From: Boqun Feng <boqun.feng@gmail.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Will Deacon <will.deacon@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Andy Lutomirski <luto@amacapital.net>,
Dave Watson <davejwatson@fb.com>,
"linux-kernel" <linux-kernel@vger.kernel.org>,
"linux-api" <linux-api@vger.kernel.org>,
Paul Turner <pjt@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Russell King <linux@arm.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Andrew Hunter <ahh@google.com>, Andi Kleen <andi@firstfloor.org>,
Chris Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>,
rostedt <rostedt@goodmis.org>,
Josh Triplett <josh@joshtriplett.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Joel Fernandes <joelaf@google.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
"linuxppc-dev" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH 07/14] powerpc: Add support for restartable sequences
Date: Fri, 18 May 2018 07:50:43 +0800 [thread overview]
Message-ID: <1526601043.1338308.1376191416.0444B8C5@webmail.messagingengine.com> (raw)
In-Reply-To: <277374719.2144.1526570889798.JavaMail.zimbra@efficios.com>
On Thu, May 17, 2018, at 11:28 PM, Mathieu Desnoyers wrote:
> ----- On May 16, 2018, at 9:19 PM, Boqun Feng boqun.feng@gmail.com wrote:
>
> > On Wed, May 16, 2018 at 04:13:16PM -0400, Mathieu Desnoyers wrote:
> >> ----- On May 16, 2018, at 12:18 PM, Peter Zijlstra peterz@infradead.org wrote:
> >>
> >> > On Mon, Apr 30, 2018 at 06:44:26PM -0400, Mathieu Desnoyers wrote:
> >> >> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> >> >> index c32a181a7cbb..ed21a777e8c6 100644
> >> >> --- a/arch/powerpc/Kconfig
> >> >> +++ b/arch/powerpc/Kconfig
> >> >> @@ -223,6 +223,7 @@ config PPC
> >> >> select HAVE_SYSCALL_TRACEPOINTS
> >> >> select HAVE_VIRT_CPU_ACCOUNTING
> >> >> select HAVE_IRQ_TIME_ACCOUNTING
> >> >> + select HAVE_RSEQ
> >> >> select IRQ_DOMAIN
> >> >> select IRQ_FORCED_THREADING
> >> >> select MODULES_USE_ELF_RELA
> >> >> diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
> >> >> index 61db86ecd318..d3bb3aaaf5ac 100644
> >> >> --- a/arch/powerpc/kernel/signal.c
> >> >> +++ b/arch/powerpc/kernel/signal.c
> >> >> @@ -133,6 +133,8 @@ static void do_signal(struct task_struct *tsk)
> >> >> /* Re-enable the breakpoints for the signal stack */
> >> >> thread_change_pc(tsk, tsk->thread.regs);
> >> >>
> >> >> + rseq_signal_deliver(tsk->thread.regs);
> >> >> +
> >> >> if (is32) {
> >> >> if (ksig.ka.sa.sa_flags & SA_SIGINFO)
> >> >> ret = handle_rt_signal32(&ksig, oldset, tsk);
> >> >> @@ -164,6 +166,7 @@ void do_notify_resume(struct pt_regs *regs, unsigned long
> >> >> thread_info_flags)
> >> >> if (thread_info_flags & _TIF_NOTIFY_RESUME) {
> >> >> clear_thread_flag(TIF_NOTIFY_RESUME);
> >> >> tracehook_notify_resume(regs);
> >> >> + rseq_handle_notify_resume(regs);
> >> >> }
> >> >>
> >> >> user_enter();
> >> >
> >> > Again no rseq_syscall().
> >>
> >> Same question for PowerPC as for ARM:
> >>
> >> Considering that rseq_syscall is implemented as follows:
> >>
> >> +void rseq_syscall(struct pt_regs *regs)
> >> +{
> >> + unsigned long ip = instruction_pointer(regs);
> >> + struct task_struct *t = current;
> >> + struct rseq_cs rseq_cs;
> >> +
> >> + if (!t->rseq)
> >> + return;
> >> + if (!access_ok(VERIFY_READ, t->rseq, sizeof(*t->rseq)) ||
> >> + rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs))
> >> + force_sig(SIGSEGV, t);
> >> +}
> >>
> >> and that x86 calls it from syscall_return_slowpath() (which AFAIU is
> >> now used in the fast-path since KPTI), I wonder where we should call
> >
> > So we actually detect this after the syscall takes effect, right? I
> > wonder whether this could be problematic, because "disallowing syscall"
> > in rseq areas may means the syscall won't take effect to some people, I
> > guess?
> >
> >> this on PowerPC ? I was under the impression that PowerPC return to
> >> userspace fast-path was not calling C code unless work flags were set,
> >> but I might be wrong.
> >>
> >
> > I think you're right. So we have to introduce callsite to rseq_syscall()
> > in syscall path, something like:
> >
> > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> > index 51695608c68b..a25734a96640 100644
> > --- a/arch/powerpc/kernel/entry_64.S
> > +++ b/arch/powerpc/kernel/entry_64.S
> > @@ -222,6 +222,9 @@ system_call_exit:
> > mtmsrd r11,1
> > #endif /* CONFIG_PPC_BOOK3E */
> >
> > + addi r3,r1,STACK_FRAME_OVERHEAD
> > + bl rseq_syscall
> > +
> > ld r9,TI_FLAGS(r12)
> > li r11,-MAX_ERRNO
> > andi.
> > r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
> >
> > But I think it's important for us to first decide where (before or after
> > the syscall) we do the detection.
>
> As Peter said, we don't really care whether it's on syscall entry or
> exit, as
> long as the process gets killed when the erroneous use is detected. I
> think doing
> it on syscall exit is a bit easier because we can clearly access the
> userspace
> TLS, which AFAIU may be less straightforward on syscall entry.
>
Fair enough.
> We may want to add #ifdef CONFIG_DEBUG_RSEQ / #endif around the code you
> proposed above, so it's only compiled in if CONFIG_DEBUG_RSEQ=y.
>
OK.
> On the ARM leg of the email thread, Will Deacon suggests to test whether
> current->rseq
> is non-NULL before calling rseq_syscall(). I wonder if this added check
> is justified
> as the assembly level, considering that this is just a debugging option.
> We already do
> that check at the very beginning of rseq_syscall().
>
Yes, I think it's better to do the check in rseq_syscall(), leaving the asm
code a bit cleaner.
Regards,
Boqun
> Thoughts ?
>
> Thanks,
>
> Mathieu
>
> >
> > Regards,
> > Boqun
> >
> >> Thoughts ?
> >>
> >> Thanks!
> >>
> >> Mathieu
> >>
> >> --
> >> Mathieu Desnoyers
> >> EfficiOS Inc.
> > > http://www.efficios.com
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
next prev parent reply other threads:[~2018-05-17 23:50 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-30 22:44 [RFC PATCH for 4.18 00/14] Restartable Sequences Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 01/14] uapi headers: Provide types_32_64.h (v2) Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 02/14] rseq: Introduce restartable sequences system call (v13) Mathieu Desnoyers
2018-05-16 16:24 ` Peter Zijlstra
2018-05-16 20:18 ` Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 03/14] arm: Add restartable sequences support Mathieu Desnoyers
2018-05-16 16:18 ` Peter Zijlstra
2018-05-16 20:13 ` Mathieu Desnoyers
2018-05-17 13:32 ` Will Deacon
2018-05-17 15:30 ` Mathieu Desnoyers
2018-05-22 18:19 ` Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 04/14] arm: Wire up restartable sequences system call Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 05/14] x86: Add support for restartable sequences (v2) Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 06/14] x86: Wire up restartable sequence system call Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 07/14] powerpc: Add support for restartable sequences Mathieu Desnoyers
2018-05-16 16:18 ` Peter Zijlstra
2018-05-16 20:13 ` Mathieu Desnoyers
2018-05-17 1:19 ` Boqun Feng
2018-05-17 7:43 ` Peter Zijlstra
2018-05-17 15:28 ` Mathieu Desnoyers
2018-05-17 23:50 ` Boqun Feng [this message]
2018-05-18 18:17 ` Mathieu Desnoyers
2018-05-20 14:08 ` Boqun Feng
2018-05-23 20:14 ` Mathieu Desnoyers
2018-05-23 20:46 ` Paul E. McKenney
2018-05-23 21:29 ` Mathieu Desnoyers
2018-05-24 1:03 ` Michael Ellerman
2018-05-28 7:00 ` Mathieu Desnoyers
2018-05-18 12:38 ` Michael Ellerman
2018-04-30 22:44 ` [PATCH 08/14] powerpc: Wire up restartable sequences system call Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 09/14] selftests: lib.mk: Introduce OVERRIDE_TARGETS Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 10/14] rseq: selftests: Provide rseq library (v5) Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 11/14] rseq: selftests: Provide basic test Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 12/14] rseq: selftests: Provide basic percpu ops test (v2) Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 13/14] rseq: selftests: Provide parametrized tests (v2) Mathieu Desnoyers
2018-04-30 22:44 ` [PATCH 14/14] rseq: selftests: Provide Makefile, scripts, gitignore (v2) Mathieu Desnoyers
2018-05-02 3:53 ` [RFC PATCH for 4.18 00/14] Restartable Sequences Daniel Colascione
2018-05-02 8:43 ` Peter Zijlstra
2018-05-02 16:03 ` Mathieu Desnoyers
2018-05-02 16:07 ` Daniel Colascione
2018-05-02 16:42 ` Steven Rostedt
2018-05-02 16:55 ` Daniel Colascione
2018-05-03 16:12 ` Mathieu Desnoyers
2018-05-03 16:22 ` Daniel Colascione
2018-05-03 18:04 ` Mathieu Desnoyers
2018-05-03 16:48 ` Joel Fernandes
2018-05-03 17:18 ` Daniel Colascione
2018-05-03 17:46 ` Joel Fernandes
2018-05-04 22:17 ` Ben Maurer
2018-05-02 17:22 ` Peter Zijlstra
2018-05-02 18:27 ` Daniel Colascione
2018-05-02 20:22 ` Peter Zijlstra
2018-05-02 20:37 ` Daniel Colascione
2018-05-03 1:15 ` Steven Rostedt
2018-05-03 8:49 ` Peter Zijlstra
2018-05-06 10:03 ` Thomas Gleixner
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