Subject: Re: [PATCH v2 4/6] powerpc: use common ptrace_syscall_enter hook to handle _TIF_SYSCALL_EMU

From: Sudeep Holla <[email-masked]>
Date: Mon, 18 Mar 2019 14:59:11 +0000

On Mon, Mar 18, 2019 at 05:26:18PM +0300, Dmitry V. Levin wrote:
> On Mon, Mar 18, 2019 at 10:49:23AM +0000, 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 do_syscall_trace_enter.
> > 
> > Cc: Oleg Nesterov <[email-masked]>
> > Cc: Paul Mackerras <[email-masked]>
> > Cc: Michael Ellerman <[email-masked]>
> > Signed-off-by: Sudeep Holla <[email-masked]>
> > ---
> >  arch/powerpc/kernel/ptrace.c | 48 ++++++++++++++++--------------------
> >  1 file changed, 21 insertions(+), 27 deletions(-)
> > 
> > diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> > index 2e2183b800a8..05579a5dcb12 100644
> > --- a/arch/powerpc/kernel/ptrace.c
> > +++ b/arch/powerpc/kernel/ptrace.c
> > @@ -3278,35 +3278,29 @@ long do_syscall_trace_enter(struct pt_regs *regs)
> >  
> >  	user_exit();
> >  
> > -	flags = READ_ONCE(current_thread_info()->flags) &
> > -		(_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
> > -
> > -	if (flags) {
> > -		int rc = tracehook_report_syscall_entry(regs);
> > +	if (unlikely(ptrace_syscall_enter(regs))) {
> > +		/*
> > +		 * A nonzero return code from tracehook_report_syscall_entry()
> > +		 * tells us to prevent the syscall execution, but we are not
> > +		 * going to execute it anyway.
> > +		 *
> > +		 * Returning -1 will skip the syscall execution. We want to
> > +		 * avoid clobbering any registers, so we don't goto the skip
> > +		 * label below.
> > +		 */
> > +		return -1;
> > +	}
> 
> This comment is out of sync with the changed code.

Still applicable indirectly as ptrace_syscall_enter just executes
tracehook_report_syscall_entry, but I agree needs rewording, will update.

--
Regards,
Sudeep