Re: [PATCH v7 05/11] arm64/ptrace: Handle ptrace_report_syscall_entry() error

[Kevin Brodsky <kevin.brodsky@arm.com>]

On 17/11/2025 14:30, Jinjie Ruan wrote:
> The generic entry handle error of ptrace_report_syscall_entry(), but
> arm64 not.

This suggests that arm64 ignores the error completely, which isn't the
case: no syscall will be performed, but tracing will still occur as normal.

What this patch seems to be doing is to abort the _enter sequence if
ptrace_report_syscall_entry() errors out. The commit title and message
should be reworded accordingly.

> As the comment said, the calling arch code should abort the system

Which comment?

> call and must prevent normal entry so no system call is
> made if ptrace_report_syscall_entry() return nonzero.

This is already the case since we're calling forget_syscall().

> 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@huawei.com>
> ---
>  arch/arm64/kernel/ptrace.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index 95984bbf53db..707951ad5d24 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -2317,10 +2317,10 @@ enum ptrace_syscall_dir {
>  	PTRACE_SYSCALL_EXIT,
>  };
>  
> -static void report_syscall_enter(struct pt_regs *regs)
> +static int report_syscall_enter(struct pt_regs *regs)
>  {
> -	int regno;
>  	unsigned long saved_reg;
> +	int regno, ret;
>  
>  	/*
>  	 * We have some ABI weirdness here in the way that we handle syscall
> @@ -2342,9 +2342,13 @@ static void report_syscall_enter(struct pt_regs *regs)
>  	saved_reg = regs->regs[regno];
>  	regs->regs[regno] = PTRACE_SYSCALL_ENTER;
>  
> -	if (ptrace_report_syscall_entry(regs))
> +	ret = ptrace_report_syscall_entry(regs);
> +	if (ret)
>  		forget_syscall(regs);

The generic syscall_trace_enter() doesn't do this (i.e. setting
regs->syscallno to NO_SYSCALL). Is that an oversight or do we just not
need it? In principle this does have a visible effect (e.g. via
REGSET_SYSTEM_CALL).

- Kevin

> +
>  	regs->regs[regno] = saved_reg;
> +
> +	return ret;
>  }
>  
>  static void report_syscall_exit(struct pt_regs *regs)
> @@ -2374,9 +2378,11 @@ static void report_syscall_exit(struct pt_regs *regs)
>  
>  int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags)
>  {
> +	int ret;
> +
>  	if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
> -		report_syscall_enter(regs);
> -		if (flags & _TIF_SYSCALL_EMU)
> +		ret = report_syscall_enter(regs);
> +		if (ret || (flags & _TIF_SYSCALL_EMU))
>  			return NO_SYSCALL;
>  	}
>