Re: [PATCH 3/6] x86: clean up _TIF_SYSCALL_EMU handling using ptrace_syscall_enter hook

[Haibo Xu (Arm Technology China)]

On 2019/3/1 2:32, Sudeep Holla wrote:
> Now that we have a new hook ptrace_syscall_enter that can be called from
> syscall entry code and it handles PTRACE_SYSEMU in generic code, we
> can do some cleanup using the same in syscall_trace_enter.
>
> Further the extra logic to find single stepping PTRACE_SYSEMU_SINGLESTEP
> in syscall_slow_exit_work seems unnecessary. Let's remove the same.

I think we should not change the logic here. Is so, it will double the report of syscall
when PTRACE_SYSEMU_SINGLESTEP is enabled.

>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> ---
>  arch/x86/entry/common.c | 22 ++++------------------
>  1 file changed, 4 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
> index 7bc105f47d21..36457c1f87d2 100644
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -70,22 +70,16 @@ static long syscall_trace_enter(struct pt_regs *regs)
>
>  struct thread_info *ti = current_thread_info();
>  unsigned long ret = 0;
> -bool emulated = false;
>  u32 work;
>
>  if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
>  BUG_ON(regs != task_pt_regs(current));
>
> -work = READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
> -
> -if (unlikely(work & _TIF_SYSCALL_EMU))
> -emulated = true;
> -
> -if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
> -    tracehook_report_syscall_entry(regs))
> +if (unlikely(ptrace_syscall_enter(regs)))
>  return -1L;
>
> -if (emulated)
> +work = READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
> +if ((work & _TIF_SYSCALL_TRACE) && tracehook_report_syscall_entry(regs))
>  return -1L;
>
>  #ifdef CONFIG_SECCOMP
> @@ -227,15 +221,7 @@ static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
>  if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
>  trace_sys_exit(regs, regs->ax);
>
> -/*
> - * If TIF_SYSCALL_EMU is set, we only get here because of
> - * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
> - * We already reported this syscall instruction in
> - * syscall_trace_enter().
> - */
> -step = unlikely(
> -(cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
> -== _TIF_SINGLESTEP);
> +step = unlikely((cached_flags & _TIF_SINGLESTEP));
>  if (step || cached_flags & _TIF_SYSCALL_TRACE)
>  tracehook_report_syscall_exit(regs, step);
>  }
>
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