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Date:   Tue, 18 Oct 2022 22:14:59 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     x86@kernel.org, Sami Tolvanen <samitolvanen@google.com>,
        Joao Moreira <joao@overdrivepizza.com>,
        linux-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH] x86/ibt: Implement FineIBT
Message-ID: <202210182206.8B707407@keescook>
References: <Y06rtoE9BsERG9uv@hirez.programming.kicks-ass.net>
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 <Y08E9DgGD0lPB85O@hirez.programming.kicks-ass.net>
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On Tue, Oct 18, 2022 at 09:56:36PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 18, 2022 at 11:09:13AM -0700, Kees Cook wrote:
> > > +config FINEIBT
> > > +	def_bool y
> > > +	depends on X86_KERNEL_IBT && CFI_CLANG
> > > +	select CALL_PADDING
> > 
> > To that end, can we please make this a prompted choice?
> 
> How about something like so instead?

/me throws a party :)

I can imagine the case where someone will want a CONFIG to choose the
default, but yes, I love it. Thank you!

For example:

enum cfi_mode {
	CFI_OFF = 0,
	CFI_KCFI = 1,
	CFI_FINEIBT = 2,
};

#define CFI_DEFAULT	CONFIG_CFI_MODE


choice
	prompt "CFI mode" if expert
	default CFI_MODE_FINEIBT

	config CFI_MODE_FINEIBT
		bool "FineIBT"
        config CFI_MODE_KCFI
		bool "kCFI"
	config CFI_MODE_OFF
		bool "CFI disabled"
endchoice

config CFI_MODE
	int
	default "0" if CFI_MODE_OFF
	default "1" if CFI_MODE_KCFI
	default "2"


-- 
Kees Cook