linux-kernel - Re: [PATCH v3] x86/vmlinux: Fix vmlinux.lds.S with pre-2.23 binutils

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Message-ID: <27433E59-971A-4885-B74C-2D6844372FE6@zytor.com>
Date:   Tue, 14 Jan 2020 13:50:05 -0800
From:   hpa@...or.com
To:     Borislav Petkov <bp@...en8.de>, Kees Cook <keescook@...omium.org>
CC:     Arvind Sankar <nivedita@...m.mit.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Thomas Lendacky <Thomas.Lendacky@....com>,
        Mauro Rossi <issor.oruam@...il.com>,
        Michael Matz <matz@...e.de>
Subject: Re: [PATCH v3] x86/vmlinux: Fix vmlinux.lds.S with pre-2.23 binutils

On January 14, 2020 8:51:35 AM PST, Borislav Petkov <bp@...en8.de> wrote:
>On Mon, Jan 13, 2020 at 05:53:32PM -0800, Kees Cook wrote:
>> NAK: linkers can add things at the end of .text that will go missing
>from
>> the kernel if _etext isn't _outside_ the .text section, truly beyond
>the
>> end of the .text section. This patch will break Control Flow
>Integrity
>> checking since the jump tables are at the end of .text.
>
>Err, which linkers are those? Please elaborate.
>
>In any case, after reading the thread, I can't help but favor the idea
>of us bumping min binutils version to 2.23.
>
>Michael (on Cc) says that the 2.21 was kinda broken wrt to the symbols
>fun outside of sections, 2.22 tried to fix it, see
>
>fd952815307f ("x86-32, relocs: Whitelist more symbols for ld bug
>workaround")
>
>which Arvind pointed out and 2.23 fixed it for real.
>
>Now, 2.23 is still very ancient. I'm looking at our releases: openSUSE
>12.1 has the minimum supported gcc version 4.6 by the kernel and
>also the minimum binutils version 2.21 which we support according to
>Documentation/process/changes.rst
>
>Now, openSUSE 12.1 is ancient and we ourselves advise people to update
>to current distros so I don't think anyone would still run it.
>
>So, considering that upping the binutils version would save us from all
>this trouble I say we try it after 5.5 releases for a maximum time of a
>full 5.6 release cycle and see who complains.
>
>Considering how no one triggered this yet until Arvind, I think no one
>would complain. But I might be wrong.
>
>So what do people think? hpa?

I'm all for dumping support for an ancient, known buggy binutils.
-- 
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