linux-kernel - Re: [PATCH 00/24] objtool: retpoline and asm-goto validation

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Message-ID: <20180123160350.GK2228@hirez.programming.kicks-ass.net>
Date:   Tue, 23 Jan 2018 17:03:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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>
Subject: Re: [PATCH 00/24] objtool: retpoline and asm-goto validation

On Tue, Jan 23, 2018 at 03:57:39PM +0000, David Woodhouse wrote:
> On Tue, 2018-01-23 at 16:42 +0100, Peter Zijlstra wrote:
> > drivers/watchdog/.tmp_hpwdt.o: warning: objtool: .text+0x24: indirect call found in RETPOLINE build
> 
> You're calling into BIOS there. Not a lot of point in protecting that
> one. This is one of the cases where we were saying you needed to turn
> on IBRS to have complete protection, even with retpoline.
> 

That code looked entirely dodgy, which is why I left it. I can easily
add the ANNOTATE_RETPOLINE_SAFE thing to shut it up, but given it is an
actual problem, maybe we should just keep it?