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From: Carlos O'Donell <codonell@redhat.com>
To: Tulio Magno Quites Machado Filho <tuliom@ascii.art.br>,
	Florian Weimer <fweimer@redhat.com>,
	Michael Meissner <meissner@linux.ibm.com>,
	Alan Modra <amodra@gmail.com>,
	Peter Bergner <bergner@vnet.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Paul Burton <paul.burton@mips.com>,
	Will Deacon <will.deacon@arm.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Russell King <linux@armlinux.org.uk>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>, carlos <carlos@redhat.com>,
	Joseph Myers <joseph@codesourcery.com>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	libc-alpha <libc-alpha@sourceware.org>,
	Thomas Gleixner <tglx@linutronix.de>, Ben Maurer <bmaurer@fb.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Dave Watson <davejwatson@fb.com>, Paul Turner <pjt@google.com>,
	Rich Felker <dalias@libc.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-api <linux-api@vger.kernel.org>
Subject: Re: [PATCH 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v7)
Date: Mon, 8 Apr 2019 17:45:41 -0400	[thread overview]
Message-ID: <ce9fbc66-5eb9-0fa9-99fa-5abfe00ddfc2@redhat.com> (raw)
In-Reply-To: <877ec4pam2.fsf@linux.ibm.com>

On 4/8/19 3:20 PM, Tulio Magno Quites Machado Filho wrote:
> Carlos O'Donell <codonell@redhat.com> writes:
> 
>> On 4/5/19 5:16 AM, Florian Weimer wrote:
>>> * Carlos O'Donell:
>>>> It is valuable that it be a trap, particularly for constant pools because
>>>> it means that a jump into the constant pool will trap.
>>>
>>> Sorry, I don't understand why this matters in this context.  Would you
>>> please elaborate?
>>
>> Sorry, I wasn't very clear.
>>
>> My point is only that any accidental jumps, either with off-by-one (like you
>> fixed in gcc/glibc's signal unwinding most recently), result in a process fault
>> rather than executing RSEQ_SIG as a valid instruction *and then* continuing
>> onwards to the handler.
>>
>> A process fault is achieved either by a trap, or an invalid instruction, or
>> a privileged insn (like suggested for MIPS in this thread).
> 
> In that case, mtmsr (Move to Machine State Register) seems a good candidate.
> 
> mtmsr is available both on 32 and 64 bits since their first implementations.
> 
> It's a privileged instruction and should never appear in userspace
> code (causes SIGILL).
> 
> Any comments?
  
That seems good to me.

Mathieu,

What's required to move this forward for POWER?

-- 
Cheers,
Carlos.

WARNING: multiple messages have this Message-ID (diff)
From: Carlos O'Donell <codonell@redhat.com>
To: Tulio Magno Quites Machado Filho <tuliom@ascii.art.br>,
	Florian Weimer <fweimer@redhat.com>,
	Michael Meissner <meissner@linux.ibm.com>,
	Alan Modra <amodra@gmail.com>,
	Peter Bergner <bergner@vnet.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Paul Burton <paul.burton@mips.com>,
	Will Deacon <will.deacon@arm.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Russell King <linux@armlinux.org.uk>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>, carlos <carlos@redhat.com>,
	Joseph Myers <joseph@codesourcery.com>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	libc-alpha <libc-alpha@sourceware.org>,
	Thomas Gleixner <tglx@linutronix.de>, Ben Maurer <bmaurer@fb.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Dave Watson <davejwatson@fb.com>, Paul Turner <pjt@google.com>,
	Rich Felker <dalias@libc.org>l
Subject: Re: [PATCH 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v7)
Date: Mon, 8 Apr 2019 17:45:41 -0400	[thread overview]
Message-ID: <ce9fbc66-5eb9-0fa9-99fa-5abfe00ddfc2@redhat.com> (raw)
In-Reply-To: <877ec4pam2.fsf@linux.ibm.com>

On 4/8/19 3:20 PM, Tulio Magno Quites Machado Filho wrote:
> Carlos O'Donell <codonell@redhat.com> writes:
> 
>> On 4/5/19 5:16 AM, Florian Weimer wrote:
>>> * Carlos O'Donell:
>>>> It is valuable that it be a trap, particularly for constant pools because
>>>> it means that a jump into the constant pool will trap.
>>>
>>> Sorry, I don't understand why this matters in this context.  Would you
>>> please elaborate?
>>
>> Sorry, I wasn't very clear.
>>
>> My point is only that any accidental jumps, either with off-by-one (like you
>> fixed in gcc/glibc's signal unwinding most recently), result in a process fault
>> rather than executing RSEQ_SIG as a valid instruction *and then* continuing
>> onwards to the handler.
>>
>> A process fault is achieved either by a trap, or an invalid instruction, or
>> a privileged insn (like suggested for MIPS in this thread).
> 
> In that case, mtmsr (Move to Machine State Register) seems a good candidate.
> 
> mtmsr is available both on 32 and 64 bits since their first implementations.
> 
> It's a privileged instruction and should never appear in userspace
> code (causes SIGILL).
> 
> Any comments?
  
That seems good to me.

Mathieu,

What's required to move this forward for POWER?

-- 
Cheers,
Carlos.

  reply	other threads:[~2019-04-08 21:45 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20190212194253.1951-1-mathieu.desnoyers@efficios.com>
2019-02-12 19:42 ` [PATCH 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v7) Mathieu Desnoyers
2019-03-22 20:09   ` Carlos O'Donell
2019-03-25 15:54     ` Mathieu Desnoyers
2019-03-27  9:16       ` Martin Schwidefsky
2019-03-27  9:16         ` Martin Schwidefsky
2019-03-27 20:01         ` Mathieu Desnoyers
2019-03-27 20:01           ` Mathieu Desnoyers
2019-03-27 20:38         ` Carlos O'Donell
2019-03-27 20:38           ` Carlos O'Donell
2019-03-28  7:49           ` Martin Schwidefsky
2019-03-28  7:49             ` Martin Schwidefsky
2019-03-28 15:42             ` Mathieu Desnoyers
2019-03-28 15:42               ` Mathieu Desnoyers
2019-04-02  6:02       ` Michael Ellerman
2019-04-02  7:08         ` Florian Weimer
2019-04-02  7:08           ` Florian Weimer
2019-04-04 20:32           ` Carlos O'Donell
2019-04-04 20:32             ` Carlos O'Donell
2019-04-05  9:16             ` Florian Weimer
2019-04-05  9:16               ` Florian Weimer
2019-04-05 15:40               ` Carlos O'Donell
2019-04-05 15:40                 ` Carlos O'Donell
2019-04-08 19:20                 ` Tulio Magno Quites Machado Filho
2019-04-08 19:20                   ` Tulio Magno Quites Machado Filho
2019-04-08 21:45                   ` Carlos O'Donell [this message]
2019-04-08 21:45                     ` Carlos O'Donell
2019-04-09  4:23                     ` Michael Ellerman
2019-04-09  4:23                       ` Michael Ellerman
2019-04-09  9:29                       ` Alan Modra
2019-04-09  9:29                         ` Alan Modra
2019-04-09 13:58                         ` Tulio Magno Quites Machado Filho
2019-04-09 14:13                           ` Carlos O'Donell
2019-04-09 14:13                             ` Carlos O'Donell
2019-04-09 15:45                             ` Mathieu Desnoyers
2019-04-09 15:45                               ` Mathieu Desnoyers
2019-04-18 15:31                         ` Mathieu Desnoyers
2019-04-18 15:31                           ` Mathieu Desnoyers
2019-04-09 16:33                     ` Mathieu Desnoyers
2019-04-09 16:33                       ` Mathieu Desnoyers
2019-04-04 20:15         ` Carlos O'Donell
2019-04-04 20:50       ` Carlos O'Donell
2019-04-04 21:41         ` Paul Burton
2019-04-04 21:41           ` Paul Burton
2019-04-09 16:40           ` Mathieu Desnoyers
2019-04-09 16:40             ` Mathieu Desnoyers
2019-04-18 18:58           ` Mathieu Desnoyers
2019-04-18 18:58             ` Mathieu Desnoyers
2019-04-24 15:05             ` Mathieu Desnoyers
2019-04-24 15:05               ` Mathieu Desnoyers
2019-04-24 23:13               ` Paul Burton
2019-04-24 23:13                 ` Paul Burton
2019-04-25  0:41                 ` Maciej W. Rozycki
2019-04-25  0:41                   ` Maciej W. Rozycki
2019-02-12 19:42 ` [PATCH 2/4] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux Mathieu Desnoyers
2019-03-22 20:13   ` Carlos O'Donell

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