On Wed, Apr 22, 2020 at 05:26:32PM -0700, Daniel Colascione wrote:
> +unprivileged_userfaultfd_user_mode_only
> +========================================
> +
> +This flag controls whether unprivileged users can use the userfaultfd
> +system calls to handle page faults in kernel mode. If set to zero,
> +userfaultfd works with or without UFFD_USER_MODE_ONLY, modulo
> +unprivileged_userfaultfd above. If set to one, users without
> +SYS_CAP_PTRACE must pass UFFD_USER_MODE_ONLY in order for userfaultfd
> +to succeed. Prohibiting use of userfaultfd for handling faults from
> +kernel mode may make certain vulnerabilities more difficult
> +to exploit.
> +
> +The default value is 0.
If this is going to be added... I am thinking whether it should be easier to
add another value for unprivileged_userfaultfd, rather than a new sysctl. E.g.:
"0": unprivileged userfaultfd forbidden
"1": unprivileged userfaultfd allowed (both user/kernel faults)
"2": unprivileged userfaultfd allowed (only user faults)
Because after all unprivileged_userfaultfd_user_mode_only will be meaningless
(iiuc) if unprivileged_userfaultfd=0. The default value will also be the same
as before ("1") then.
Thanks,
--
Peter Xu
