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

[Will Deacon]

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 <takahiro.akashi at linaro.org>
> Acked-by: Richard Guy Briggs <rgb at redhat.com>
> ---
>  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/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> index 720e70b..0a8b2a9 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -91,6 +91,9 @@ static inline struct thread_info *current_thread_info(void)
>  /*
>   * thread information flags:
>   *  TIF_SYSCALL_TRACE	- syscall trace active
> + *  TIF_SYSCALL_TRACEPOINT - syscall tracepoint for ftrace
> + *  TIF_SYSCALL_AUDIT	- syscall auditing
> + *  TIF_SECOMP		- syscall secure computing
>   *  TIF_SIGPENDING	- signal pending
>   *  TIF_NEED_RESCHED	- rescheduling necessary
>   *  TIF_NOTIFY_RESUME	- callback before returning to user
> @@ -101,6 +104,9 @@ static inline struct thread_info *current_thread_info(void)
>  #define TIF_NEED_RESCHED	1
>  #define TIF_NOTIFY_RESUME	2	/* callback before returning to user */
>  #define TIF_SYSCALL_TRACE	8
> +#define TIF_SYSCALL_AUDIT	9
> +#define TIF_SYSCALL_TRACEPOINT	10
> +#define TIF_SECCOMP		11
>  #define TIF_POLLING_NRFLAG	16
>  #define TIF_MEMDIE		18	/* is terminating due to OOM killer */
>  #define TIF_FREEZE		19
> @@ -112,10 +118,17 @@ static inline struct thread_info *current_thread_info(void)
>  #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
>  #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
>  #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
> +#define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
> +#define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
> +#define _TIF_SYSCALL_TRACEPOINT	(1 << TIF_SYSCALL_TRACEPOINT)
> +#define _TIF_SECCOMP		(1 << TIF_SECCOMP)
>  #define _TIF_32BIT		(1 << TIF_32BIT)
>  
>  #define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
>  				 _TIF_NOTIFY_RESUME)
>  
> +#define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
> +				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP)
> +
>  #endif /* __KERNEL__ */
>  #endif /* __ASM_THREAD_INFO_H */
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 0d7b789..6d613cd 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -630,8 +630,9 @@ 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_SYSCALL_WORK
> +	b.ne	__sys_trace
>  	adr	lr, ret_fast_syscall		// return address
>  	cmp     scno, sc_nr                     // check upper syscall limit
>  	b.hs	ni_sys

All looks fine up to here.

> 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?

Will