On Thu, 29 Jun 2017 11:38:11 +0200
Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> Zorro reported following crash while having enabled
> syscall tracing (CONFIG_FTRACE_SYSCALLS):
>
> Unable to handle kernel pointer dereference at virtual ...
> Oops: 0011 [#1] SMP DEBUG_PAGEALLOC
>
> SNIP
>
> Call Trace:
> ([<000000000024d79c>] ftrace_syscall_enter+0xec/0x1d8)
> [<00000000001099c6>] do_syscall_trace_enter+0x236/0x2f8
> [<0000000000730f1c>] sysc_tracesys+0x1a/0x32
> [<000003fffcf946a2>] 0x3fffcf946a2
> INFO: lockdep is turned off.
> Last Breaking-Event-Address:
> [<000000000022dd44>] rb_event_data+0x34/0x40
> ---[ end trace 8c795f86b1b3f7b9 ]---
>
> The crash happens in syscall_get_arguments function for
> syscalls with zero arguments, that will try to access
> first argument (args[0]) in event entry, but it's not
> allocated.
>
> Bail out of there are no arguments.
>
> Reported-by: Zorro Lang <zlang@xxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> arch/s390/include/asm/syscall.h | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
There are callers of syscall_get_arguments with n=0. And it makes
sense to check for this case in the function instead of forcing all
callers to check for it.
> diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h
> index 6ba0bf928909..5f7c11c932fa 100644
> --- a/arch/s390/include/asm/syscall.h
> +++ b/arch/s390/include/asm/syscall.h
> @@ -64,14 +64,22 @@ static inline void syscall_get_arguments(struct task_struct *task,
> {
> unsigned long mask = -1UL;
>
> + /*
> + * No arguments for this syscall, there's nothing to do.
> + */
> + if (!n)
> + return;
> +
> BUG_ON(i + n > 6);
So yes, for this part of the patch.
> #ifdef CONFIG_COMPAT
> if (test_tsk_thread_flag(task, TIF_31BIT))
> mask = 0xffffffff;
> #endif
> - while (n-- > 0)
> + while (n-- > 0) {
> if (i + n > 0)
> args[n] = regs->gprs[2 + i + n] & mask;
> + }
> +
> if (i == 0)
> args[0] = regs->orig_gpr2 & mask;
> }
But why the unrelated whitespace damage with the additional { } ?
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
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