Re: [PATCH v2 2/2] syscall_user_dispatch: add kernel.syscall_user_dispatch sysctl

[Thomas Gleixner]

On Fri, Jul 03 2026 at 21:58, Gregory Price wrote:
> --- a/kernel/entry/syscall_user_dispatch.c
> +++ b/kernel/entry/syscall_user_dispatch.c
> @@ -11,12 +11,15 @@
>  #include <linux/uaccess.h>
>  #include <linux/signal.h>
>  #include <linux/elf.h>
> +#include <linux/sysctl.h>

It's already not ordered correctly, but the rule is that we fix up the
include order to alphabetic ordering when we touch it.

>  #include <linux/sched/signal.h>
>  #include <linux/sched/task_stack.h>
>  
>  #include <asm/syscall.h>
>  
> +static int syscall_user_dispatch_allowed __read_mostly = 1;
> +
>  static void trigger_sigsys(struct pt_regs *regs)
>  {
>  	struct kernel_siginfo info;
> @@ -102,6 +105,10 @@ static int task_set_syscall_user_dispatch(struct task_struct *task, unsigned lon
>  		return -EINVAL;
>  	}
>  
> +	/* Arming can be denied at runtime via sysctl, disarming is allowed */
> +	if (mode != PR_SYS_DISPATCH_OFF && !syscall_user_dispatch_allowed)
> +		return -EPERM;
> +
>  	/*
>  	 * access_ok() will clear memory tags for tagged addresses
>  	 * if current has memory tagging enabled.
> @@ -172,3 +179,24 @@ int syscall_user_dispatch_set_config(struct task_struct *task, unsigned long siz
>  	return task_set_syscall_user_dispatch(task, cfg.mode, cfg.offset, cfg.len,
>  					      (char __user *)(uintptr_t)cfg.selector);
>  }
> +
> +#ifdef CONFIG_SYSCTL
> +static const struct ctl_table syscall_user_dispatch_sysctls[] = {
> +	{
> +		.procname	= "syscall_user_dispatch",
> +		.data		= &syscall_user_dispatch_allowed,
> +		.maxlen		= sizeof(syscall_user_dispatch_allowed),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,

proc_dobool() exists for a reason.