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

On Tue, Jun 18, 2019 at 10:12:50AM +0100, Dave Martin wrote:

On Mon, Jun 17, 2019 at 02:20:40PM +0200, Thomas Gleixner wrote:

quoted

On Mon, 17 Jun 2019, Florian Weimer wrote:

quoted

* Dave Martin:

quoted

On Tue, Jun 11, 2019 at 12:31:34PM -0700, Yu-cheng Yu wrote:

quoted

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

For arm64, we can check for PT_GNU_PROPERTY and then give up
unconditionally.

For x86, we would fall back to PT_NOTE scanning, but this will add a bit
of cost to binaries that don't have NT_GNU_PROPERTY_TYPE_0.  The ld.so
version doesn't tell you what ELF ABI a given executable conforms to.

Since this sounds like it's largely a distro-specific issue, maybe there
could be a Kconfig option to turn the fallback PT_NOTE scanning on?

I'm worried that this causes interop issues similarly to what we see
with VSYSCALL today.  If we need both and a way to disable it, it should
be something like a personality flag which can be configured for each
process tree separately.  Ideally, we'd settle on one correct approach
(i.e., either always process both, or only process PT_GNU_PROPERTY) and
enforce that.

Chose one and only the one which makes technically sense and is not some
horrible vehicle.

Everytime we did those 'oh we need to make x fly workarounds' we regretted
it sooner than later.

So I guess that points to keeping PT_NOTE scanning always available as a
fallback on x86.  This sucks a bit, but if there are binaries already in
the wild that rely on this, I don't think we have much choice...

I'm not sure I read Thomas' comment like that. In my reading keeping the
PT_NOTE fallback is exactly one of those 'fly workarounds'. By not
supporting PT_NOTE only the 'fine' people already shit^Hpping this out
of tree are affected, and we don't have to care about them at all.