From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman)
To: Linus Torvalds
<torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Cc: "linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
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Subject: Re: [PATCH 7/7] signal: Remove kernel interal si_code magic
Date: Tue, 18 Jul 2017 12:27:26 -0500 [thread overview]
Message-ID: <878tjlbqpt.fsf@xmission.com> (raw)
In-Reply-To: <CA+55aFyKsmf+BpYjcH30MGpHTDJ=zgYPx6kwyEB9CXXFxj_xsw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> (Linus Torvalds's message of "Tue, 18 Jul 2017 09:57:09 -0700")
Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org> writes:
> On Tue, Jul 18, 2017 at 7:06 AM, Eric W. Biederman
> <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> wrote:
>> struct siginfo is a union and the kernel since 2.4 has been hiding a union
>> tag in the high 16bits of si_code using the values:
>> __SI_KILL
>> __SI_TIMER
>> __SI_POLL
>> __SI_FAULT
>> __SI_CHLD
>> __SI_RT
>> __SI_MESGQ
>> __SI_SYS
>>
>> While this looks plausible on the surface, in practice this situation has
>> not worked well.
>
> So on the whole I think we just need to do this, but the part I really
> hate about this series is still this the siginfo_layout() part.
>
> I can well believe that it is needed for the compat case. siginfo is a
> piece of crap crazy type, and re-ordering fields for compat is
> something we are always going to have to do.
>
> But for the native case, the *only* reason we do not just copy the
> siginfo as-is seems to be that it's just too big, due to other bad
> design decisions in siginfo ("let's make sure it's big enough by
> allocating 512 bytes for it).
>
> And afaik, absolutely nobody uses more than about 36 bytes of that
> 512-byte _sifields union (and that one use is SIGILL with three
> pointers and three integers and some padding.
>
> So why don't we just say "screw this idiotic layout crap, and just
> unconditionally copy that much smaller maximum of bytes"?
>
> Leave that layout thing purely for compat handling.
I completely agree.
> Yes, yes, there's a couple of small gotchas's:
>
> - "_sys_private" for posix timers, and it would have to be moved to
> the end of the structure so that it doesn't get copied.
I don't think we actually need _sys_private at all.
I think the best solution would involve embedding struct siginfo
into struct k_itimer (as we always allocate one). Then we can just
perform container_of on the siginfo and look at the k_itimer instead.
> - make sure those 36 bytes are cleared when allocating the siginfo
> (this should be trivial) so that we don't leak any other memory.
>
> But on the whole, it looks pretty straightforward to just get rid of
> those stupid layout things, and make them purely about compat stuff.
>
> Please?
>
> The si_code stuff clearly needs to be done regardless, so much of this
> patch series looks good to me. But if we're doign this cleanup, can't
> we please go that one extra step and get rid of the crazy "let's treat
> the union as different types", and just treat it as a largely opaque
> thing.
>
> Pretty please?
That is my next step.
I have started on it but it is a big additional patch. I have to insert
a bunch of memsets to ensure we are not copying unitialized stack
contents to userspace.
I have been convinced not to expect any performance issues:
- Worst case two reads from memory 60ns*2 = 120ns.
- 650ns time to send a signal.
- 350ns time to receive a signal.
So that is maybe a 10% change, and more likely lost completely
in the noise.
I intend to measure the performance change just copying it all to see if
I even need to optimize to just copy the needed 36 bytes.
The diffstat for introducing a clear_siginfo to ensure we have made
those memsets is huge so I am worried about introducing bugs along
the way or missing something.
arch/alpha/kernel/osf_sys.c | 1 +
arch/alpha/kernel/signal.c | 2 ++
arch/alpha/kernel/traps.c | 5 ++++
arch/alpha/mm/fault.c | 2 ++
arch/arc/kernel/traps.c | 14 ++++++----
arch/arc/mm/fault.c | 1 +
arch/arm/kernel/ptrace.c | 2 ++
arch/arm/kernel/swp_emulate.c | 1 +
arch/arm/kernel/traps.c | 5 ++++
arch/arm/mm/alignment.c | 1 +
arch/arm/mm/fault.c | 3 ++
arch/arm/vfp/vfpmodule.c | 2 +-
arch/arm64/kernel/debug-monitors.c | 13 +++++----
arch/arm64/kernel/fpsimd.c | 2 +-
arch/arm64/kernel/ptrace.c | 13 +++++----
arch/arm64/kernel/traps.c | 2 ++
arch/arm64/mm/fault.c | 4 +++
arch/blackfin/kernel/traps.c | 1 +
arch/c6x/kernel/traps.c | 1 +
arch/cris/mm/fault.c | 1 +
arch/frv/kernel/traps.c | 7 +++++
arch/frv/mm/fault.c | 1 +
arch/hexagon/kernel/traps.c | 1 +
arch/hexagon/mm/vm_fault.c | 2 ++
arch/ia64/kernel/brl_emu.c | 3 ++
arch/ia64/kernel/signal.c | 2 ++
arch/ia64/kernel/traps.c | 3 +-
arch/ia64/kernel/unaligned.c | 1 +
arch/ia64/mm/fault.c | 1 +
arch/m32r/kernel/traps.c | 1 +
arch/m32r/mm/fault.c | 1 +
arch/m68k/kernel/traps.c | 2 ++
arch/m68k/mm/fault.c | 3 +-
arch/metag/kernel/traps.c | 2 ++
arch/metag/mm/fault.c | 2 ++
arch/microblaze/kernel/exceptions.c | 1 +
arch/microblaze/mm/fault.c | 1 +
arch/mips/kernel/traps.c | 29 +++++++++++++------
arch/mips/mm/fault.c | 1 +
arch/mn10300/kernel/fpu.c | 1 +
arch/mn10300/kernel/traps.c | 1 +
arch/mn10300/mm/fault.c | 1 +
arch/mn10300/mm/misalignment.c | 2 ++
arch/nios2/kernel/traps.c | 1 +
arch/openrisc/kernel/traps.c | 5 +++-
arch/openrisc/mm/fault.c | 1 +
arch/parisc/kernel/ptrace.c | 1 +
arch/parisc/kernel/traps.c | 2 ++
arch/parisc/kernel/unaligned.c | 2 ++
arch/parisc/math-emu/driver.c | 1 +
arch/parisc/mm/fault.c | 1 +
arch/powerpc/kernel/process.c | 2 ++
arch/powerpc/kernel/traps.c | 4 +--
arch/powerpc/mm/fault.c | 1 +
arch/powerpc/platforms/cell/spufs/fault.c | 2 +-
arch/s390/kernel/traps.c | 3 ++
arch/s390/mm/fault.c | 2 ++
arch/score/kernel/traps.c | 1 +
arch/score/mm/fault.c | 1 +
arch/sh/kernel/hw_breakpoint.c | 1 +
arch/sh/kernel/traps_32.c | 4 +++
arch/sh/math-emu/math.c | 1 +
arch/sh/mm/fault.c | 1 +
arch/sparc/kernel/process_64.c | 1 +
arch/sparc/kernel/sys_sparc_32.c | 1 +
arch/sparc/kernel/sys_sparc_64.c | 1 +
arch/sparc/kernel/traps_32.c | 10 +++++++
arch/sparc/kernel/traps_64.c | 15 ++++++++++
arch/sparc/kernel/unaligned_32.c | 1 +
arch/sparc/mm/fault_32.c | 1 +
arch/sparc/mm/fault_64.c | 1 +
arch/tile/kernel/hardwall.c | 1 +
arch/tile/kernel/ptrace.c | 2 +-
arch/tile/kernel/single_step.c | 24 +++++++++-------
arch/tile/kernel/traps.c | 4 ++-
arch/tile/kernel/unaligned.c | 46 +++++++++++++++++--------------
arch/tile/mm/fault.c | 1 +
arch/um/kernel/ptrace.c | 2 +-
arch/um/kernel/trap.c | 4 ++-
arch/unicore32/kernel/fpu-ucf64.c | 3 +-
arch/unicore32/mm/fault.c | 3 ++
arch/x86/entry/vsyscall/vsyscall_64.c | 2 +-
arch/x86/kernel/ptrace.c | 2 +-
arch/x86/kernel/traps.c | 3 ++
arch/x86/kvm/mmu.c | 1 +
arch/x86/mm/fault.c | 1 +
arch/xtensa/kernel/ptrace.c | 1 +
arch/xtensa/kernel/traps.c | 1 +
arch/xtensa/mm/fault.c | 1 +
drivers/usb/core/devio.c | 4 +--
fs/fcntl.c | 1 +
include/linux/ptrace.h | 2 +-
include/linux/signal.h | 5 ++++
ipc/mqueue.c | 1 +
kernel/debug/kdb/kdb_main.c | 1 +
kernel/ptrace.c | 2 +-
kernel/seccomp.c | 2 +-
kernel/signal.c | 21 ++++++++++----
kernel/time/posix-timers.c | 2 +-
mm/memory-failure.c | 1 +
100 files changed, 272 insertions(+), 85 deletions(-)
Eric
next prev parent reply other threads:[~2017-07-18 17:27 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <87lgot2loq.fsf@xmission.com>
[not found] ` <87zid90vye.fsf_-_@xmission.com>
[not found] ` <20170615225426.GP31671@ZenIV.linux.org.uk>
[not found] ` <87poe4zrs1.fsf@xmission.com>
[not found] ` <CA+55aFxpv+gchzs7AYgSC8feAOV=B6mjFgBVm4Kx+83J2CNE-w@mail.gmail.com>
[not found] ` <87poe3vsa9.fsf@xmission.com>
[not found] ` <CALCETrX=SquyR8JZqHDNx=_FQKQo-0u9AxfdUwJs_hujVO2A-g@mail.gmail.com>
[not found] ` <87h8zfua59.fsf@xmission.com>
[not found] ` <CALCETrWPBn31Dye=81r2ZMainNOnDy5c_QxbU2uRjnJs0ie=Zg@mail.gmail.com>
[not found] ` <87r2yjsuwl.fsf@xmission.com>
[not found] ` <20170616191602.GA10675@1wt.eu>
2017-06-30 12:36 ` [PATCH 0/8] signal: Fix sending signals with siginfo Eric W. Biederman
2017-07-18 14:04 ` [PATCH v2 0/7] " Eric W. Biederman
2017-07-18 14:06 ` [PATCH 1/7] signal/alpha: Document a conflict with SI_USER for SIGTRAP Eric W. Biederman
[not found] ` <20170718140651.15973-1-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2017-07-18 18:22 ` Richard Henderson
2017-07-18 14:06 ` [PATCH 4/7] signal/mips: Document a conflict with SI_USER with SIGFPE Eric W. Biederman
2017-08-07 16:18 ` Maciej W. Rozycki
2017-08-07 17:41 ` Linus Torvalds
2017-08-07 19:55 ` Ralf Baechle
2017-08-08 15:29 ` Eric W. Biederman
2017-08-08 23:19 ` Maciej W. Rozycki
[not found] ` <87o9shg7t7.fsf_-_-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2017-07-18 14:06 ` [PATCH 2/7] signal/ia64: " Eric W. Biederman
2017-07-18 14:06 ` [PATCH 3/7] signal/sparc: " Eric W. Biederman
2017-07-18 14:06 ` [PATCH 5/7] signal/testing: Don't look for __SI_FAULT in userspace Eric W. Biederman
2017-07-18 14:06 ` [PATCH 6/7] fcntl: Don't use ambiguous SIG_POLL si_codes Eric W. Biederman
[not found] ` <20170718140651.15973-6-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2017-07-20 16:16 ` Oleg Nesterov
2017-07-21 2:33 ` Eric W. Biederman
2017-07-18 14:06 ` [PATCH 7/7] signal: Remove kernel interal si_code magic Eric W. Biederman
[not found] ` <20170718140651.15973-7-ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2017-07-18 16:57 ` Linus Torvalds
[not found] ` <CA+55aFyKsmf+BpYjcH30MGpHTDJ=zgYPx6kwyEB9CXXFxj_xsw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-07-18 17:27 ` Eric W. Biederman [this message]
[not found] ` <878tjlbqpt.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2017-07-22 20:25 ` Simplfying copy_siginfo_to_user Eric W. Biederman
[not found] ` <8760ek5ics.fsf_-_-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2017-07-24 17:43 ` Linus Torvalds
[not found] ` <CA+55aFyH5W2doo9vxXta_-pXfNXqQ19d7z48k1hmfAot+aJvMw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-07-24 19:01 ` Eric W. Biederman
2017-07-25 1:37 ` Al Viro
2017-07-31 16:37 ` Eric W. Biederman
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