linux-kernel - Re: [PATCH 08/24] x86,sme: Annotate indirect call

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Message-ID: <20180131160018.GU2269@hirez.programming.kicks-ass.net>
Date:   Wed, 31 Jan 2018 17:00:18 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Jason Baron <jbaron@...mai.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 08/24] x86,sme: Annotate indirect call

On Wed, Jan 31, 2018 at 09:04:51AM -0600, Josh Poimboeuf wrote:
> If there's no harm, it would be simpler and more robust to just do
> retpolines everywhere and not worry about special cases.
> 
> (Forgetting paravirt for the moment, which is the eternal "special
> case".)
> 
> I was also thinking about adding a debug option for _runtime_ retpoline
> verification that decodes all kernel text and reports any indirect
> branches it finds (yes, kind of like an in-kernel objtool).  That would
> be a lot more straightforward without special cases.  Obviously
> .init.text wouldn't be a problem there, but the other annotated safe
> locations would.

Like said, even retpolines themselves need annotation. We could simply
keep the section and not .discard. it.