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RFC: adding Linux vsyscall-disable and similar backwards-incompatibility flags to ELF headers?
- From: Andy Lutomirski <luto at amacapital dot net>
- To: Kees Cook <keescook at chromium dot org>, "linux-kernel at vger dot kernel dot org" <linux-kernel at vger dot kernel dot org>, libc-alpha <libc-alpha at sourceware dot org>, "musl at lists dot openwall dot com" <musl at lists dot openwall dot com>, gcc at gcc dot gnu dot org, Binutils <binutils at sourceware dot org>
- Date: Tue, 1 Sep 2015 17:51:44 -0700
- Subject: RFC: adding Linux vsyscall-disable and similar backwards-incompatibility flags to ELF headers?
- Authentication-results: sourceware.org; auth=none
Linux has a handful of weird features that are only supported for
backwards compatibility. The big one is the x86_64 vsyscall page, but
uselib probably belongs on the list, too, and we might end up with
more at some point.
I'd like to add a way that new programs can turn these features off.
In particular, I want the vsyscall page to be completely gone from the
perspective of any new enough program. This is straightforward if we
add a system call to ask for the vsyscall page to be disabled, but I'm
wondering if we can come up with a non-syscall way to do it.
I think that the ideal behavior would be that anything linked against
a sufficiently new libc would be detected, but I don't see a good way
to do that using existing toolchain features.
Ideas? We could add a new phdr for this, but then we'd need to play
linker script games, and I'm not sure that could be done in a clean,