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Subject[PATCH 8/9] arm/build: Warn on orphan section placement
Date
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@chromium.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 db857d07114f..f1622bea987a 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 8247bc15addc..3ae2cf2e351b 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)
@@ -46,6 +47,13 @@
*(.hyp.idmap.text) \
__hyp_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) \
@@ -58,8 +66,14 @@
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 \
@@ -74,9 +88,7 @@
LOCK_TEXT \
HYPERVISOR_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 21b8b271c80d..8e9ac99a4335 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 319ccb10846a..f1c6f66e8e6c 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -8,7 +8,7 @@
#include "vmlinux-xip.lds.S"
#else

-#include <asm-generic/vmlinux.lds.h>
+#include <asm/vmlinux.lds.h>
#include <asm/cache.h>
#include <asm/thread_info.h>
#include <asm/memory.h>
@@ -16,8 +16,6 @@
#include <asm/page.h>
#include <asm/pgtable.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
--
2.20.1
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