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

Yu, Yu-cheng
2021-03-23T21:04:43Z

On 3/23/2021 1:49 PM, Peter Zijlstra wrote:
> 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
>

I will move code around and separate it into shadow stack and ibt.
Hopefully in the next iteration, things will be more organized.

Thanks,
Yu-cheng