linux-kernel - Re: Possible race between PTRACE_SETVFPREGS and PTRACE

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Message-ID: <20160531141817.GW19428@n2100.arm.linux.org.uk>
Date:	Tue, 31 May 2016 15:18:17 +0100
From:	Russell King - ARM Linux <linux@...linux.org.uk>
To:	Will Deacon <will.deacon@....com>
Cc:	Simon Marchi <simon.marchi@...csson.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: Possible race between PTRACE_SETVFPREGS and PTRACE_CONT on ARM?

On Tue, May 31, 2016 at 02:52:52PM +0100, Will Deacon wrote:
> The only thing I'm uncertain of is whether or not PTRACE_SEIZE/PTRACE_LISTEN
> allow switching to the child (but even then, how is the parent doing
> to issue such a request?).

I can't see how that would be possible - the parent needs to finish
the vfp_set() call before it can issue any others - and there can
only be one tracer.  IOW, if we're in vfp_set(), the thread must
have attached to the child, at which point PTRACE_SEIZE will be
rejected.

PTRACE_LISTEN also requires the child to be in STOP state as well, and
again, can only be issued from the current tracer.

-- 
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