linux-kernel - Re: [PATCH] tracing/syscalls: ignore numbers outside NR

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Message-ID: <20141030111441.GP27405@n2100.arm.linux.org.uk>
Date:	Thu, 30 Oct 2014 11:14:41 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Rabin Vincent <rabin@....in>,
	linux-arm-kernel@...ts.infradead.org,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing/syscalls: ignore numbers outside NR_syscalls'
 range

On Thu, Oct 30, 2014 at 07:10:39AM -0400, Steven Rostedt wrote:
> On Thu, 30 Oct 2014 10:18:08 +0000
> Russell King - ARM Linux <linux@....linux.org.uk> wrote:
> 
> > On Thu, Oct 30, 2014 at 01:26:06AM -0700, Christoph Hellwig wrote:
> > > On Wed, Oct 29, 2014 at 11:06:58PM +0100, Rabin Vincent wrote:
> > > > ARM has some private syscalls (for example, set_tls(2)) which lie
> > > > outside the range of NR_syscalls.  If any of these are called while
> > > > syscall tracing is being performed, out-of-bounds array access will
> > > > occur in the ftrace and perf sys_{enter,exit} handlers.
> > > 
> > > While this patch looks like good caution, having syscalls outside of
> > > NR_syscalls seems like a receipe for a disaster.  Can you try to fix
> > > that issue as ell, please?
> > 
> > No.  We've had them since the inception of Linux on ARM.  They predate
> > this tracing crap by more than a decade.  We're not changing them
> > because that would be a massive user API breakage.
> > 
> 
> Since syscall tracing is only broken on ARM, then the fix needs to be
> ARM specific, and not remove the check for all other architectures that
> have a sane NR_syscalls variable.

This issue came up before.

We have always had syscall number range of 0x900000 or so.  The tracing
design does not expect that.  Therefore, the tracing design did not take
account of ARM when it was created.  Therefore, it's up to the tracing
people to decide how to properly fit their ill-designed subsystem into
one of the popular and well-established kernel architectures - or at
least suggest a way to work around this issue.

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