linux-kernel - Re: [PATCH 0/7] objtool: retpoline validation

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Message-ID: <20180201153235.GZ2249@hirez.programming.kicks-ass.net>
Date:   Thu, 1 Feb 2018 16:32:35 +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>
Subject: Re: [PATCH 0/7] objtool: retpoline validation

On Thu, Feb 01, 2018 at 09:28:56AM -0600, Josh Poimboeuf wrote:
> On Thu, Feb 01, 2018 at 03:34:21PM +0100, Peter Zijlstra wrote:
> > There are the retpoline validation patches; they work with the __noretpoline
> > thing from David.
> 
> Have you run this through 0-day bot yet? 

Yes, it complains a _lot_ because no retpoline supported compiler.

> A manual awk/sed found another
> one, which objtool confirms:
> 
>   drivers/watchdog/.tmp_hpwdt.o: warning: objtool: .text+0x24: indirect call found in RETPOLINE build

That is the only known one left. It calls into BIOS code, so its not
safe and using a retpoline for it is pointless since nobody audited the
BIOS code.