linux-kernel - [PATCH v8 04/14] linkage: add macros for putting ASM functions into own sections

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Date:   Thu,  2 Dec 2021 23:32:04 +0100
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     linux-hardening@...r.kernel.org, x86@...nel.org
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Ard Biesheuvel <ardb@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Bruce Schlobohm <bruce.schlobohm@...el.com>,
        Jessica Yu <jeyu@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        Jonathan Corbet <corbet@....net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Marios Pomonis <pomonis@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-arch@...r.kernel.org, live-patching@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: [PATCH v8 04/14] linkage: add macros for putting ASM functions into own sections

With ClangLTO or -ffunction-sections (DCE, FG-KASLR), compiler
places C functions into separate sections by default.
However, this doesn't happen with ASM functions which are still
being placed into .text.
Introduce a pack of macros which generate a new unique section
for the describing function named in the same fashion
(.text.<func_name>).
This will be needed to make input .text section empty to harden
the kernel even more.

Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
---
 include/linux/linkage.h | 82 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)

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 */
+
+#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__ */
+
 #endif /* _LINUX_LINKAGE_H */
-- 
2.33.1