[PATCH] ARM64: Provide the ARM64_TBI option

[Will Deacon]

On Wed, Jul 14, 2021 at 07:43:03PM +0100, Robin Murphy wrote:
> On 2021-07-14 19:06, Yuan Li wrote:
> > The ARM64 provides the Top Byte Ignore (TBI) early on, so the kernel turns TBI
> > on by default, but, it does not provide any option to turn the feature off.
> > 
> > In ARMv8.3, the Pointer Authentication (PA) was introduced, and if TBI is
> > turned off, the PA will be able to use the top byte, resulting longer pointer
> > authentication codes, which is more secure.
> > 
> > This patch changes the default support for the TBI to an option that can be
> > turned off.
> 
> This would have to be something that processes explicitly opt in to. See
> Documentation/arm64/tagged-pointers.rst - silently disabling TBI0 *will*
> break existing userspace software.

Maybe the patch from Peter:

https://lore.kernel.org/r/20210622051204.3682580-1-pcc@google.com

is a better starting point?

Will