Re: [PATCH 1/3] ptrace,syscall_user_dispatch: Implement Syscall User Dispatch Suspension

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Jan 09, 2023 at 10:33:46AM -0500, Gregory Price wrote:
> @@ -36,6 +37,10 @@ bool syscall_user_dispatch(struct pt_regs *regs)
>  	struct syscall_user_dispatch *sd = &current->syscall_dispatch;
>  	char state;
>  
> +	if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) &&
> +			unlikely(current->ptrace & PT_SUSPEND_SYSCALL_USER_DISPATCH))
> +		return false;
> +
>  	if (likely(instruction_pointer(regs) - sd->offset < sd->len))
>  		return false;
>  

So by making syscall_user_dispatch() return false, we'll make
syscall_trace_enter() continue to handle things, and supposedly you want
to land in ptrace_report_syscall_entry(), right?

> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 54482193e1ed..a6ad815bd4be 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -370,6 +370,11 @@ static int check_ptrace_options(unsigned long data)
>  	if (data & ~(unsigned long)PTRACE_O_MASK)
>  		return -EINVAL;
>  
> +	if (unlikely(data & PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH)) {
> +		if (!IS_ENABLED(CONFIG_CHECKPOINT_RESTART))
> +			return -EINVAL;
> +	}

Should setting this then not also depend on having
SYSCALL_WORK_SYSCALL_TRACE set? Because without that, you get 'funny'
things.