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

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Date:	Wed, 26 Aug 2009 00:09:01 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
Cc:	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 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.
> > 
> > For instance, the ftrace selftest fails for s390 (with config option
> > CONFIG_FTRACE_SYSCALLS set) and produces the following kernel oops.
> > 
> > Unable to handle kernel pointer dereference at virtual kernel address 2000000000
> > 
> > Oops: 0038 [#1] PREEMPT SMP
> > Modules linked in:
> > CPU: 0 Not tainted 2.6.31-rc6-next-20090819-dirty #18
> > Process kthreadd (pid: 818, task: 000000003ea207e8, ksp: 000000003e813eb8)
> > Krnl PSW : 0704100180000000 00000000000ea54c (ftrace_syscall_exit+0x58/0xdc)
> >            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:0 CC:1 PM:0 EA:3
> > Krnl GPRS: 0000000000000000 00000000000e0000 ffffffffffffffff 20000000008c2650
> >            0000000000000007 0000000000000000 0000000000000000 0000000000000000
> >            0000000000000000 0000000000000000 ffffffffffffffff 000000003e813d78
> >            000000003e813f58 0000000000505ba8 000000003e813e18 000000003e813d78
> > Krnl Code: 00000000000ea540: e330d0000008       ag      %r3,0(%r13)
> >            00000000000ea546: a7480007           lhi     %r4,7
> >            00000000000ea54a: 1442               nr      %r4,%r2
> >           >00000000000ea54c: e31030000090       llgc    %r1,0(%r3)
> >            00000000000ea552: 5410d008           n       %r1,8(%r13)
> >            00000000000ea556: 8a104000           sra     %r1,0(%r4)
> >            00000000000ea55a: 5410d00c           n       %r1,12(%r13)
> >            00000000000ea55e: 1211               ltr     %r1,%r1
> > Call Trace:
> > ([<0000000000000000>] 0x0)
> >  [<000000000001fa22>] do_syscall_trace_exit+0x132/0x18c
> >  [<000000000002d0c4>] sysc_return+0x0/0x8
> >  [<000000000001c738>] kernel_thread_starter+0x0/0xc
> > Last Breaking-Event-Address:
> >  [<00000000000ea51e>] ftrace_syscall_exit+0x2a/0xdc
> > 
> > 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?

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