Re: [PATCH v19 02/25] x86/cet/shstk: Add Kconfig option for user-mode control-flow protection

[Yu, Yu-cheng]

On 2/4/2021 11:56 AM, Kees Cook wrote:
> On Wed, Feb 03, 2021 at 02:55:24PM -0800, Yu-cheng Yu wrote:
> > Shadow Stack provides protection against function return address
> > corruption.  It is active when the processor supports it, the kernel has
> > CONFIG_X86_CET enabled, and the application is built for the feature.
> > This is only implemented for the 64-bit kernel.  When it is enabled, legacy
> > non-Shadow Stack applications continue to work, but without protection.
> >
> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> > ---
> >   arch/x86/Kconfig           | 22 ++++++++++++++++++++++
> >   arch/x86/Kconfig.assembler |  5 +++++
> >   2 files changed, 27 insertions(+)
> >
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 21f851179ff0..074b3c0e6bf6 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -1951,6 +1951,28 @@ config X86_SGX
> >   
> >   	  If unsure, say N.
> >   
> > +config ARCH_HAS_SHADOW_STACK
> > +	def_bool n
> > +
> > +config X86_CET
> > +	prompt "Intel Control-flow protection for user-mode"
> > +	def_bool n
> > +	depends on X86_64
> > +	depends on AS_WRUSS
> > +	select ARCH_USES_HIGH_VMA_FLAGS
> > +	select ARCH_HAS_SHADOW_STACK
>
> This seems backwards to me? Shouldn't 'config X86_64' do the 'select
> ARCH_HAS_SHADOW_STACK' and 'config X86_CET' do a 'depends on
> ARCH_HAS_SHADOW_STACK' instead?

I will change it.  Thanks!

--
Yu-cheng