix.com>

Oh, right.  Perhaps R rather than M seeing as I can't make any time
commitments, but sure.

~Andrew