Re: [PATCH v5 3/3] arm64: Add seccomp support

[AKASHI Takahiro]

Will,

On 08/11/2014 06:24 PM, Will Deacon wrote:
> On Fri, Aug 08, 2014 at 08:35:42AM +0100, AKASHI Takahiro wrote:
> > On 08/06/2014 12:08 AM, Kees Cook wrote:
> > > On Fri, Jul 25, 2014 at 2:37 AM, AKASHI Takahiro
> > > <takahiro.akashi@xxxxxxxxxx> wrote:
> > > > I found a bug in my current patch (v5). When 32-bit tracer skips a system call,
> > > > we should not update syscallno from x8 since syscallno is re-written directly
> > > > via ptrace(PTRACE_SET_SYSCALL).
> > >
> > > Ah, yes. Will aarch64 have a PTRACE_SET_SYSCALL option, or is this
> > > strictly a 32-bit vs 64-bit issue?
> >
> > As discussed in a few weeks ago, aarch64 won't support PTRACE_SET_SYSCALL.
>
> Well, I don't think anything was set in stone. If you have a compelling
> reason why adding the new request gives you something over setting w8
> directly, then we can extend ptrace.

Yeah, I think I may have to change my mind. Looking into __secure_computing(),
I found the code below:

>     case SECCOMP_MODE_FILTER:
>         case SECCOMP_RET_TRACE:
>             ...
>             if (syscall_get_nr(current, regs) < 0)
>                 goto skip;

This implies that we should modify syscallno *before* __secure_computing() returns.

I assumed, in my next version, we could skip a system call by overwriting syscallno
with x8 in syscall_trace_enter() after __secure_computing() returns 0, and it actually
works.
But we'd better implement PTRACE_SET_SYSCALL to comply with what __secure_computing()
expects.

-Takahiro AKASHI


> Will
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
--
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/