Re: [PATCH v5 04/39] x86/cpufeatures: Enable CET CR4 bit for shadow stack

[Kees Cook]

On Thu, Jan 19, 2023 at 01:22:42PM -0800, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> 
> Setting CR4.CET is a prerequisite for utilizing any CET features, most of
> which also require setting MSRs.
> 
> Kernel IBT already enables the CET CR4 bit when it detects IBT HW support
> and is configured with kernel IBT. However, future patches that enable
> userspace shadow stack support will need the bit set as well. So change
> the logic to enable it in either case.
> 
> Clear MSR_IA32_U_CET in cet_disable() so that it can't live to see
> userspace in a new kexec-ed kernel that has CR4.CET set from kernel IBT.
> 
> Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
> Tested-by: John Allen <john.allen@xxxxxxx>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-- 
Kees Cook