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

[Anshuman Khandual <anshuman.khandual@arm.com>]

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 ?

>  }
>  
> -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)