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

From: Thomas Gleixner <tglx@linutronix.de>
To: Florian Weimer <fweimer@redhat.com>
Cc: Dave Martin <Dave.Martin@arm.com>,
	Yu-cheng Yu <yu-cheng.yu@intel.com>,
	 x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	 Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org,  linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	 linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	 Andy Lutomirski <luto@amacapital.net>,
	 Balbir Singh <bsingharora@gmail.com>,
	Borislav Petkov <bp@alien8.de>,
	 Cyrill Gorcunov <gorcunov@gmail.com>,
	 Dave Hansen <dave.hansen@linux.intel.com>,
	 Eugene Syromiatnikov <esyr@redhat.com>,
	"H.J. Lu" <hjl.tools@gmail.com>,  Jann Horn <jannh@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	 Kees Cook <keescook@chromium.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	 Nadav Amit <nadav.amit@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>,  Pavel Machek <pavel@ucw.cz>,
	Peter Zijlstra <peterz@infradead.org>,
	 Randy Dunlap <rdunlap@infradead.org>,
	 "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	 Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>
Subject: Re: [PATCH v7 22/27] binfmt_elf: Extract .note.gnu.property from an ELF file
Date: Mon, 17 Jun 2019 14:20:40 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1906171418220.1854@nanos.tec.linutronix.de> (raw)
In-Reply-To: <87imt4jwpt.fsf@oldenburg2.str.redhat.com>

On Mon, 17 Jun 2019, Florian Weimer wrote:
> * Dave Martin:
> > On Tue, Jun 11, 2019 at 12:31:34PM -0700, Yu-cheng Yu wrote:
> >> 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.

Thanks,

	tglx