Re: [PATCH v6 5/9] kernel: Implement selective syscall userspace redirection

On Fri, Sep 04, 2020 at 04:31:43PM -0400, Gabriel Krisman Bertazi wrote:

+int set_syscall_user_dispatch(int mode, unsigned long dispatcher_start,

• 	      unsigned long dispatcher_end, char __user *selector)
  

+{

• switch (mode) {
• case PR_SYS_DISPATCH_OFF:

...

• case PR_SYS_DISPATCH_ON:

...

• default:

• return -EINVAL;
  

...

• case PR_SET_SYSCALL_USER_DISPATCH:

• error = set_syscall_user_dispatch((int) arg2, arg3, arg4,
  

• 				  (char __user *) arg5);
  

This makes aliases of DISPATCH_OFF and DISPATCH_ON every 4GB throughout the 64-bit space of arg2. I don't think that was intentional (nor desirable). I'd suggest just making 'mode' a long and dropping the cast.