linux-kernel - Re: [PATCH v7 22/27] binfmt_elf: Extract .note.gnu.property from an ELF file

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Message-ID: <031bc55d8dcdcf4f031e6ff27c33fd52c61d33a5.camel@intel.com>
Date:   Tue, 11 Jun 2019 12:31:34 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Dave Martin <Dave.Martin@....com>,
        Florian Weimer <fweimer@...hat.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Subject: Re: [PATCH v7 22/27] binfmt_elf: Extract .note.gnu.property from an
 ELF file

On Tue, 2019-06-11 at 12:41 +0100, Dave Martin wrote:
> On Mon, Jun 10, 2019 at 07:24:43PM +0200, Florian Weimer wrote:
> > * Yu-cheng Yu:
> > 
> > > To me, looking at PT_GNU_PROPERTY and not trying to support anything is a
> > > logical choice.  And it breaks only a limited set of toolchains.
> > > 
> > > I will simplify the parser and leave this patch as-is for anyone who wants
> > > to
> > > back-port.  Are there any objections or concerns?
> > 
> > Red Hat Enterprise Linux 8 does not use PT_GNU_PROPERTY and is probably
> > the largest collection of CET-enabled binaries that exists today.
> 
> For clarity, RHEL is actively parsing these properties today?
> 
> > My hope was that we would backport the upstream kernel patches for CET,
> > port the glibc dynamic loader to the new kernel interface, and be ready
> > to run with CET enabled in principle (except that porting userspace
> > libraries such as OpenSSL has not really started upstream, so many
> > processes where CET is particularly desirable will still run without
> > it).
> > 
> > I'm not sure if it is a good idea to port the legacy support if it's not
> > part of the mainline kernel because it comes awfully close to creating
> > our own private ABI.
> 
> I guess we can aim to factor things so that PT_NOTE scanning is
> available as a fallback on arches for which the absence of
> PT_GNU_PROPERTY is not authoritative.

We can probably check PT_GNU_PROPERTY first, and fallback (based on ld-linux
version?) to PT_NOTE scanning?

Yu-cheng