Subject: [PATCH v2 1/1] arm64: make a single hook to syscall_trace() for all syscall features

From: [email-masked] (AKASHI Takahiro)
Date: Thu, 27 Feb 2014 10:33:38 +0900

On 02/26/2014 08:25 PM, Will Deacon wrote:
> On Wed, Feb 26, 2014 at 02:00:19AM +0000, AKASHI Takahiro wrote:
>> On 02/26/2014 12:00 AM, Will Deacon wrote:
>>> On Tue, Feb 25, 2014 at 09:14:43AM +0000, AKASHI Takahiro wrote:
>>>> Currently syscall_trace() is called only for ptrace.
>>>> With additional TIF_xx flags defined, it is now called in all the cases
>>>> of audit, ftrace and seccomp in addition to ptrace.
>>>>
>>>> Signed-off-by: AKASHI Takahiro <[email-masked]>
>>>> Acked-by: Richard Guy Briggs <[email-masked]>
>>>> ---
>>>>    arch/arm64/include/asm/thread_info.h |   13 ++++++++++
>>>>    arch/arm64/kernel/entry.S            |    5 ++--
>>>>    arch/arm64/kernel/ptrace.c           |   45 +++++++++++++++++-----------------
>>>>    3 files changed, 38 insertions(+), 25 deletions(-)
>>
>> [...]
>>
>>>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>>>> index 6a8928b..c70133e 100644
>>>> --- a/arch/arm64/kernel/ptrace.c
>>>> +++ b/arch/arm64/kernel/ptrace.c
>>>> @@ -1062,31 +1062,30 @@ asmlinkage int syscall_trace(int dir, struct pt_regs *regs)
>>>>    {
>>>>    	unsigned long saved_reg;
>>>>
>>>> -	if (!test_thread_flag(TIF_SYSCALL_TRACE))
>>>> -		return regs->syscallno;
>>>> -
>>>> -	if (is_compat_task()) {
>>>> -		/* AArch32 uses ip (r12) for scratch */
>>>> -		saved_reg = regs->regs[12];
>>>> -		regs->regs[12] = dir;
>>>> -	} else {
>>>> -		/*
>>>> -		 * Save X7. X7 is used to denote syscall entry/exit:
>>>> -		 *   X7 = 0 -> entry, = 1 -> exit
>>>> -		 */
>>>> -		saved_reg = regs->regs[7];
>>>> -		regs->regs[7] = dir;
>>>> -	}
>>>> +	if (test_thread_flag(TIF_SYSCALL_TRACE)) {
>>>> +		if (is_compat_task()) {
>>>> +			/* AArch32 uses ip (r12) for scratch */
>>>> +			saved_reg = regs->regs[12];
>>>> +			regs->regs[12] = dir;
>>>> +		} else {
>>>> +			/*
>>>> +			 * Save X7. X7 is used to denote syscall entry/exit:
>>>> +			 *   X7 = 0 -> entry, = 1 -> exit
>>>> +			 */
>>>> +			saved_reg = regs->regs[7];
>>>> +			regs->regs[7] = dir;
>>>> +		}
>>>>
>>>> -	if (dir)
>>>> -		tracehook_report_syscall_exit(regs, 0);
>>>> -	else if (tracehook_report_syscall_entry(regs))
>>>> -		regs->syscallno = ~0UL;
>>>> +		if (dir)
>>>> +			tracehook_report_syscall_exit(regs, 0);
>>>> +		else if (tracehook_report_syscall_entry(regs))
>>>> +			regs->syscallno = ~0UL;
>>>>
>>>> -	if (is_compat_task())
>>>> -		regs->regs[12] = saved_reg;
>>>> -	else
>>>> -		regs->regs[7] = saved_reg;
>>>> +		if (is_compat_task())
>>>> +			regs->regs[12] = saved_reg;
>>>> +		else
>>>> +			regs->regs[7] = saved_reg;
>>>> +	}
>>>
>>> Aren't these changes (to ptrace.c) just a giant NOP?
>>
>> Umm, the purpose of this big "if" is to run the code only if TIF_SYSCALL_TRACE is set,
>> and to make it easy to add additional hooks, audit and ftrace, around tracehook_report_*()
>> later on.
>
> The existing code already checks TIF_SYSCALL_TRACE. I'd rather you added
> this new code when it's actually nedded (e.g. when adding audit on top).

* This patch is required only if you really merge my audit and/or ftrace patch.
* Putting these changes in audit patch would impose an extra (unnecessary) dependency on ftrace patch.
* Putting them both in audit and ftrace patch would cause a conflict when applying both patches.

Even so, since I don't bother you on this minor issue, I will follow your comment and make changes on:
* arm64: make a single hook to syscall_trace() for all syscall features
* arm64: Add audit support
* arm64: Add ftrace support

-Takahiro AKASHI

> Will