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

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Message-ID: <20190618165027.GG2790@e103592.cambridge.arm.com>
Date:   Tue, 18 Jun 2019 17:50:28 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, 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>,
        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, Jun 18, 2019 at 06:25:51PM +0200, Florian Weimer wrote:
> * Dave Martin:
> 
> > On Tue, Jun 18, 2019 at 09:00:35AM -0700, Yu-cheng Yu wrote:
> >> On Tue, 2019-06-18 at 18:05 +0200, Florian Weimer wrote:
> >> > * Yu-cheng Yu:
> >> > 
> >> > > > I assumed that it would also parse the main executable and make
> >> > > > adjustments based on that.
> >> > > 
> >> > > Yes, Linux also looks at the main executable's header, but not its
> >> > > NT_GNU_PROPERTY_TYPE_0 if there is a loader.
> >> > > 
> >> > > > 
> >> > > > ld.so can certainly provide whatever the kernel needs.  We need to tweak
> >> > > > the existing loader anyway.
> >> > > > 
> >> > > > No valid statically-linked binaries exist today, so this is not a
> >> > > > consideration at this point.
> >> > > 
> >> > > So from kernel, we look at only PT_GNU_PROPERTY?
> >> > 
> >> > If you don't parse notes/segments in the executable for CET, then yes.
> >> > We can put PT_GNU_PROPERTY into the loader.
> >> 
> >> Thanks!
> >
> > Would this require the kernel and ld.so to be updated in a particular
> > order to avoid breakage?  I don't know enough about RHEL to know how
> > controversial that might be.
> 
> There is no official ld.so that will work with the current userspace
> interface (in this patch submission).  Upstream glibc needs to be
> updated anyway, so yet another change isn't much of an issue.  This is
> not a problem; we knew that something like this might happen.
> 
> Sure, people need a new binutils with backports for PT_GNU_PROPERTY, but
> given that only very few people will build CET binaries with older
> binutils, I think that's not a real issue either.

OK, just wanted to check we weren't missing any requirement for x86.

This approach should satisfy the requirement for arm64 nicely.

Cheers
---Dave