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

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Message-ID: <20140217173522.GD26590@mudshark.cambridge.arm.com>
Date:	Mon, 17 Feb 2014 17:35:22 +0000
From:	Will Deacon <will.deacon@....com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
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

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?

>  #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).

>  	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.

Will
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