linux-kernel - Re: [PATCH v9 1/6] arm64: ptrace: add NT_ARM_SYSTEM

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Message-ID: <5478075E.4000203@linaro.org>
Date:	Fri, 28 Nov 2014 14:25:50 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Will Deacon <will.deacon@....com>
CC:	"keescook@...omium.org" <keescook@...omium.org>,
	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 v9 1/6] arm64: ptrace: add NT_ARM_SYSTEM_CALL regset

On 11/27/2014 11:10 PM, Will Deacon wrote:
> On Thu, Nov 27, 2014 at 05:53:36AM +0000, AKASHI Takahiro wrote:
>> On 11/26/2014 09:41 PM, Will Deacon wrote:
>>> On Wed, Nov 26, 2014 at 04:49:46AM +0000, AKASHI Takahiro wrote:
>>>> This regeset is intended to be used to get and set a system call number
>>>> while tracing.
>>>> There was some discussion about possible approaches to do so:
>>>>
>>>> (1) modify x8 register with ptrace(PTRACE_SETREGSET) indirectly,
>>>>       and update regs->syscallno later on in syscall_trace_enter(), or
>>>> (2) define a dedicated regset for this purpose as on s390, or
>>>> (3) support ptrace(PTRACE_SET_SYSCALL) as on arch/arm
>>>>
>>>> Thinking of the fact that user_pt_regs doesn't expose 'syscallno' to
>>>> tracer as well as that secure_computing() expects a changed syscall number,
>>>> especially case of -1, to be visible before this function returns in
>>>> syscall_trace_enter(), (1) doesn't work well.
>>>> We will take (2) since it looks much cleaner.
>>>>
>>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
>>>> ---
>>>>    arch/arm64/kernel/ptrace.c |   35 +++++++++++++++++++++++++++++++++++
>>>>    include/uapi/linux/elf.h   |    1 +
>>>>    2 files changed, 36 insertions(+)
>>>>
>>>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>>>> index 8a4ae8e..8b98781 100644
>>>> --- a/arch/arm64/kernel/ptrace.c
>>>> +++ b/arch/arm64/kernel/ptrace.c
>>>> @@ -551,6 +551,32 @@ static int tls_set(struct task_struct *target, const struct user_regset *regset,
>>>>    	return ret;
>>>>    }
>>>>
>>>> +static int system_call_get(struct task_struct *target,
>>>> +			   const struct user_regset *regset,
>>>> +			   unsigned int pos, unsigned int count,
>>>> +			   void *kbuf, void __user *ubuf)
>>>> +{
>>>> +	struct pt_regs *regs = task_pt_regs(target);
>>>> +
>>>> +	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
>>>> +				   &regs->syscallno, 0, -1);
>>>
>>> Does this work for big-endian machines? regs->syscallno is a u64, but the
>>> regset defines it as an int. I think you need to copy to a temporary
>>> register first.
>>
>> Right. I will fix it.
>> Do you prefer to use s32, instead of int, like other regsets?
>
> I don't have a preference either way.
>
> It would be great to have a new revision of these patches ASAP if you're
> targetting 3.19.

Yeah, definitely.

-Takahiro AKASHI

> Will
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