Re: [PATCH v2 2/6] ptrace: introduce ptrace_syscall_enter to consolidate PTRACE_SYSEMU handling

[Sudeep Holla <sudeep.holla@arm.com>]

On Mon, Mar 18, 2019 at 05:31:47PM +0300, Dmitry V. Levin wrote:
> On Mon, Mar 18, 2019 at 10:49:21AM +0000, Sudeep Holla wrote:
> > Currently each architecture handles PTRACE_SYSEMU in very similar way.
> > It's completely arch independent and can be handled in the code helping
> > to consolidate PTRACE_SYSEMU handling.
> > 
> > Let's introduce a hook 'ptrace_syscall_enter' that arch specific syscall
> > entry code can call.
> > 
> > Cc: Oleg Nesterov <oleg@redhat.com>
> > Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> > ---
> >  include/linux/ptrace.h |  1 +
> >  kernel/ptrace.c        | 22 ++++++++++++++++++++++
> >  2 files changed, 23 insertions(+)
> > 
> > diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
> > index edb9b040c94c..e30f51e3363e 100644
> > --- a/include/linux/ptrace.h
> > +++ b/include/linux/ptrace.h
> > @@ -407,6 +407,7 @@ static inline void user_single_step_report(struct pt_regs *regs)
> >  #define current_user_stack_pointer() user_stack_pointer(current_pt_regs())
> >  #endif
> >  
> > +extern long ptrace_syscall_enter(struct pt_regs *regs);
> >  extern int task_current_syscall(struct task_struct *target, long *callno,
> >  				unsigned long args[6], unsigned int maxargs,
> >  				unsigned long *sp, unsigned long *pc);
> > diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> > index 4fa3b7f4c3c7..c9c505c483df 100644
> > --- a/kernel/ptrace.c
> > +++ b/kernel/ptrace.c
> > @@ -29,6 +29,7 @@
> >  #include <linux/hw_breakpoint.h>
> >  #include <linux/cn_proc.h>
> >  #include <linux/compat.h>
> > +#include <linux/tracehook.h>
> >  
> >  /*
> >   * Access another process' address space via ptrace.
> > @@ -557,6 +558,27 @@ static int ptrace_detach(struct task_struct *child, unsigned int data)
> >  	return 0;
> >  }
> >  
> > +/*
> > + * Hook to check and report for PTRACE_SYSEMU, can be called from arch
> > + * arch syscall entry code
> > + */
> > +long ptrace_syscall_enter(struct pt_regs *regs)
> > +{
> > +#ifdef TIF_SYSCALL_EMU
> > +	if (test_thread_flag(TIF_SYSCALL_EMU)) {
> > +		if (tracehook_report_syscall_entry(regs))
> > +			/*
> > +			 * We can ignore the return code here as we need
> > +			 * return -1 always for syscall emulation irrespective
> > +			 * of whether the tracehook report fails or succeed.
> > +			 */
> > +			;
> 
> This is problematic as it causes build errors with -Werror=empty-body,
> see https://lore.kernel.org/lkml/20181218205305.26647-1-malat@debian.org/
> 

Thanks for the pointer, will update.

--
Regards,
Sudeep