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

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Date:	Fri, 08 Aug 2014 16:35:42 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Kees Cook <keescook@...omium.org>
CC:	Andy Lutomirski <luto@...capital.net>,
	Deepak Saxena <dsaxena@...aro.org>,
	Will Drewry <wad@...omium.org>, linaro-kernel@...ts.linaro.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Lee Campbell <leecam@...gle.com>
Subject: Re: [PATCH v5 3/3] arm64: Add seccomp support

On 08/06/2014 12:08 AM, Kees Cook wrote:
> On Fri, Jul 25, 2014 at 2:37 AM, AKASHI Takahiro
> <takahiro.akashi@...aro.org> 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.

>> I'm sure that my next version should work with 32/64-bit tracers on 64-bit
>> kernel.
>
> Do you have a git tree uploaded anywhere? I'd love to follow this more
> closely. When do you expect a v6?

I'd like to submit v6 as soon as possible, but
(1) how we should handle syscall(-1) is annoying me.
     Without ptracer, we will normally return -ENOSYS but, for example,
     what if some seccomp filter is installed and it does allow (or doesn't
     have any rule against) '-1' syscall? Since the kernel doesn't know tracer's
     intention, we should just let syscall(-1) return a bogus value.
     Thus we will see inconsistent results of syscall(-1).

(2) I'm investigating some failures in Kees' test suite.
   * 'TRACE.handler' case on compat task:
     Now I found a bug in arm64's compat_siginfo_t and fixed it.
   * 'TSYNC.two_siblings_*' cases on 32/64-bit task:
     I rebased my patch on pre-v3.17-rc1, but those cases still fail.
     I have no clues at this moment.

So please be patient for a while.

-Takahiro AKASHI


> Thanks!
>
> -Kees
>
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