RE: [RFC PATCH v2 2/6] x86/arch_prctl: add ARCH_GET_NOPTI and ARCH_SET_NOPTI to enable/disable PTI

[David Laight]

From: Willy Tarreau
> Sent: 09 January 2018 12:56
> 
> This allows to report the current state of the PTI protection and to
> enable or disable it for the current process. The state change is only
> allowed if the mm is not shared (no threads have been created yet).
> 
> Setting the flag to disable the protection is subject to CAP_SYS_RAWIO.
> However it is possible to re-enable the protection without this privilege.

While a process with CAP_SYS_RAWIO can easily access kernel memory so
get little extra protection from PTI, you probably want to be able
to disable PTI without giving a process CAP_SYS_RAWIO.
No point leaving the door wide open.

If you are trying to find the size of the performance hit you also
need to be able to disable (and re-enable) PTI for all the current and
future threads of a given process.

	David