linux-kernel - Re: [PATCH v9 03/16] arm64/ptrace: Return early for ptrace_report_syscall

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Message-ID: <1f919820-2c8e-f041-b38d-963b55c8792d@huawei.com>
Date: Mon, 8 Dec 2025 14:31:35 +0800
From: Jinjie Ruan <ruanjinjie@...wei.com>
To: Anshuman Khandual <anshuman.khandual@....com>, <catalin.marinas@....com>,
	<will@...nel.org>, <oleg@...hat.com>, <tglx@...utronix.de>,
	<peterz@...radead.org>, <luto@...nel.org>, <shuah@...nel.org>,
	<kees@...nel.org>, <wad@...omium.org>, <deller@....de>, <macro@...am.me.uk>,
	<charlie@...osinc.com>, <kevin.brodsky@....com>, <ldv@...ace.io>,
	<mark.rutland@....com>, <song@...nel.org>, <ryan.roberts@....com>,
	<ada.coupriediaz@....com>, <broonie@...nel.org>, <pengcan@...inos.cn>,
	<dvyukov@...gle.com>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v9 03/16] arm64/ptrace: Return early for
 ptrace_report_syscall_entry() error



On 2025/12/8 13:24, Anshuman Khandual wrote:
> On 04/12/25 1:51 PM, Jinjie Ruan wrote:
>> The generic entry abort the syscall_trace_enter() sequence if
>> ptrace_report_syscall_entry() errors out, but arm64 not.
>>
>> As the ptrace_report_syscall_entry() comment said, the calling arch code
>> should abort the system call and must prevent normal entry so no system
>> call is made if ptrace_report_syscall_entry() return nonzero.
>>
>> In preparation for moving arm64 over to the generic entry code,
>> return early if ptrace_report_syscall_entry() encounters an error.
>>
>> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
>> ---
>>  arch/arm64/kernel/ptrace.c | 14 +++++++++-----
>>  1 file changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index 4532e9831856..3926ce6aa268 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -2346,15 +2346,18 @@ static __always_inline unsigned long ptrace_save_reg(struct pt_regs *regs,
>>  	return saved_reg;
>>  }
>>  
>> -static void report_syscall_entry(struct pt_regs *regs)
>> +static int report_syscall_entry(struct pt_regs *regs)
>>  {
>>  	unsigned long saved_reg;
>> -	int regno;
>> +	int regno, ret;
>>  
>>  	saved_reg = ptrace_save_reg(regs, PTRACE_SYSCALL_ENTER, &regno);
>> -	if (ptrace_report_syscall_entry(regs))
>> +	ret = ptrace_report_syscall_entry(regs);
>> +	if (ret)
>>  		forget_syscall(regs);
>>  	regs->regs[regno] = saved_reg;
>> +
>> +	return ret;
>>  }
>>  
>>  static void report_syscall_exit(struct pt_regs *regs)
>> @@ -2381,10 +2384,11 @@ static void report_syscall_exit(struct pt_regs *regs)
>>  int syscall_trace_enter(struct pt_regs *regs)
>>  {
>>  	unsigned long flags = read_thread_flags();
>> +	int ret;
>>  
>>  	if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
>> -		report_syscall_entry(regs);
>> -		if (flags & _TIF_SYSCALL_EMU)
>> +		ret = report_syscall_entry(regs);
>> +		if (ret || (flags & _TIF_SYSCALL_EMU))
> 
> A small nit.
> 
> Could report_syscall_entry(regs) be checked directly in the 'if' conditional
> code block thus dropping new 'ret' altogether ?

It’s perfectly fine, but on the one hand, the upcoming refactor of the
secure_computing() patch will be able to use this ‘ret’, and on the
other, the intent of this patch is to highlight the differences from the
generic entry so we can switch over smoothly later. Simplifying it here
therefore doesn’t help much for demonstrating those differences.

> 
>>  			return NO_SYSCALL;
>>  	}
>>  
> 
>