linux-kernel - Re: [PATCH] arm64: make a single hook to syscall

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Date:	Wed, 19 Feb 2014 20:53:16 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Will Deacon <will.deacon@....com>
CC:	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"eparis@...hat.com" <eparis@...hat.com>,
	"rgb@...hat.com" <rgb@...hat.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"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>,
	"linux-audit@...hat.com" <linux-audit@...hat.com>,
	"patches@...aro.org" <patches@...aro.org>
Subject: Re: [PATCH] arm64: make a single hook to syscall_trace() for all
 syscall features

Hi,

On 02/18/2014 02:35 AM, Will Deacon wrote:
> On Fri, Feb 07, 2014 at 10:07:31AM +0000, AKASHI Takahiro wrote:
>> Currently syscall_trace() is called only for ptrace.
>> With additional TIF_xx flags introduced, it is now called in all the cases
>> of audit, ftrace and seccomp in addition to ptrace.
>> Those features will be implemented later, but it's safe to include them
>> now because they can not be turned on anyway.
>>
>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
>> ---
>>   arch/arm64/include/asm/thread_info.h |   13 +++++++++++++
>>   arch/arm64/kernel/entry.S            |    5 +++--
>>   arch/arm64/kernel/ptrace.c           |   11 +++++------
>>   3 files changed, 21 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
>> index 720e70b..c3df797 100644
>> --- a/arch/arm64/include/asm/thread_info.h
>> +++ b/arch/arm64/include/asm/thread_info.h
>
> [...]
>
>> +#define _TIF_WORK_SYSCALL	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
>> +				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP)
>
> This is called _TIF_SYSCALL_WORK on arch/arm/, any reason not to follow the
> naming convention here?

This is called _TIF_WORK_SYSCALL on arch/x86 :-)
That is the only reason, and so I don't have any objection to following arm
if you prefer it.

>>   #endif /* __KERNEL__ */
>>   #endif /* __ASM_THREAD_INFO_H */
>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>> index 39ac630..c94b2ab 100644
>> --- a/arch/arm64/kernel/entry.S
>> +++ b/arch/arm64/kernel/entry.S
>> @@ -631,8 +631,9 @@ el0_svc_naked:					// compat entry point
>>   	enable_irq
>>
>>   	get_thread_info tsk
>> -	ldr	x16, [tsk, #TI_FLAGS]		// check for syscall tracing
>> -	tbnz	x16, #TIF_SYSCALL_TRACE, __sys_trace // are we tracing syscalls?
>> +	ldr	x16, [tsk, #TI_FLAGS]		// check for syscall hooks
>> +	tst	x16, #_TIF_WORK_SYSCALL
>> +	b.ne	__sys_trace
>>   	adr	lr, ret_fast_syscall		// return address
>>   	cmp     scno, sc_nr                     // check upper syscall limit
>>   	b.hs	ni_sys
>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index 6a8928b..64ce39f 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -1062,9 +1062,6 @@ asmlinkage int syscall_trace(int dir, struct pt_regs *regs)
>>   {
>>   	unsigned long saved_reg;
>>
>> -	if (!test_thread_flag(TIF_SYSCALL_TRACE))
>> -		return regs->syscallno;
>
> This doesn't look right for things like audit (where we don't want to report
> the syscall if only _TIF_SYSCALL_AUDIT is set, for example).

Yeah, it is my screwup.
I will add the guards against TIF_SYSCALL_TRACE (for ptrace),
TIF_SYSCALL_TRACEPOINT (for ftrace) and TIF_SYSCALL_AUDIT (for audit).

secure_computing() is protected in itself.

>>   	if (is_compat_task()) {
>>   		/* AArch32 uses ip (r12) for scratch */
>>   		saved_reg = regs->regs[12];
>> @@ -1078,10 +1075,12 @@ asmlinkage int syscall_trace(int dir, struct pt_regs *regs)
>>   		regs->regs[7] = dir;
>>   	}
>>
>> -	if (dir)
>> +	if (dir) {
>>   		tracehook_report_syscall_exit(regs, 0);
>> -	else if (tracehook_report_syscall_entry(regs))
>> -		regs->syscallno = ~0UL;
>> +	} else {
>> +		if (tracehook_report_syscall_entry(regs))
>> +			regs->syscallno = ~0UL;
>> +	}
>
> This hunk doesn't do anything.

Well, this is just a change for future patches, but
I will remove it anyway due to the guards mentioned above.

-Takahiro AKASHI

> Will
>
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