Re: [PATCH 7/7] selftests/x86: Add tests for signal frame FPU portability

[Andrei Vagin]

On Thu, Sep 24, 2026 at 11:54 AM Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Thu, Sep 24, 2026 at 04:16:03AM +0000, Andrei Vagin wrote:
> > Add a new selftest tools/testing/selftests/x86/sigframe_fpu_portability.c
> > to verify signal frame portability and consistency when the xstate size
> > is shrunk:
> >
> > - test_valid_shrunk_xstate_size: Verifies that the kernel correctly
> >   restores the xstate context from a signal frame where xstate_size has
> >   been manually shrunk to only cover active features, as long as the
> >   FP_XSTATE_MAGIC2 marker is correctly placed. This simulates migrating
> >   a process created on a host with fewer xstate features to a host with
> >   more features.
> >
> > - test_invalid_shrunk_xstate_size: Verifies that the kernel rejects
> >   (via SIGSEGV) a signal frame where xstate_size is smaller than required
> >   by the enabled features in the xfeatures mask.
> >
> > Reviewed-by: Alexander Mikhalitsyn <alexander@xxxxxxxxxxxxx>
> > Reviewed-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
> > Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
> > ---
> >  tools/testing/selftests/x86/Makefile          |   5 +-
> >  .../selftests/x86/sigframe_fpu_portability.c  | 246 ++++++++++++++++++
> >  tools/testing/selftests/x86/xstate.c          |  12 -
> >  tools/testing/selftests/x86/xstate.h          |  20 ++
> >  4 files changed, 270 insertions(+), 13 deletions(-)
> >  create mode 100644 tools/testing/selftests/x86/sigframe_fpu_portability.c
>
> Sashiko has a comment which sounds valid to me but I haven't looked at the
> surrounding code:
>
> https://sashiko.dev/#/patchset/20260924041604.3209659-1-avagin%40google.com

Thank you for pointing this out. Sashiko didn't report anything on the
v6 version, and this test hasn't been changed since then. I combined
%ymm0 load/store and the kill syscall into a single inline assembly,
so I think it should address Sashiko's concerns. I've sent v8, let's see
what Sashiko reports on it.

Thanks,
Andrei