Date:   Fri, 3 Dec 2021 10:31:30 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexander Lobakin <alexandr.lobakin@intel.com>
Cc:     linux-hardening@vger.kernel.org, x86@kernel.org,
        Jesse Brandeburg <jesse.brandeburg@intel.com>,
        Kristen Carlson Accardi <kristen@linux.intel.com>,
        Kees Cook <keescook@chromium.org>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Ard Biesheuvel <ardb@kernel.org>,
        Tony Luck <tony.luck@intel.com>,
        Bruce Schlobohm <bruce.schlobohm@intel.com>,
        Jessica Yu <jeyu@kernel.org>,
        kernel test robot <lkp@intel.com>,
        Miroslav Benes <mbenes@suse.cz>,
        Evgenii Shatokhin <eshatokhin@virtuozzo.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
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        Arnd Bergmann <arnd@arndb.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Nathan Chancellor <nathan@kernel.org>,
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        linux-arch@vger.kernel.org, live-patching@vger.kernel.org,
        llvm@lists.linux.dev
Subject: Re: [PATCH v8 04/14] linkage: add macros for putting ASM functions
 into own sections
Message-ID: <Yanj8qvo3Wj4ePyV@hirez.programming.kicks-ass.net>
References: <20211202223214.72888-1-alexandr.lobakin@intel.com>
 <20211202223214.72888-5-alexandr.lobakin@intel.com>
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In-Reply-To: <20211202223214.72888-5-alexandr.lobakin@intel.com>
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On Thu, Dec 02, 2021 at 11:32:04PM +0100, Alexander Lobakin wrote:

> diff --git a/include/linux/linkage.h b/include/linux/linkage.h
> index dbf8506decca..baaab7dece08 100644
> --- a/include/linux/linkage.h
> +++ b/include/linux/linkage.h
> @@ -355,4 +355,86 @@
>  
>  #endif /* __ASSEMBLY__ */
>  
> +/*
> + * Allow ASM symbols to have their own unique sections if they are being
> + * generated by the compiler for C functions (DCE, FG-KASLR, LTO).
> + */
> +#if (defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) && !defined(MODULE)) || \
> +    (defined(CONFIG_FG_KASLR) && !defined(MODULE)) || \
> +    (defined(CONFIG_MODULE_FG_KASLR) && defined(MODULE)) || \
> +    (defined(CONFIG_LTO_CLANG))
> +
> +#define SYM_TEXT_SECTION(name)				\
> +	.pushsection .text.##name, "ax"
> +
> +#define ASM_TEXT_SECTION(name)				\
> +	".text." #name
> +
> +#define ASM_PUSH_SECTION(name)				\
> +	".pushsection .text." #name ", \"ax\""
> +
> +#else /* just .text */
> +
> +#define SYM_TEXT_SECTION(name)				\
> +	.pushsection .text, "ax"
> +
> +#define ASM_TEXT_SECTION(name)				\
> +	".text"
> +
> +#define ASM_PUSH_SECTION(name)				\
> +	".pushsection .text, \"ax\""
> +
> +#endif /* just .text */

That's terribly inconsistent, SYM_TEXT_SECTION is in fact
PUSH_TEXT_SECTION, ASM_PUSH_SECTION is in fact ASM_PUSH_TEXT_SECTION and
should be stringify(PUSH_TEXT_SECTION()) or something, and they're all
repeating that ASM_TEXT_SECTION thing :/


> +
> +#ifdef __ASSEMBLY__
> +
> +#define SYM_TEXT_END_SECTION				\
> +	.popsection
> +
> +#define SYM_FUNC_START_LOCAL_ALIAS_SECTION(name)	\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_FUNC_START_LOCAL_ALIAS(name)
> +
> +#define SYM_FUNC_START_LOCAL_SECTION(name)		\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_FUNC_START_LOCAL(name)
> +
> +#define SYM_FUNC_START_NOALIGN_SECTION(name)		\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_FUNC_START_NOALIGN(name)
> +
> +#define SYM_FUNC_START_WEAK_SECTION(name)		\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_FUNC_START_WEAK(name)
> +
> +#define SYM_FUNC_START_SECTION(name)			\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_FUNC_START(name)
> +
> +#define SYM_CODE_START_LOCAL_NOALIGN_SECTION(name)	\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_CODE_START_LOCAL_NOALIGN(name)
> +
> +#define SYM_CODE_START_NOALIGN_SECTION(name)		\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_CODE_START_NOALIGN(name)
> +
> +#define SYM_CODE_START_SECTION(name)			\
> +	SYM_TEXT_SECTION(name) ASM_NL			\
> +	SYM_CODE_START(name)
> +
> +#define SYM_FUNC_END_ALIAS_SECTION(name)		\
> +	SYM_FUNC_END_ALIAS(name) ASM_NL			\
> +	SYM_TEXT_END_SECTION
> +
> +#define SYM_FUNC_END_SECTION(name)			\
> +	SYM_FUNC_END(name) ASM_NL			\
> +	SYM_TEXT_END_SECTION
> +
> +#define SYM_CODE_END_SECTION(name)			\
> +	SYM_CODE_END(name) ASM_NL			\
> +	SYM_TEXT_END_SECTION
> +
> +#endif /* __ASSEMBLY__ */

*URGH* why do we have to have new macros for this? SYM_FUNC_START*()
already takes the name as argument.