linux-kernel - Re: [PATCH v2 2/3] arm64: Add seccomp support

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Date:	Thu, 06 Mar 2014 11:34:46 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Will Deacon <will.deacon@....com>
CC:	"wad@...omium.org" <wad@...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 v2 2/3] arm64: Add seccomp support

On 03/01/2014 02:20 AM, Will Deacon wrote:
> On Tue, Feb 25, 2014 at 09:20:24AM +0000, AKASHI Takahiro wrote:
>> secure_computing() should always be called first in syscall_trace(), and
>> if it returns non-zero, we should stop further handling. Then that system
>> call may eventually fail, be trapped or the process itself be killed
>> depending on loaded rules.
>
> [...]
>
>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index d4ce70e..f2a74bc 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -20,12 +20,14 @@
>>    */
>>
>>   #include <linux/audit.h>
>> +#include <linux/errno.h>
>>   #include <linux/kernel.h>
>>   #include <linux/sched.h>
>>   #include <linux/mm.h>
>>   #include <linux/smp.h>
>>   #include <linux/ptrace.h>
>>   #include <linux/user.h>
>> +#include <linux/seccomp.h>
>>   #include <linux/security.h>
>>   #include <linux/init.h>
>>   #include <linux/signal.h>
>> @@ -1064,6 +1066,10 @@ asmlinkage int syscall_trace(int dir, struct pt_regs *regs)
>>   {
>>   	unsigned long saved_reg;
>>
>> +	if (!dir && secure_computing((int)regs->syscallno))
>
> Why do you need this cast to (int)?

OK. I will remove it because gcc doesn't complain about it anyway.

> Also, it's probably better to check for
> -1 explicitly here.

I wil fix it.

> I'm slightly surprised that we do the secure computing check first. Doesn't
> this allow a debugger to change the syscall to something else after we've
> decided that it's ok?

To be honest, I just followed other architectures' implementation.
Can you elaborate any use case that you have in your mind?

-Takahiro AKASHI

> Will
>
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