linux-hardening - [PATCH v6 kspp-next 12/22] linkage: add macros for putting ASM functions into own sections

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Message-Id: <20210831144114.154-13-alexandr.lobakin@intel.com>
Date:   Tue, 31 Aug 2021 16:41:04 +0200
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     linux-hardening@...r.kernel.org
Cc:     "Kristen C Accardi" <kristen.c.accardi@...el.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Jessica Yu <jeyu@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marios Pomonis <pomonis@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Tony Luck <tony.luck@...el.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Lukasz Czapnik <lukasz.czapnik@...el.com>,
        "Marta A Plantykow" <marta.a.plantykow@...el.com>,
        Michal Kubiak <michal.kubiak@...el.com>,
        Michal Swiatkowski <michal.swiatkowski@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        linux-kbuild@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH v6 kspp-next 12/22] 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 | 76 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/include/linux/linkage.h b/include/linux/linkage.h
index dbf8506decca..ef8641a7dc1b 100644
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h
@@ -355,4 +355,80 @@
 
 #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 ASM_PUSH_SECTION(name)				\
+	".pushsection .text." #name
+
+#define SYM_TEXT_SECTION(name)				\
+	.pushsection .text.##name
+
+#else /* just .text */
+
+#define ASM_PUSH_SECTION(name)				\
+	".pushsection .text"
+
+#define SYM_TEXT_SECTION(name)				\
+	.pushsection .text
+
+#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 */
-- 
2.31.1