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

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Message-ID: <20231025212806.pgykrxzcmbhrhix5@treble>
Date:   Wed, 25 Oct 2023 14:28:06 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Andrew Cooper <andrew.cooper3@...rix.com>
Cc:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        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>,
        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 Wed, Oct 25, 2023 at 10:10:41PM +0100, Andrew Cooper wrote:
> On 25/10/2023 9:52 pm, Pawan Gupta wrote:
> > diff --git a/arch/x86/entry/entry.S b/arch/x86/entry/entry.S
> > index bfb7bcb362bc..f8ba0c0b6e60 100644
> > --- a/arch/x86/entry/entry.S
> > +++ b/arch/x86/entry/entry.S
> > @@ -20,3 +23,16 @@ SYM_FUNC_END(entry_ibpb)
> >  EXPORT_SYMBOL_GPL(entry_ibpb);
> >  
> >  .popsection
> > +
> > +.pushsection .entry.text, "ax"
> > +
> > +.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.
> 
> > +SYM_CODE_END(mds_verw_sel);
> 
> Thinking about it, should this really be CODE and not a data entry?
> 
> It lives in .entry.text but it really is data and objtool shouldn't be
> writing ORC data for it at all.
> 
> (Not to mention that if it's marked as STT_OBJECT, objdump -d will do
> the sensible thing and not even try to disassemble it).
> 
> ~Andrew
> 
> P.S. Please CC on the full series.  Far less effort than fishing the
> rest off lore.

+1 to putting it in .rodata or so.

-- 
Josh