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

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Date:	Thu, 27 Nov 2014 14:53:36 +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 11/26/2014 09:41 PM, Will Deacon wrote:
> Hi Akashi,
>
> 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?


Thanks,
-Takahiro AKASHI

> Will
>
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