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From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Piotr Figiel <figiel@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	paulmck <paulmck@kernel.org>, Boqun Feng <boqun.feng@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>,
	"Dmitry V. Levin" <ldv@altlinux.org>,
	Florian Weimer <fweimer@redhat.com>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Andrei Vagin <avagin@gmail.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Peter Oskolkov <posk@google.com>,
	Kamil Yurtsever <kyurtsever@google.com>,
	Chris Kennelly <ckennelly@google.com>,
	Paul Turner <pjt@google.com>, emmir <emmir@google.com>,
	linux-man <linux-man@vger.kernel.org>,
	linux-api <linux-api@vger.kernel.org>
Subject: Re: [PATCH v2] ptrace: add PTRACE_GET_RSEQ_CONFIGURATION request
Date: Wed, 3 Mar 2021 13:55:39 -0500 (EST)	[thread overview]
Message-ID: <1647666880.9529.1614797739047.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <YDkchUnCe5ctDwYB@google.com>

----- On Feb 26, 2021, at 11:06 AM, Piotr Figiel figiel@google.com wrote:

> Hi,
> 
> On Fri, Feb 26, 2021 at 10:32:35AM -0500, Mathieu Desnoyers wrote:
>> > +static long ptrace_get_rseq_configuration(struct task_struct *task,
>> > +					  unsigned long size, void __user *data)
>> > +{
>> > +	struct ptrace_rseq_configuration conf = {
>> > +		.rseq_abi_pointer = (u64)(uintptr_t)task->rseq,
>> > +		.rseq_abi_size = sizeof(*task->rseq),
>> > +		.signature = task->rseq_sig,
>> > +		.flags = 0,
>> > +	};
>> > +
>> > +	size = min_t(unsigned long, size, sizeof(conf));
>> > +	if (copy_to_user(data, &conf, size))
>> > +		return -EFAULT;
>> > +	return sizeof(conf);
>> > +}
>> 
>> I think what Florian was after would be:
>> 
>> struct ptrace_rseq_configuration {
>> 	__u32 size;  /* size of struct ptrace_rseq_configuration */
>> 	__u32 flags;
>> 	__u64 rseq_abi_pointer;
>> 	__u32 signature;
>> 	__u32 pad;
>> };
>> 
>> where:
>> 
>>     .size = sizeof(struct ptrace_rseq_configuration),
>> 
>> This way, the configuration structure can be expanded in the future. The
>> rseq ABI structure is by definition fixed-size, so there is no point in
>> having its size here.
> 
> Still rseq syscall accepts the rseq ABI structure size as a paremeter.
> I think this way the information returned from ptrace is consistent with
> the userspace view of the rseq state and allows expansion in case the
> ABI structure would have to be extended (in spite of it's current
> definition).
> 
> The configuration structure still can be expanded as its size is
> reported to userspace as return value from the request (in line with
> Dmitry's comments).

Fair enough. And now with the reply from Florian I see that I misunderstood his
point.

Thanks,

Mathieu

> 
> Best regards, Piotr.

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

  reply	other threads:[~2021-03-03 20:59 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-26 13:51 [PATCH v2] ptrace: add PTRACE_GET_RSEQ_CONFIGURATION request Piotr Figiel
2021-02-26 15:32 ` Mathieu Desnoyers
2021-02-26 16:04   ` Michał Mirosław
2021-02-26 16:41     ` Mathieu Desnoyers
2021-02-26 16:06   ` Piotr Figiel
2021-03-03 18:55     ` Mathieu Desnoyers [this message]
2021-03-03 17:10   ` Florian Weimer
2021-03-10 18:50 ` Oleg Nesterov
2021-03-11 14:51 ` Mathieu Desnoyers
2021-03-11 16:51   ` Peter Zijlstra
2021-03-11 17:24     ` Mathieu Desnoyers
2021-03-17 13:13 ` [tip: sched/core] rseq, ptrace: Add " tip-bot2 for Piotr Figiel
2021-03-17 15:19 ` tip-bot2 for Piotr Figiel

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