linux-kernel - Re: [PATCH v7 1/6] arm64: ptrace: add PTRACE_SET

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Date:	Thu, 06 Nov 2014 11:40:15 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Will Deacon <will.deacon@....com>,
	Kees Cook <keescook@...omium.org>
CC:	Catalin Marinas <Catalin.Marinas@....com>,
	"dsaxena@...aro.org" <dsaxena@...aro.org>,
	"arndb@...db.de" <arndb@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL

Hi Will, Kees

#Sorry for this late ping,

On 10/09/2014 06:23 PM, Will Deacon wrote:
> On Wed, Oct 08, 2014 at 04:30:18PM +0100, Kees Cook wrote:
>> On Wed, Oct 8, 2014 at 9:13 AM, Will Deacon <will.deacon@....com> wrote:
>>> On Thu, Oct 02, 2014 at 10:46:11AM +0100, AKASHI Takahiro wrote:
>>>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>>>> index fe63ac5..2842f9f 100644
>>>> --- a/arch/arm64/kernel/ptrace.c
>>>> +++ b/arch/arm64/kernel/ptrace.c
>>>> @@ -1082,7 +1082,19 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task)
>>>>   long arch_ptrace(struct task_struct *child, long request,
>>>>                 unsigned long addr, unsigned long data)
>>>>   {
>>>> -     return ptrace_request(child, request, addr, data);
>>>> +     int ret;
>>>> +
>>>> +     switch (request) {
>>>> +             case PTRACE_SET_SYSCALL:
>>>> +                     task_pt_regs(child)->syscallno = data;
>>>> +                     ret = 0;
>>>> +                     break;
>>>> +             default:
>>>> +                     ret = ptrace_request(child, request, addr, data);
>>>> +                     break;
>>>> +     }
>>>> +
>>>> +     return ret;
>>>>   }
>>>
>>> I still don't understand why this needs to be in arch-specific code. Can't
>>> we implement this in generic code and get architectures to implement
>>> something like syscall_set_nr if they want the generic interface?
>>
>> Personally, I'd rather see this land as-is in the arm64 tree, and then
>> later optimize PTRACE_SET_SYSCALL out of arm/ and arm64/, especially
>> since only these architectures implement this at the moment.
>
> Why? It should be really straightforward to do this in core code from the
> get-go and experience shows that, if we don't do it now, it will never
> happen.

How should I deal with this issue? I would be able to go either way.

Other than that, I will submit v8 patch series with a few very minor updates:
- use compat_uint_t in struct compat_siginfo
- use a new call interface of secure_computing(void)
- modify and clarify comments in syscall_trace_enter()

Thanks,
-Takahiro AKASHI

>> This is my plan for the asm-generic seccomp.h too -- I'd rather avoid
>> touching other architectures in this series, as it's easier to review
>> this way. Then we can optimize the code in a separate series, which
>> will have those changes isolated, etc.
>
> But this doesn't need to touch any other architectures...
>
> Will
>
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