Re: [PATCH v7 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL

[Will Deacon <will.deacon@arm.com>]

On Wed, Oct 08, 2014 at 04:30:18PM +0100, Kees Cook wrote:
> On Wed, Oct 8, 2014 at 9:13 AM, Will Deacon <will.deacon@arm.com> wrote:
> > On Thu, Oct 02, 2014 at 10:46:11AM +0100, AKASHI Takahiro wrote:
> >> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> >> index fe63ac5..2842f9f 100644
> >> --- a/arch/arm64/kernel/ptrace.c
> >> +++ b/arch/arm64/kernel/ptrace.c
> >> @@ -1082,7 +1082,19 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task)
> >>  long arch_ptrace(struct task_struct *child, long request,
> >>                unsigned long addr, unsigned long data)
> >>  {
> >> -     return ptrace_request(child, request, addr, data);
> >> +     int ret;
> >> +
> >> +     switch (request) {
> >> +             case PTRACE_SET_SYSCALL:
> >> +                     task_pt_regs(child)->syscallno = data;
> >> +                     ret = 0;
> >> +                     break;
> >> +             default:
> >> +                     ret = ptrace_request(child, request, addr, data);
> >> +                     break;
> >> +     }
> >> +
> >> +     return ret;
> >>  }
> >
> > I still don't understand why this needs to be in arch-specific code. Can't
> > we implement this in generic code and get architectures to implement
> > something like syscall_set_nr if they want the generic interface?
> 
> Personally, I'd rather see this land as-is in the arm64 tree, and then
> later optimize PTRACE_SET_SYSCALL out of arm/ and arm64/, especially
> since only these architectures implement this at the moment.

Why? It should be really straightforward to do this in core code from the
get-go and experience shows that, if we don't do it now, it will never
happen.

> This is my plan for the asm-generic seccomp.h too -- I'd rather avoid
> touching other architectures in this series, as it's easier to review
> this way. Then we can optimize the code in a separate series, which
> will have those changes isolated, etc.

But this doesn't need to touch any other architectures...

Will