Messages in this thread | | | Date | Mon, 1 Sep 2014 12:37:55 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v6 2/6] arm64: ptrace: allow tracer to skip a system call |
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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.
> 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.
Will
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