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

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Message-ID: <Y8gpZ+T/re7mEDjB@hirez.programming.kicks-ass.net>
Date:   Wed, 18 Jan 2023 18:16:23 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Gregory Price <gourry.memverge@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        krisman@...labora.com, tglx@...utronix.de, luto@...nel.org,
        oleg@...hat.com, ebiederm@...ssion.com, akpm@...ux-foundation.org,
        adobriyan@...il.com, corbet@....net, shuah@...nel.org,
        Gregory Price <gregory.price@...verge.com>
Subject: Re: [PATCH 1/3] ptrace,syscall_user_dispatch: Implement Syscall User
 Dispatch Suspension

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.