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

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Message-ID: <20180201174335.3tccxfotu7slriuu@treble>
Date:   Thu, 1 Feb 2018 11:43:35 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 06:14:27PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 01, 2018 at 04:51:35PM +0000, David Woodhouse wrote:
> > > Ideally we'd have a way to mark the module 'unsafe' or something.
> > 
> > No, we just need to set IBRS before doing it. 
> 
> That would work, assuming IBRS is available to begin with of course. Do
> we WARN if we hit this code and don't have IBRS available?

Perhaps it should just be reported in the spectre_v2 sysfs file.

So

  "Mitigation: Full generic retpoline"

would instead be something like

  "Vulnerable: Retpoline without IBRS"

?

> > The same applies to any
> > EFI runtime calls, APM and all kinds of other random crap that calls
> > into firmware. I'm not sure why those aren't showing up.
> 
> arch/x86/platform/efi/Makefile:OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
> arch/x86/platform/efi/Makefile:OBJECT_FILES_NON_STANDARD_efi_stub_$(BITS).o := y
> 
> And similar things tell objtool to please not look..

Right, some of the corner cases like efi, vdso, and bpf tend to be
ignored by objtool right now.

-- 
Josh