Re: [PATCH v9 04/16] arm64/ptrace: Refactor syscall_trace_enter/exit()

[Jinjie Ruan <ruanjinjie@huawei.com>]

On 2025/12/8 13:48, Anshuman Khandual wrote:
> On 04/12/25 1:51 PM, Jinjie Ruan wrote:
>> The generic syscall entry code has the following form, which use
>> the input syscall work flag and syscall number:
>>
>> | syscall_trace_enter(struct pt_regs *regs, long syscall,
>> |		      unsigned long work)
>> |
>> | syscall_exit_work(struct pt_regs *regs, unsigned long work)
>>
>> In preparation for moving arm64 over to the generic entry code,
>> refactor syscall_trace_enter/exit() to also pass thread flags, and
>> get syscall number by syscall_get_nr() helper.
>>
>> No functional changes.
>>
>> Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
>> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
>> ---
>>  arch/arm64/include/asm/syscall.h |  4 ++--
>>  arch/arm64/kernel/ptrace.c       | 25 ++++++++++++++++---------
>>  arch/arm64/kernel/syscall.c      |  5 +++--
>>  3 files changed, 21 insertions(+), 13 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
>> index 5e4c7fc44f73..cef1d9ce6e1b 100644
>> --- a/arch/arm64/include/asm/syscall.h
>> +++ b/arch/arm64/include/asm/syscall.h
>> @@ -120,7 +120,7 @@ static inline int syscall_get_arch(struct task_struct *task)
>>  	return AUDIT_ARCH_AARCH64;
>>  }
>>  
>> -int syscall_trace_enter(struct pt_regs *regs);
>> -void syscall_trace_exit(struct pt_regs *regs);
>> +int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags);
>> +void syscall_trace_exit(struct pt_regs *regs, unsigned long flags);
>>  
>>  #endif	/* __ASM_SYSCALL_H */
>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index 3926ce6aa268..b962cbcca11d 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -2381,9 +2381,8 @@ static void report_syscall_exit(struct pt_regs *regs)
>>  	}
>>  }
>>  
>> -int syscall_trace_enter(struct pt_regs *regs)
>> +int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags)
>>  {
>> -	unsigned long flags = read_thread_flags();
>>  	int ret;
>>  
>>  	if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
>> @@ -2396,19 +2395,27 @@ int syscall_trace_enter(struct pt_regs *regs)
>>  	if (secure_computing() == -1)
>>  		return NO_SYSCALL;
>>  
>> -	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
>> -		trace_sys_enter(regs, regs->syscallno);
>> +	/* Either of the above might have changed the syscall number */
>> +	syscall = syscall_get_nr(current, regs);
>>  
>> -	audit_syscall_entry(regs->syscallno, regs->orig_x0, regs->regs[1],
>> +	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) {
>> +		trace_sys_enter(regs, syscall);
>> +
>> +		/*
>> +		 * Probes or BPF hooks in the tracepoint may have changed the
>> +		 * system call number as well.
>> +		 */
>> +		 syscall = syscall_get_nr(current, regs);
>> +	}
>> +
>> +	audit_syscall_entry(syscall, regs->orig_x0, regs->regs[1],
>>  			    regs->regs[2], regs->regs[3]);
>>  
>> -	return regs->syscallno;
>> +	return syscall;
> 
> regs->syscallno still remains unchanged even if syscall is evaluated to be different ?

No, arm64 syscall_get_nr() returns regs->syscallno, use syscall_get_nr()
helper here to get the local "syscall" is to stay consistent with the
generic entry, without any semantic change.

 23 static inline int syscall_get_nr(struct task_struct *task,
 24 >------->------->------->------- struct pt_regs *regs)
 25 {
 26 >-------return regs->syscallno;
 27 }

> 
>>  }
>>  
>> -void syscall_trace_exit(struct pt_regs *regs)
>> +void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
>>  {
>> -	unsigned long flags = read_thread_flags();
>> -
>>  	audit_syscall_exit(regs);
>>  
>>  	if (flags & _TIF_SYSCALL_TRACEPOINT)
>> diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
>> index aba7ca6bca2d..ec31f82d2e9f 100644
>> --- a/arch/arm64/kernel/syscall.c
>> +++ b/arch/arm64/kernel/syscall.c
>> @@ -124,7 +124,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
>>  		 */
>>  		if (scno == NO_SYSCALL)
>>  			syscall_set_return_value(current, regs, -ENOSYS, 0);
>> -		scno = syscall_trace_enter(regs);
>> +		scno = syscall_trace_enter(regs, scno, flags);
>>  		if (scno == NO_SYSCALL)
>>  			goto trace_exit;
>>  	}
>> @@ -143,7 +143,8 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
>>  	}
>>  
>>  trace_exit:
>> -	syscall_trace_exit(regs);
>> +	flags = read_thread_flags();
>> +	syscall_trace_exit(regs, flags);
>>  }
>>  
>>  void do_el0_svc(struct pt_regs *regs)
> 
>