Re: [PATCH] x86/alternatives: Make FineIBT mode Kconfig selectable

[Kees Cook <keescook@chromium.org>]

On Wed, May 01, 2024 at 09:33:14AM -0700, Nathan Chancellor wrote:
> On Tue, Apr 30, 2024 at 05:02:22PM -0700, Kees Cook wrote:
> > Since FineIBT performs checking at the destination, it is weaker against
> > attacks that can construct arbitrary executable memory contents. As such,
> > some system builders want to run with FineIBT disabled by default. Allow
> > the "cfi=kcfi" boot param mode to be selectable through Kconfig via the
> > newly introduced CONFIG_CFI_AUTO_DEFAULT.
> > 
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> 
> I verified that flipping the configuration does indeed change the
> default and that 'cfi=' could still be used to override whatever choice
> was made at compile time. This patch was a perfect excuse to put my new
> CET enabled test machine to work.

Heh, yeah. I have my one lonely CET system that is only powered on for
this sort of testing too. ;)

> 
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> Tested-by: Nathan Chancellor <nathan@kernel.org>

Thanks!

> CFI_DEFAULT_AUTO reads a little bit better to me personally but I am not
> looking to get into painting today :)

I went with CFI_AUTO_DEFAULT since this seems to be our current pattern
for setting these kinds of boot param defaults. A selection of examples:

arch/Kconfig:config RANDOMIZE_KSTACK_OFFSET_DEFAULT
lib/Kconfig.debug:config CONSOLE_LOGLEVEL_DEFAULT
mm/Kconfig.debug:config DEBUG_PAGEALLOC_ENABLE_DEFAULT

-- 
Kees Cook