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

[Yu-cheng Yu]

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