linux-kernel - Re: [PATCH 08/12] add trace events for each syscall entry/exit

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Date:	Wed, 26 Aug 2009 09:47:36 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, laijs@...fujitsu.com, rostedt@...dmis.org,
	peterz@...radead.org, mathieu.desnoyers@...ymtl.ca,
	jiayingz@...gle.com, mbligh@...gle.com, lizf@...fujitsu.com
Subject: Re: [PATCH 08/12] add trace events for each syscall entry/exit

On Wed, Aug 26, 2009 at 12:09:01AM +0200, Frederic Weisbecker wrote:
> On Tue, Aug 25, 2009 at 11:40:21PM +0200, Frederic Weisbecker wrote:
> > On Tue, Aug 25, 2009 at 02:50:27PM +0200, Hendrik Brueckner wrote:
> > > Most arch syscall_get_nr() implementations returns -1 if the syscall
> > > number is not valid.  Accessing the bit field without a check might
> > > result in a kernel oops (at least I saw it on s390 for ftrace selftest).
> > > 
> > > Before this change, this problem did not occur, because the invalid
> > > syscall number (-1) caused syscall_nr_to_meta() to return NULL.
> > > 
> > > There are at least two scenarios where syscall_get_nr() can return -1:
> > > 
> > > 1. For example, ptrace stores an invalid syscall number, and thus,
> > >    tracing code resets it.
> > >    (see do_syscall_trace_enter in arch/s390/kernel/ptrace.c)
> > > 
> > > 2. The syscall_regfunc() (kernel/tracepoint.c) sets the TIF_SYSCALL_FTRACE
> > >    (now: TIF_SYSCALL_TRACEPOINT) flag for all threads which includes
> > >    kernel threads.
> > >    However, the ftrace selftest triggers a kernel oops when testing syscall
> > >    trace points:
> > >       - The kernel thread is started as ususal (do_fork()),
> > >       - tracing code sets TIF_SYSCALL_FTRACE,
> > >       - the ret_from_fork() function is triggered and starts
> > > 	ftrace_syscall_exit() with an invalid syscall number.
> > > 
> > > To avoid these scenarios, I suggest to check the syscall_nr.
> > > 
> > > [...]
> > > 
> > > Signed-off-by: Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
> > 
> > 
> > 
> > I'm queueing this one for .32
> > 
> > Thanks.
> 
> Btw it would be nice to have an ack from s390 maintainers.
> Martin, Heiko, no problem with this patch?

Acked-by: Heiko Carstens <heiko.carstens@...ibm.com>
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