linux-kernel - Re: [PATCH v2 3/6] x86/cpu: Remove CONFIG_X86

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Date:   Tue, 8 Feb 2022 18:56:40 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH v2 3/6] x86/cpu: Remove CONFIG_X86_SMAP and "nosmap"

On Tue, Feb 08, 2022 at 10:01:05PM +0100, Borislav Petkov wrote:
> On Tue, Feb 08, 2022 at 04:06:52PM +0100, Borislav Petkov wrote:
> > Hmm, I think you're right.
> > 
> > Mr. Z?
> 
> He says yes.
> 
> Ok, that was a good catch, thanks!
> 
> This chunk looks now like this - I'll send a new version later.
> 
> ---
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index a4b89b757287..404ea669ecca 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -233,7 +233,7 @@ objtool_args =								\
>  	$(if $(CONFIG_FRAME_POINTER),, --no-fp)				\
>  	$(if $(CONFIG_GCOV_KERNEL)$(CONFIG_LTO_CLANG), --no-unreachable)\
>  	$(if $(CONFIG_RETPOLINE), --retpoline)				\
> -	$(if $(CONFIG_X86_SMAP), --uaccess)				\
> +	--uaccess							\
>  	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)		\
>  	$(if $(CONFIG_SLS), --sls)
>  
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 666f7bbc13eb..0fcba46fc10f 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -106,7 +106,7 @@ modpost_link()
>  objtool_link()
>  {
>  	local objtoolcmd;
> -	local objtoolopt;
> +	local objtoolopt="--uaccess"
>  
>  	if is_enabled CONFIG_LTO_CLANG && is_enabled CONFIG_STACK_VALIDATION; then
>  		# Don't perform vmlinux validation unless explicitly requested,
> @@ -140,9 +140,6 @@ objtool_link()
>  		if is_enabled CONFIG_RETPOLINE; then
>  			objtoolopt="${objtoolopt} --retpoline"
>  		fi
> -		if is_enabled CONFIG_X86_SMAP; then
> -			objtoolopt="${objtoolopt} --uaccess"
> -		fi
>  		if is_enabled CONFIG_SLS; then
>  			objtoolopt="${objtoolopt} --sls"
>  		fi

Cool; yeah, that's kind of what I was expecting. I have a knee-jerk "I
don't want to touch this again later" reaction to seeing it always
applied instead of gated by CONFIG_X86 or something, but then, I doubt
that'll be hard to change when/if objtool becomes multi-architecture.

Consider the update as:

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook