Re: [PATCH] x86: Support IBT and SHSTK in Intel CET [BZ #21598]

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Tue, Dec 19, 2017 at 8:47 AM, Joseph Myers <joseph@codesourcery.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
> tree.

We will do it for glibc 2.28.

>>       (CFLAGS-tst-context1.c): Add -fcf-protection=branch -mno-shstk
>>       -mibt.
>>       (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.


-- 
H.J.