Messages in this thread Patch in this message | | | Date | Tue, 25 Aug 2009 14:50:27 +0200 | From | Hendrik Brueckner <> | Subject | Re: [PATCH 08/12] add trace events for each syscall entry/exit |
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On Mon, Aug 10, 2009 at 04:52:47PM -0400, Jason Baron wrote: > +void ftrace_syscall_enter(struct pt_regs *regs, long id) > { > struct syscall_trace_enter *entry; > struct syscall_metadata *sys_data; > @@ -150,6 +105,8 @@ void ftrace_syscall_enter(struct pt_regs *regs) > int syscall_nr; > > syscall_nr = syscall_get_nr(current, regs); > + if (!test_bit(syscall_nr, enabled_enter_syscalls)) > + return; > > sys_data = syscall_nr_to_meta(syscall_nr); > if (!sys_data)
> +void ftrace_syscall_exit(struct pt_regs *regs, long ret) > { > struct syscall_trace_exit *entry; > struct syscall_metadata *sys_data; > @@ -178,6 +135,8 @@ void ftrace_syscall_exit(struct pt_regs *regs) > int syscall_nr; > > syscall_nr = syscall_get_nr(current, regs); > + if (!test_bit(syscall_nr, enabled_exit_syscalls)) > + return; 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> --- kernel/trace/trace_syscalls.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/kernel/trace/trace_syscalls.c +++ b/kernel/trace/trace_syscalls.c @@ -224,6 +224,8 @@ void ftrace_syscall_enter(struct pt_regs int syscall_nr; syscall_nr = syscall_get_nr(current, regs); + if (syscall_nr < 0) + return; if (!test_bit(syscall_nr, enabled_enter_syscalls)) return; @@ -254,6 +256,8 @@ void ftrace_syscall_exit(struct pt_regs int syscall_nr; syscall_nr = syscall_get_nr(current, regs); + if (syscall_nr < 0) + return; if (!test_bit(syscall_nr, enabled_exit_syscalls)) return;
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