Re: [RFC] ptrace: add generic SET_SYSCALL request

[AKASHI Takahiro]

Will,

On 11/07/2014 11:04 PM, Oleg Nesterov wrote:
> On 11/07, AKASHI Takahiro wrote:
> > --- a/arch/arm/kernel/ptrace.c
> > +++ b/arch/arm/kernel/ptrace.c
> > @@ -853,11 +853,6 @@ long arch_ptrace(struct task_struct *child, long request,
> >   				       datap);
> >   			break;
> >
> > -		case PTRACE_SET_SYSCALL:
> > -			task_thread_info(child)->syscall = data;
> > -			ret = 0;
> > -			break;
> > -
> >   #ifdef CONFIG_CRUNCH
> >   		case PTRACE_GETCRUNCHREGS:
> >   			ret = ptrace_getcrunchregs(child, datap);
> > diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> > index 54e7522..d7048fa 100644
> > --- a/kernel/ptrace.c
> > +++ b/kernel/ptrace.c
> > @@ -1001,6 +1001,12 @@ int ptrace_request(struct task_struct *child, long request,
> >   		break;
> >   	}
> >   #endif
> > +
> > +#ifdef PTRACE_SET_SYSCALL
> > +	case PTRACE_SET_SYSCALL:
> > +		ret = syscall_set_nr(child, task_pt_regs(child), data);
> > +		break;
> > +#endif
>
> I too do not understand why it makes sense to move PTRACE_SET_SYSCALL into
> the common kernel/ptrace.c.

I think I explained why we need a new (atomic) interface of changing a system
call number while tracing with ptrace. But I don't have a strong preference,
either ptrace(SET_SYSCALL) or ptrace(SETREGSET, NT_SYSTEM_CALL).

> To me the fact that PTRACE_SET_SYSCALL can be undefined and syscall_set_nr()
> is very much arch-dependant (but most probably trivial) means that this  code
> should live in arch_ptrace().

Thinking of Oleg's comment above, it doesn't make sense neither to define generic
NT_SYSTEM_CALL (user_regset) in uapi/linux/elf.h and implement it in ptrace_regset()
in kernel/ptrace.c with arch-defined syscall_(g)set_nr().

Since we should have the same interface on arm and arm64, we'd better implement
ptrace(PTRACE_SET_SYSCALL) locally on arm64 for now (as I originally submitted).

-Takahiro AKASHI

> In any case, I think it doesn't make sense to pass task_pt_regs(child), this
> helper can do this itself if it needs struct pt_regs.
>
> Oleg.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/