linux-kernel - Re: [PATCH v4 0/5] siginfo: ABI fixes for TRAP

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Date:   Mon, 17 May 2021 22:53:20 +0200
From:   Marco Elver <elver@...gle.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
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>
Subject: Re: [PATCH v4 0/5] siginfo: ABI fixes for TRAP_PERF

On Mon, 17 May 2021 at 21:58, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> 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.
>
> 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).

And just to clarify, the rest of the series (including static-asserts)
for the next merge-window will be sent once this series is all sorted,
correct?

> 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

Looks good, thank you! I build-tested (defconfig -- x86_64, i386, arm,
arm64, m68k, sparc, alpha) this series together with a local patch to
pull in the static asserts from v3. Also re-ran perf_events kselftests
on x86_64 (native and 32bit compat).

Thanks,
-- Marco