Re: [PATCH v23 00/28] Control-flow Enforcement: Shadow Stack

Ingo Molnar
2021-03-17T09:18:07Z

* Yu, Yu-cheng <yu-cheng.yu@intel.com> wrote:

> On 3/16/2021 2:15 PM, Peter Zijlstra wrote:
> > On Tue, Mar 16, 2021 at 08:10:26AM -0700, Yu-cheng Yu wrote:
> > > Control-flow Enforcement (CET) is a new Intel processor feature that blocks
> > > return/jump-oriented programming attacks. Details are in "Intel 64 and
> > > IA-32 Architectures Software Developer's Manual" [1].
> > >
> > > CET can protect applications and the kernel. This series enables only
> > > application-level protection, and has three parts:
> > >
> > > - Shadow stack [2],
> > > - Indirect branch tracking [3], and
> > > - Selftests [4].
> >
> > CET is marketing; afaict SS and IBT are 100% independent and there's no
> > reason what so ever to have them share any code, let alone a Kconfig
> > knob.
>
> We used to have shadow stack and ibt under separate Kconfig options, but in
> a few places they actually share same code path, such as the XSAVES
> supervisor states and ELF header for example. Anyways I will be happy to
> make changes again if there is agreement.

I was look at:

x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states

didn't see any IBT logic - it's essentially all shadow stack state.

Which is not surprising, forward call edge integrity protection (IBT)
requires very little state, does it?

With IBT there's no nesting, no stack - the IBT state machine
basically requires the next instruction to be and ENDBR instruction,
and that's essentially it, right?

Thanks,

Ingo