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Re: [PATCH] x86: Support IBT and SHSTK in Intel CET [BZ #21598]
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Joseph Myers <joseph at codesourcery dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>, Igor Tsimbalist <igor dot v dot tsimbalist at intel dot com>, Andrew Senkevich <andrew dot n dot senkevich at gmail dot com>
- Date: Tue, 19 Dec 2017 10:34:48 -0800
- Subject: Re: [PATCH] x86: Support IBT and SHSTK in Intel CET [BZ #21598]
- Authentication-results: sourceware.org; auth=none
- References: <20171219134500.GA1143@gmail.com> <alpine.DEB.firstname.lastname@example.org>
On Tue, Dec 19, 2017 at 8:47 AM, Joseph Myers <email@example.com> wrote:
> On Tue, 19 Dec 2017, H.J. Lu wrote:
>> b. Otherwise lock SHSTK.
>> 3. After SHSTK is enabled, it is an error to load a shared object
>> without GNU_PROPERTY_X86_FEATURE_1_SHSTK.
> This seems like something that would be unsafe to enable by default in
> glibc / the toolchain as a whole, because it would mean that rebuilding a
> program (and the shared libraries it uses at startup) stops it from
> dlopening existing shared objects. That is, making it an error to load
> existing shared objects should only be enabled by an explicit non-default
> option (whether configure-time option for glibc, or link-time option for
> programs that do not use dlopen) that is only used when building for a
> system where it is known that there is no need to be able to dlopen any
> existing shared object.
>> We will submit a separate patch for kernel interface when kernel API
>> is settled.
> What depends on the kernel interface? Is this anything to do with all the
> FIXMEs in the code?
> The presence of those FIXMEs and unknown kernel interface suggests to me
> that this is not ready for 2.27 and should be reconsidered at some point
> in the 2.28 cycle or later, once the kernel support is in Linus's git
We will do it for glibc 2.28.
>> (CFLAGS-tst-context1.c): Add -fcf-protection=branch -mno-shstk
>> (CFLAGS-bug-getcontext.c): Likewise.
>> (CFLAGS-tst-makecontext.c): Likewise.
>> (CFLAGS-tst-makecontext2.c): Likewise.
>> (CFLAGS-tst-makecontext3.c): Likewise.
>> (CFLAGS-tst-setcontext.c): Likewise.
>> (CFLAGS-tst-setcontext2.c): Likewise.
>> (CFLAGS-tst-setcontext3.c): Likewise.
>> (CFLAGS-tst-xbzero-opt.c): Likewise.
> If you need those options for certain tests, I'd expect them to be needed
> for building conform/ tests as well, but don't see anything that would add
> them for those tests.
>> sysdeps/unix/sysv/linux/x86/ucontext.h | 56 +++++++++
> Again, adding sysdeps versions of installed headers that are not bits/*,
> or to a lesser extent sys/*, is a bad idea because those headers are
> liable to get out of sync with the main versions; people don't expect such
> headers to have multiple versions.
> If you need to do something differently in this header for x86, you should
> add a bits/ header which has an x86-specific version.
I will do it.
>> diff --git a/sysdeps/unix/sysv/linux/x86/check-cet.awk b/sysdeps/unix/sysv/linux/x86/check-cet.awk
>> new file mode 100644
>> index 0000000000..e3723f4839
>> --- /dev/null
>> +++ b/sysdeps/unix/sysv/linux/x86/check-cet.awk
>> @@ -0,0 +1,35 @@
>> +# This awk script expects to get command-line files that are each
> Should start with a one-line description of the file, then copyright and
> license notices.
I will fix it.