linux-kernel - [GIT PULL] siginfo: ABI fixes for v5.13-rc3

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Date:   Fri, 21 May 2021 09:59:53 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Florian Weimer <fweimer@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Collingbourne <pcc@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        sparclinux <sparclinux@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Marco Elver <elver@...gle.com>
Subject: [GIT PULL] siginfo: ABI fixes for v5.13-rc3


Linus,

Please pull the for-v5.13-rc3 branch from the git tree:

  git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git for-v5.13-rc3

  HEAD: 922e3013046b79b444c87eda5baf43afae1326a8 signalfd: Remove SIL_FAULT_PERF_EVENT fields from signalfd_siginfo


During the merge window an issue with si_perf and the siginfo ABI came
up.  The alpha and sparc siginfo structure layout had changed with the
addition of SIGTRAP TRAP_PERF and the new field si_perf.

The reason only alpha and sparc were affected is that they are the
only architectures that use si_trapno.

Looking deeper it was discovered that si_trapno is used for only
a few select signals on alpha and sparc, and that none of the
other _sigfault fields past si_addr are used at all.  Which means
technically no regression on alpha and sparc.

While the alignment concerns might be dismissed the abuse of
si_errno by SIGTRAP TRAP_PERF does have the potential to cause
regressions in existing userspace.

While we still have time before userspace starts using and depending on
the new definition siginfo for SIGTRAP TRAP_PERF this set of changes
cleans up siginfo_t.

- The si_trapno field is demoted from magic alpha and sparc status and
  made an ordinary union member of the _sigfault member of siginfo_t.
  Without moving it of course.

- si_perf is replaced with si_perf_data and si_perf_type ending the
  abuse of si_errno.

- Unnecessary additions to signalfd_siginfo are removed.

v4: https://lkml.kernel.org/r/m1a6ot5e2h.fsf_-_@fess.ebiederm.org
v3: https://lkml.kernel.org/r/m1tuni8ano.fsf_-_@fess.ebiederm.org
v2: https://lkml.kernel.org/r/m14kfjh8et.fsf_-_@fess.ebiederm.org
v1: https://lkml.kernel.org/r/m1zgxfs7zq.fsf_-_@fess.ebiederm.org

This version drops the tests and fine grained handling of si_trapno
on alpha and sparc (replaced assuming si_trapno is valid for
all but the faults that defined different data).

Hopefully this is enough to not be scary as a fix for the ABI issues.

Tested-by: Marco Elver <elver@...gle.com>

Eric W. Biederman (5):
      siginfo: Move si_trapno inside the union inside _si_fault
      signal: Implement SIL_FAULT_TRAPNO
      signal: Factor force_sig_perf out of perf_sigtrap
      signal: Deliver all of the siginfo perf data in _perf
      signalfd: Remove SIL_PERF_EVENT fields from signalfd_siginfo


 arch/m68k/kernel/signal.c                          |  3 +-
 arch/x86/kernel/signal_compat.c                    |  9 +++-
 fs/signalfd.c                                      | 23 ++++-----
 include/linux/compat.h                             | 10 ++--
 include/linux/sched/signal.h                       |  1 +
 include/linux/signal.h                             |  1 +
 include/uapi/asm-generic/siginfo.h                 | 15 +++---
 include/uapi/linux/perf_event.h                    |  2 +-
 include/uapi/linux/signalfd.h                      |  4 +-
 kernel/events/core.c                               | 11 +---
 kernel/signal.c                                    | 59 +++++++++++++---------
 .../selftests/perf_events/sigtrap_threads.c        | 14 ++---
 12 files changed, 79 insertions(+), 73 deletions(-)

Eric