Re: [PATCH v4 2/5] userfaultfd: add /dev/userfaultfd for fine grained access control

[Nadav Amit <namit@vmware.com>]

On Jul 19, 2022, at 12:56 PM, Axel Rasmussen <axelrasmussen@google.com> wrote:

> 
> +static int new_userfaultfd(bool is_syscall, int flags)
> {
> 	struct userfaultfd_ctx *ctx;
> 	int fd;
> 
> -	if (!sysctl_unprivileged_userfaultfd &&
> -	    (flags & UFFD_USER_MODE_ONLY) == 0 &&
> -	    !capable(CAP_SYS_PTRACE)) {
> -		printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd "
> -			"sysctl knob to 1 if kernel faults must be handled "
> -			"without obtaining CAP_SYS_PTRACE capability\n");
> +	if (is_syscall && !userfaultfd_syscall_allowed(flags))
> 		return -EPERM;
> -	}
> 
> 	BUG_ON(!current->mm);
> 
> @@ -2098,8 +2105,42 @@ SYSCALL_DEFINE1(userfaultfd, int, flags)
> 	return fd;
> }
> 
> +SYSCALL_DEFINE1(userfaultfd, int, flags)
> +{
> +	return new_userfaultfd(true, flags);
> +}

Not critical, but why not to put the userfaultfd_syscall_allowed() check
here? You would be able to lose the “is_syscall”.

I also had a small comment for patch 5.

But these are minor issues, so for the series:

Acked-by: Nadav Amit <namit@vmware.com>


[ Sorry again for misunderstanding the scheme you were using is similar to
KVM and therefore reasonable. ]