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

Frederic Weisbecker
2009-08-25T22:09:06Z

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@linux.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?