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? Cheers ---Dave
