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  • Hendrik Brueckner's avatar
    tracing: Check invalid syscall nr while tracing syscalls · cd0980fc
    Hendrik Brueckner authored
    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 include 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: default avatarHendrik Brueckner <>
    Acked-by: default avatarHeiko Carstens <>
    Cc: Jason Baron <>
    Cc: Frederic Weisbecker <>
    Cc: Ingo Molnar <>
    Cc: Lai Jiangshan <>
    Cc: Steven Rostedt <>
    Cc: Peter Zijlstra <>
    Cc: Mathieu Desnoyers <>
    Cc: Jiaying Zhang <>
    Cc: Martin Bligh <>
    Cc: Li Zefan <>
    Cc: Martin Schwidefsky <>
    Cc: Paul Mundt <>
    LKML-Reference: <>
    Signed-off-by: default avatarFrederic Weisbecker <>