Re: [PATCH 02/35] x86/cet/shstk: Add Kconfig option for Shadow Stack

Edgecombe, Rick P
2022-02-08T22:25:25Z

On Tue, 2022-02-08 at 09:41 +0100, Thomas Gleixner wrote:
> On Mon, Feb 07 2022 at 14:39, Dave Hansen wrote:
>
> > On 1/30/22 13:18, Rick Edgecombe wrote:
> > > +config X86_SHADOW_STACK
> > > + prompt "Intel Shadow Stack"
> > > + def_bool n
> > > + depends on AS_WRUSS
> > > + depends on ARCH_HAS_SHADOW_STACK
> > > + select ARCH_USES_HIGH_VMA_FLAGS
> > > + help
> > > + Shadow Stack protection is a hardware feature that detects
> > > function
> > > + return address corruption. This helps mitigate ROP
> > > attacks.
> > > + Applications must be enabled to use it, and old userspace
> > > does not
> > > + get protection "for free".
> > > + Support for this feature is present on Tiger Lake family
> > > of
> > > + processors released in 2020 or later. Enabling this
> > > feature
> > > + increases kernel text size by 3.7 KB.
> >
> > I guess the "2020" comment is still OK. But, given that it's on
> > AMD and
> > a could of other Intel models, maybe we should just leave this at:
> >
> > CPUs supporting shadow stacks were first released in 2020.
>
> Yes.
>
> > If we say anything. We mostly want folks to just go read the
> > documentation if they needs more details.
>
> Also the kernel text size increase blurb is pretty useless as that's
> a
> number which is wrong from day one.

Makes sense. Thanks.