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

Peter Zijlstra
2021-03-23T20:51:01Z

On Fri, Mar 19, 2021 at 02:43:04PM -0700, Yu, Yu-cheng 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.
> > > In fact, I think all of this would improve is you remove the CET name
> > from all of this entirely. Put this series under CONFIG_X86_SHSTK (or
> > _SS) and use CONFIG_X86_IBT for the other one.
> >
> > Similarly with the .c file.
> >
> > All this CET business is just pure confusion.
> >
>
> What about this, we bring back CONFIG_X86_SHSTK and CONFIG_X86_IBT.
> For the CET name itself, can we change it to CFE (Control Flow Enforcement),
> or just CF?

Carry Flag :-)

> In signal handling, ELF header parsing and arch_prctl(), shadow stack and
> IBT pretty much share the same code. It is better not to split them into
> two sets of files.

Aside from redoing the UAPI we're stuck with that I suppose :/ And since
I think the CET name is all over the UAPI, you might as well keep it for
the kernel part of it as well :-(

But if there's sufficient !UAPI bits it might still make sense to also
have ibt.c and shstk.c