Re: [PATCH] arm: ptrace: fix syscall modification under PTRACE_O_TRACESECCOMP

[AKASHI Takahiro]

Hi Will,

On 06/24/2014 05:54 PM, Will Deacon wrote:
> On Mon, Jun 23, 2014 at 08:46:52PM +0100, Kees Cook wrote:
> > On Mon, Jun 23, 2014 at 1:46 AM, Will Deacon <will.deacon@xxxxxxx> wrote:
> > > On Fri, Jun 20, 2014 at 07:10:46PM +0100, Kees Cook wrote:
> > > > On Fri, Jun 20, 2014 at 10:36 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > > > > On Fri, Jun 20, 2014 at 10:23 AM, Will Deacon <will.deacon@xxxxxxx> wrote:
> > > > > > Right, gotcha. Thanks for the explanation. I was confused, because
> > > > > > tracehook_report_syscall does the right thing (returns
> > > > > > current_thread_info()->syscall), but if we don't have TIF_SYSCALL_TRACE set,
> > > > > > then updates during the secure_computing callback will be ignored.re
> > > > > >
> > > > > > However, my fix to this is significantly smaller than your patch, so I fear
> > > > > > I'm still missing something.
> > > > >
> > > > > Oh, yes, that's much smaller. Nice! I will test this and report back.
> > > >
> > > > Yup, I can confirm this works. Thanks!
> > > >
> > > > Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > >
> > > Thanks, Kees. I'll post a patch shortly. I'll try and remember to keep an
> > > eye out for this when seccomp lands for arm64 too.
> >
> > Great, thanks!
> >
> > What's the state of seccomp on arm64? I saw a series back in March,
> > but nothing since then? It looked complete, but I haven't set up a
> > test environment yet to verify.
>
> I think Akashi was going to repost `real soon now' so we can include them
> for 3.17. He missed the merge window last time around.

I took a quick look at the current implementation of ptrace.
ptrace(PTRACE_GETREGSET/SETREGSET), eventually gpr_get/set(), handles only 'struct user_pt_regs',
and we have no way to modify orig_x0 nor syscallno in 'struct pt_regs' directly.
So it seems to me that we can't change a system call by ptrace().
Do I misunderstand anything?

-Takahiro AKASHI


> Will
>
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