From: Marco Elver <elver@google.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
Florian Weimer <fweimer@redhat.com>,
"David S. Miller" <davem@davemloft.net>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Collingbourne <pcc@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
Alexander Potapenko <glider@google.com>,
sparclinux <sparclinux@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: siginfo_t ABI break on sparc64 from si_addr_lsb move 3y ago
Date: Sat, 1 May 2021 01:50:08 +0200 [thread overview]
Message-ID: <CANpmjNNU=00iq50xyVpqeg21kata+cTS=wZ7zcU_78K=rWL-=w@mail.gmail.com> (raw)
In-Reply-To: <m17dkjttpj.fsf@fess.ebiederm.org>
On Fri, 30 Apr 2021 at 22:15, Eric W. Biederman <ebiederm@xmission.com> wrote:
[...]
> arm64 only abuses si_errno in compat code for bug compatibility with
> arm32.
>
> > Given it'd be wasted space otherwise, and we define the semantics of
> > whatever is stored in siginfo on the new signal, it'd be good to keep.
>
> Except you don't completely. You are not defining a new signal. You
> are extending the definition of SIGTRAP. Anything generic that
> responds to all SIGTRAPs can reasonably be looking at si_errno.
I see where you're coming from, and agree with this if si_errno
already had some semantics for some subset of SIGTRAPs. I've tried to
analyze the situation a bit further, since siginfo seems to be a giant
minefield and semantics is underspecified at best. :-)
Do any of the existing SIGTRAPs define si_errno to be set? As far as I
can tell, they don't.
If this is true, I think there are benefits and downsides to
repurposing si_errno (similar to what SIGSYS did). The obvious
downside is as you suggest, it's not always a real errno. The benefit
is that we avoid introducing more and more fields -- i.e. if we permit
si_errno to be repurposed for SIGTRAP and its value depends on the
precise si_code, too, we simplify siginfo's overall definition (also
given every new field needs more code in kernel/signal.c, too).
Given SIGTRAPs are in response to some user-selected event in the
user's code (breakpoints, ptrace, etc. ... now perf events), the user
must already check the si_code to select the right action because
SIGTRAPs are not alike (unlike, e.g. SIGSEGV). Because of this, I
think that repurposing si_errno in an si_code-dependent way for
SIGTRAPs is safe.
If you think it is simply untenable to repurpose si_errno for
SIGTRAPs, please confirm -- I'll just send a minimal patch to fix (I'd
probably just remove setting it... everything else is too intrusive as
a "fix".. sigh).
The cleanups as you outline below seem orthogonal and not urgent for
5.13 (all changes and cleanups for __ARCH_SI_TRAPNO seem too intrusive
without -next exposure).
Thanks,
-- Marco
> Further you are already adding a field with si_perf you can just as
> easily add a second field with well defined semantics for that data.
>
> >> The code is only safe if the analysis that says we can move si_trapno
> >> and perhaps the ia64 fields into the union is correct. It looks like
> >> ia64 much more actively uses it's signal extension fields including for
> >> SIGTRAP, so I am not at all certain the generic definition of
> >> perf_sigtrap is safe on ia64.
> >
> > Trying to understand the requirements of si_trapno myself: safe here
> > would mean that si_trapno is not required if we fire our SIGTRAP /
> > TRAP_PERF.
> >
> > As far as I can tell that is the case -- see below.
> >
> >> > I suppose in theory sparc64 or alpha might start using the other
> >> > fields in the future, and an application might be compiled against
> >> > mismatched headers, but that is unlikely and is already broken
> >> > with the current headers.
> >>
> >> If we localize the use of si_trapno to just a few special cases on alpha
> >> and sparc I think we don't even need to worry about breaking userspace
> >> on any architecture. It will complicate siginfo_layout, but it is a
> >> complication that reflects reality.
> >>
> >> I don't have a clue how any of this affects ia64. Does perf work on
> >> ia64? Does perf work on sparc, and alpha?
> >>
> >> If perf works on ia64 we need to take a hard look at what is going on
> >> there as well.
> >
> > No perf on ia64, but it seems alpha and sparc have perf:
> >
> > $ git grep 'select.*HAVE_PERF_EVENTS$' -- arch/
> > arch/alpha/Kconfig: select HAVE_PERF_EVENTS <--
> > arch/arc/Kconfig: select HAVE_PERF_EVENTS
> > arch/arm/Kconfig: select HAVE_PERF_EVENTS
> > arch/arm64/Kconfig: select HAVE_PERF_EVENTS
> > arch/csky/Kconfig: select HAVE_PERF_EVENTS
> > arch/hexagon/Kconfig: select HAVE_PERF_EVENTS
> > arch/mips/Kconfig: select HAVE_PERF_EVENTS
> > arch/nds32/Kconfig: select HAVE_PERF_EVENTS
> > arch/parisc/Kconfig: select HAVE_PERF_EVENTS
> > arch/powerpc/Kconfig: select HAVE_PERF_EVENTS
> > arch/riscv/Kconfig: select HAVE_PERF_EVENTS
> > arch/s390/Kconfig: select HAVE_PERF_EVENTS
> > arch/sh/Kconfig: select HAVE_PERF_EVENTS
> > arch/sparc/Kconfig: select HAVE_PERF_EVENTS <--
> > arch/x86/Kconfig: select HAVE_PERF_EVENTS
> > arch/xtensa/Kconfig: select HAVE_PERF_EVENTS
> >
> > Now, given ia64 is not an issue, I wanted to understand the semantics of
> > si_trapno. Per https://man7.org/linux/man-pages/man2/sigaction.2.html, I
> > see:
> >
> > int si_trapno; /* Trap number that caused
> > hardware-generated signal
> > (unused on most architectures) */
> >
> > ... its intended semantics seem to suggest it would only be used by some
> > architecture-specific signal like you identified above. So if the
> > semantics is some code of a hardware trap/fault, then we're fine and do
> > not need to set it.
> >
> > Also bearing in mind we define the semantics any new signal, and given
> > most architectures do not have si_trapno, definitions of new generic
> > signals should probably not include odd architecture specific details
> > related to old architectures.
> >
> > From all this, my understanding now is that we can move si_trapno into
> > the union, correct? What else did you have in mind?
>
> Yes. Let's move si_trapno into the union.
>
> That implies a few things like siginfo_layout needs to change.
>
> The helpers in kernel/signal.c can change to not imply that
> if you define __ARCH_SI_TRAPNO you must always define and
> pass in si_trapno. A force_sig_trapno could be defined instead
> to handle the cases that alpha and sparc use si_trapno.
>
> It would be nice if a force_sig_perf_trap could be factored
> out of perf_trap and placed in kernel/signal.c.
>
> My experience (especially this round) is that it becomes much easier to
> audit the users of siginfo if there is a dedicated function in
> kernel/signal.c that is simply passed the parameters that need
> to be placed in siginfo.
>
> So I would very much like to see if I can make force_sig_info static.
>
> Eric
>
next prev parent reply other threads:[~2021-04-30 23:50 UTC|newest]
Thread overview: 118+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-29 7:48 siginfo_t ABI break on sparc64 from si_addr_lsb move 3y ago Marco Elver
2021-04-29 17:23 ` Eric W. Biederman
2021-04-29 18:46 ` Marco Elver
2021-04-29 20:48 ` Arnd Bergmann
2021-04-30 17:08 ` Eric W. Biederman
2021-04-30 19:07 ` Marco Elver
2021-04-30 20:15 ` Eric W. Biederman
2021-04-30 23:50 ` Marco Elver [this message]
2021-04-30 22:49 ` [RFC][PATCH 0/3] signal: Move si_trapno into the _si_fault union Eric W. Biederman
2021-04-30 22:50 ` [PATCH 1/3] siginfo: Move si_trapno inside the union inside _si_fault Eric W. Biederman
2021-05-01 10:31 ` Marco Elver
2021-05-02 18:27 ` Eric W. Biederman
2021-04-30 22:54 ` [PATCH 2/3] signal: Implement SIL_FAULT_TRAPNO Eric W. Biederman
2021-04-30 23:19 ` Eric W. Biederman
2021-05-01 10:33 ` Marco Elver
2021-05-02 18:24 ` Eric W. Biederman
2021-04-30 22:55 ` [PATCH 3/3] signal: Use dedicated helpers to send signals with si_trapno set Eric W. Biederman
2021-05-01 10:33 ` Marco Elver
2021-04-30 22:56 ` [PATCH 4/3] signal: Remove __ARCH_SI_TRAPNO Eric W. Biederman
2021-04-30 23:23 ` Is perf_sigtrap synchronous? Eric W. Biederman
2021-05-01 0:28 ` Marco Elver
2021-04-30 23:42 ` [PATCH 5/3] signal: Rename SIL_PERF_EVENT SIL_FAULT_PERF_EVENT for consistency Eric W. Biederman
2021-05-01 10:35 ` Marco Elver
2021-04-30 23:43 ` [PATCH 6/3] signal: Factor force_sig_perf out of perf_sigtrap Eric W. Biederman
2021-05-01 10:45 ` Marco Elver
2021-04-30 23:43 ` [PATCH 7/3] signal: Deliver all of the perf_data in si_perf Eric W. Biederman
2021-05-01 10:47 ` Marco Elver
2021-05-02 18:39 ` Eric W. Biederman
2021-05-02 19:13 ` Marco Elver
2021-05-03 12:44 ` Peter Zijlstra
2021-05-03 19:38 ` Eric W. Biederman
2021-05-03 19:53 ` Marco Elver
2021-04-30 23:47 ` [RFC][PATCH 0/3] signal: Move si_trapno into the _si_fault union Eric W. Biederman
2021-05-01 0:37 ` Marco Elver
2021-05-01 15:16 ` Eric W. Biederman
2021-05-01 16:24 ` Marco Elver
2021-05-03 20:25 ` [PATCH 00/12] signal: sort out si_trapno and si_perf Eric W. Biederman
2021-05-03 20:38 ` [PATCH 01/12] sparc64: Add compile-time asserts for siginfo_t offsets Eric W. Beiderman
2021-05-03 20:38 ` [PATCH 02/12] arm: " Eric W. Beiderman
2021-05-03 20:38 ` [PATCH 03/12] arm64: " Eric W. Beiderman
2021-05-03 20:38 ` [PATCH 04/12] siginfo: Move si_trapno inside the union inside _si_fault Eric W. Beiderman
2021-05-03 20:38 ` [PATCH 05/12] signal: Implement SIL_FAULT_TRAPNO Eric W. Beiderman
2021-05-03 20:38 ` [PATCH 06/12] signal: Use dedicated helpers to send signals with si_trapno set Eric W. Beiderman
2021-05-03 20:38 ` [PATCH 07/12] signal: Remove __ARCH_SI_TRAPNO Eric W. Beiderman
2021-05-03 20:38 ` [PATCH 08/12] signal: Rename SIL_PERF_EVENT SIL_FAULT_PERF_EVENT for consistency Eric W. Beiderman
2021-05-03 20:38 ` [PATCH 09/12] signal: Factor force_sig_perf out of perf_sigtrap Eric W. Beiderman
2021-05-03 20:38 ` [PATCH 10/12] signal: Redefine signinfo so 64bit fields are possible Eric W. Beiderman
2021-05-03 21:04 ` Eric W. Biederman
2021-05-03 22:47 ` Marco Elver
2021-05-04 3:42 ` Eric W. Biederman
2021-05-04 4:03 ` Peter Collingbourne
2021-05-04 9:52 ` Marco Elver
2021-05-04 16:16 ` Eric W. Biederman
2021-05-03 20:38 ` [PATCH 11/12] signal: Deliver all of the siginfo perf data in _perf Eric W. Beiderman
2021-05-03 20:38 ` [PATCH 12/12] signalfd: Remove SIL_FAULT_PERF_EVENT fields from signalfd_siginfo Eric W. Beiderman
2021-05-04 21:13 ` [PATCH v3 00/12] signal: sort out si_trapno and si_perf Eric W. Biederman
2021-05-04 22:05 ` Marco Elver
2021-05-05 14:12 ` Eric W. Biederman
2021-05-05 14:10 ` [PATCH v3 01/12] sparc64: Add compile-time asserts for siginfo_t offsets Eric W. Beiderman
2021-05-05 14:10 ` [PATCH v3 02/12] arm: " Eric W. Beiderman
2021-05-05 14:10 ` [PATCH v3 03/12] arm64: " Eric W. Beiderman
2021-05-05 14:10 ` [PATCH v3 04/12] signal: Verify the alignment and size of siginfo_t Eric W. Beiderman
2021-05-05 17:24 ` Marco Elver
2021-05-05 14:10 ` [PATCH v3 05/12] siginfo: Move si_trapno inside the union inside _si_fault Eric W. Beiderman
2021-05-05 14:10 ` [PATCH v3 06/12] signal: Implement SIL_FAULT_TRAPNO Eric W. Beiderman
2021-05-05 17:25 ` Marco Elver
2021-05-05 14:10 ` [PATCH v3 07/12] signal: Use dedicated helpers to send signals with si_trapno set Eric W. Beiderman
2021-05-05 17:25 ` Marco Elver
2021-05-05 14:10 ` [PATCH v3 08/12] signal: Remove __ARCH_SI_TRAPNO Eric W. Beiderman
2021-05-05 17:25 ` Marco Elver
2021-05-05 14:10 ` [PATCH v3 09/12] signal: Rename SIL_PERF_EVENT SIL_FAULT_PERF_EVENT for consistency Eric W. Beiderman
2021-05-05 17:26 ` Marco Elver
2021-05-05 14:10 ` [PATCH v3 10/12] signal: Factor force_sig_perf out of perf_sigtrap Eric W. Beiderman
2021-05-05 17:26 ` Marco Elver
2021-05-06 10:54 ` Peter Zijlstra
2021-05-05 14:11 ` [PATCH v3 11/12] signal: Deliver all of the siginfo perf data in _perf Eric W. Beiderman
2021-05-05 17:27 ` Marco Elver
2021-05-05 14:11 ` [PATCH v3 12/12] signalfd: Remove SIL_FAULT_PERF_EVENT fields from signalfd_siginfo Eric W. Beiderman
2021-05-05 17:27 ` Marco Elver
2021-05-05 17:28 ` [PATCH v3 00/12] signal: sort out si_trapno and si_perf Marco Elver
2021-05-06 7:00 ` Geert Uytterhoeven
2021-05-06 10:43 ` Marco Elver
2021-05-06 15:28 ` Eric W. Biederman
2021-05-06 15:14 ` Eric W. Biederman
2021-05-14 4:54 ` [GIT PULL] siginfo: ABI fixes for v5.13-rc2 Eric W. Biederman
2021-05-14 19:14 ` Linus Torvalds
2021-05-14 21:15 ` Eric W. Biederman
2021-05-14 22:38 ` Eric W. Biederman
2021-05-16 7:40 ` Ingo Molnar
2021-05-17 15:29 ` Eric W. Biederman
2021-05-21 14:59 ` [GIT PULL] siginfo: ABI fixes for v5.13-rc3 Eric W. Biederman
2021-05-21 16:34 ` pr-tracker-bot
2021-05-17 19:56 ` [PATCH v4 0/5] siginfo: ABI fixes for TRAP_PERF Eric W. Biederman
2021-05-17 19:57 ` [PATCH v4 1/5] siginfo: Move si_trapno inside the union inside _si_fault Eric W. Beiderman
2021-05-17 19:57 ` [PATCH v4 2/5] signal: Implement SIL_FAULT_TRAPNO Eric W. Beiderman
2021-05-17 19:57 ` [PATCH v4 3/5] signal: Factor force_sig_perf out of perf_sigtrap Eric W. Beiderman
2021-05-17 19:57 ` [PATCH v4 4/5] signal: Deliver all of the siginfo perf data in _perf Eric W. Beiderman
2021-05-17 19:57 ` [PATCH v4 5/5] signalfd: Remove SIL_PERF_EVENT fields from signalfd_siginfo Eric W. Beiderman
2021-05-17 20:53 ` [PATCH v4 0/5] siginfo: ABI fixes for TRAP_PERF Marco Elver
2021-05-18 3:46 ` Eric W. Biederman
2021-05-18 6:44 ` Marco Elver
2021-05-01 16:26 ` [RFC][PATCH 0/3] signal: Move si_trapno into the _si_fault union Marco Elver
2021-07-15 18:09 ` [PATCH 0/6] Final si_trapno bits Eric W. Biederman
2021-07-15 18:11 ` [PATCH 1/6] sparc64: Add compile-time asserts for siginfo_t offsets Eric W. Biederman
2021-07-15 18:11 ` [PATCH 2/6] arm: " Eric W. Biederman
2021-07-15 18:11 ` [PATCH 3/6] arm64: " Eric W. Biederman
2021-07-15 18:12 ` [PATCH 4/6] signal/sparc: si_trapno is only used with SIGILL ILL_ILLTRP Eric W. Biederman
2021-07-16 11:49 ` Marco Elver
2021-07-15 18:12 ` [PATCH 5/6] signal/alpha: si_trapno is only used with SIGFPE and SIGTRAP TRAP_UNK Eric W. Biederman
2021-07-16 11:48 ` Marco Elver
2021-07-15 18:13 ` [PATCH 6/6] signal: Remove the generic __ARCH_SI_TRAPNO support Eric W. Biederman
2021-07-16 11:48 ` Marco Elver
2021-07-16 11:50 ` [PATCH 0/6] Final si_trapno bits Marco Elver
2021-07-16 16:08 ` Eric W. Biederman
2021-07-16 17:15 ` Marco Elver
2021-07-16 16:06 ` [PATCH 7/7] signal: Verify the alignment and size of siginfo_t Eric W. Biederman
2021-07-16 16:07 ` [PATCH 8/6] signal: Rename SIL_PERF_EVENT SIL_FAULT_PERF_EVENT for consistency Eric W. Biederman
2021-04-30 20:43 ` siginfo_t ABI break on sparc64 from si_addr_lsb move 3y ago Arnd Bergmann
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