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

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Message-ID: <20200114165135.GK31032@zn.tnic>
Date:   Tue, 14 Jan 2020 17:51:35 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Kees Cook <keescook@...omium.org>, "H. Peter Anvin" <hpa@...or.com>
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 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?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette