Re: [PATCH v6 2/6] arm64: ptrace: allow tracer to skip a system call

[AKASHI Takahiro]

On 09/01/2014 08:37 PM, Will Deacon wrote:
> On Wed, Aug 27, 2014 at 06:55:46AM +0100, AKASHI Takahiro wrote:
> > On 08/27/2014 02:51 AM, Will Deacon wrote:
> > > On Fri, Aug 22, 2014 at 01:35:17AM +0100, AKASHI Takahiro wrote:
> > > > Oops, you're absolutely right. I didn't think of this case.
> > > > syscall_trace_enter() should not return a syscallno directly, but always
> > > > return -1 if syscallno < 0. (except when secure_computing() returns with -1)
> > > > This also implies that tracehook_report_syscall() should also have a return value.
> > > >
> > > > Will, is this fine with you?
> > >
> > > Well, the first thing that jumps out at me is why this is being done
> > > completely differently for arm64 and arm. I thought adding the new ptrace
> > > requests would reconcile the differences?
> >
> > I'm not sure what portion of my code you mentioned as "completely different", but
> >
> > 1)
> > setting x0 to -ENOSYS is necessary because, otherwise, user-issued syscall(-1) will
> > return a bogus value when audit tracing is on.
> >
> > Please note that, on arm,
> >                    not traced      traced
> >                    ------          ------
> > syscall(-1)      aborted         OOPs(BUG_ON)
> > syscall(-3000)   aborted         aborted
> > syscall(1000)    ENOSYS          ENOSYS
> >
> > So, anyhow, its a bit difficult and meaningless to mimic these invalid cases.
>
> I'm not suggesting we make ourselves bug-compatible with ARM. Instead, I'd
> rather see a series of patches getting the ARM code working correctly,
> before we go off doing something different for arm64.

I see.

> > 2)
> > branching a new label, syscall_trace_return_skip (see entry.S), after syscall_trace_enter()
> > is necessary in order to avoid OOPS in audit_syscall_enter() as we discussed.
> >
> > Did I make it clear?
>
> Sure. So let's fix ARM, then look at the arm64 port after that. I really
> want to avoid divergence in this area.

Okey, I will start with fixing the issue on arm.

-Takahiro AKASHI

> Will
--
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/