On Wed, Jun 12, 2019 at 12:04:01PM -0700, Yu-cheng Yu wrote: > On Wed, 2019-06-12 at 10:32 +0100, Dave Martin wrote: > > 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? > > Yes, I will make it a Kconfig option. OK, that works for me. This would also help keep the PT_NOTE scanning separate from the rest of the code. For arm64 we could then unconditionally select/deselect that option, where x86 could leave it configurable either way. Cheers ---Dave
