linux-kernel - [PATCH v2 1/2] arm/build: Warn on orphan section placement

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Date:   Mon, 22 Jun 2020 13:49:14 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Russell King <linux@...linux.org.uk>
Cc:     Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/2] arm/build: Warn on orphan section placement

We don't want to depend on the linker's orphan section placement
heuristics as these can vary between linkers, and may change between
versions. All sections need to be explicitly named in the linker
script.

Specifically, this would have made a recently fixed bug very obvious:

ld: warning: orphan section `.fixup' from `arch/arm/lib/copy_from_user.o' being placed in section `.fixup'

Refactor linker script include file for use in standard and XIP linker
scripts, as well as in the coming boot linker script changes. Add debug
sections explicitly. Create ARM_COMMON_DISCARD macro with unneeded
sections .ARM.attributes, .iplt, .rel.iplt, .igot.plt, and .modinfo.
Create ARM_STUBS_TEXT macro with missed text stub sections .vfp11_veneer,
and .v4_bx. Finally enable orphan section warning.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/arm/Makefile                             |  4 ++++
 .../arm/{kernel => include/asm}/vmlinux.lds.h | 22 ++++++++++++++-----
 arch/arm/kernel/vmlinux-xip.lds.S             |  5 ++---
 arch/arm/kernel/vmlinux.lds.S                 |  5 ++---
 4 files changed, 25 insertions(+), 11 deletions(-)
 rename arch/arm/{kernel => include/asm}/vmlinux.lds.h (92%)

diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 59fde2d598d8..e414e3732b3a 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -16,6 +16,10 @@ LDFLAGS_vmlinux	+= --be8
 KBUILD_LDFLAGS_MODULE	+= --be8
 endif
 
+# We never want expected sections to be placed heuristically by the
+# linker. All sections should be explicitly named in the linker script.
+LDFLAGS_vmlinux += --orphan-handling=warn
+
 ifeq ($(CONFIG_ARM_MODULE_PLTS),y)
 KBUILD_LDS_MODULE	+= $(srctree)/arch/arm/kernel/module.lds
 endif
diff --git a/arch/arm/kernel/vmlinux.lds.h b/arch/arm/include/asm/vmlinux.lds.h
similarity index 92%
rename from arch/arm/kernel/vmlinux.lds.h
rename to arch/arm/include/asm/vmlinux.lds.h
index 381a8e105fa5..3d88ea74f4cd 100644
--- a/arch/arm/kernel/vmlinux.lds.h
+++ b/arch/arm/include/asm/vmlinux.lds.h
@@ -1,4 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0 */
+#include <asm-generic/vmlinux.lds.h>
 
 #ifdef CONFIG_HOTPLUG_CPU
 #define ARM_CPU_DISCARD(x)
@@ -37,6 +38,13 @@
 		*(.idmap.text)						\
 		__idmap_text_end = .;					\
 
+#define ARM_COMMON_DISCARD						\
+		*(.ARM.attributes)					\
+		*(.iplt) *(.rel.iplt) *(.igot.plt)			\
+		*(.modinfo)						\
+		*(.discard)						\
+		*(.discard.*)
+
 #define ARM_DISCARD							\
 		*(.ARM.exidx.exit.text)					\
 		*(.ARM.extab.exit.text)					\
@@ -49,8 +57,14 @@
 		EXIT_CALL						\
 		ARM_MMU_DISCARD(*(.text.fixup))				\
 		ARM_MMU_DISCARD(*(__ex_table))				\
-		*(.discard)						\
-		*(.discard.*)
+		ARM_COMMON_DISCARD
+
+#define ARM_STUBS_TEXT							\
+		*(.gnu.warning)						\
+		*(.glue_7t)						\
+		*(.glue_7)						\
+		*(.vfp11_veneer)					\
+		*(.v4_bx)
 
 #define ARM_TEXT							\
 		IDMAP_TEXT						\
@@ -64,9 +78,7 @@
 		CPUIDLE_TEXT						\
 		LOCK_TEXT						\
 		KPROBES_TEXT						\
-		*(.gnu.warning)						\
-		*(.glue_7)						\
-		*(.glue_7t)						\
+		ARM_STUBS_TEXT						\
 		. = ALIGN(4);						\
 		*(.got)			/* Global offset table */	\
 		ARM_CPU_KEEP(PROC_INFO)
diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
index 6d2be994ae58..0807f40844a2 100644
--- a/arch/arm/kernel/vmlinux-xip.lds.S
+++ b/arch/arm/kernel/vmlinux-xip.lds.S
@@ -9,15 +9,13 @@
 
 #include <linux/sizes.h>
 
-#include <asm-generic/vmlinux.lds.h>
+#include <asm/vmlinux.lds.h>
 #include <asm/cache.h>
 #include <asm/thread_info.h>
 #include <asm/memory.h>
 #include <asm/mpu.h>
 #include <asm/page.h>
 
-#include "vmlinux.lds.h"
-
 OUTPUT_ARCH(arm)
 ENTRY(stext)
 
@@ -152,6 +150,7 @@ SECTIONS
 	_end = .;
 
 	STABS_DEBUG
+	DWARF_DEBUG
 }
 
 /*
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 7f24bc08403e..969205f125ca 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -9,15 +9,13 @@
 #else
 
 #include <linux/pgtable.h>
-#include <asm-generic/vmlinux.lds.h>
+#include <asm/vmlinux.lds.h>
 #include <asm/cache.h>
 #include <asm/thread_info.h>
 #include <asm/memory.h>
 #include <asm/mpu.h>
 #include <asm/page.h>
 
-#include "vmlinux.lds.h"
-
 OUTPUT_ARCH(arm)
 ENTRY(stext)
 
@@ -151,6 +149,7 @@ SECTIONS
 	_end = .;
 
 	STABS_DEBUG
+	DWARF_DEBUG
 }
 
 #ifdef CONFIG_STRICT_KERNEL_RWX
-- 
2.25.1