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