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

Open Source and information security mailing list archives

Message-ID: <53B5098B.9050801@linaro.org>
Date:	Thu, 03 Jul 2014 16:43:07 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Will Deacon <will.deacon@....com>,
	Kees Cook <keescook@...omium.org>
CC:	André Hentschel <nerv@...ncrow.de>,
	Russell King <linux@....linux.org.uk>,
	Jonathan Austin <Jonathan.Austin@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Ricky Zhou <rickyz@...gle.com>
Subject: Re: [PATCH] arm: ptrace: fix syscall modification under PTRACE_O_TRACESECCOMP

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@....com> 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@...omium.org> wrote:
>>>>> On Fri, Jun 20, 2014 at 10:23 AM, Will Deacon <will.deacon@....com> 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@...omium.org>
>>>
>>> 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
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> 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@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives