linux-hardening - [RFC PATCH 8/9] arm64: unwind: add asynchronous unwind tables to the kernel proper

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Message-Id: <20211013152243.2216899-9-ardb@kernel.org>
Date:   Wed, 13 Oct 2021 17:22:42 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-hardening@...r.kernel.org, mark.rutland@....com,
        catalin.marinas@....com, will@...nel.org,
        Ard Biesheuvel <ardb@...nel.org>
Subject: [RFC PATCH 8/9] arm64: unwind: add asynchronous unwind tables to the kernel proper

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/Kconfig                    |  3 +++
 arch/arm64/Makefile                   |  7 ++++++-
 arch/arm64/kernel/vmlinux.lds.S       | 20 ++++++++++++++++++++
 drivers/firmware/efi/libstub/Makefile |  1 +
 4 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 077f2ec4eeb2..742baca09343 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -350,6 +350,9 @@ config KASAN_SHADOW_OFFSET
 	default 0xeffffff800000000 if ARM64_VA_BITS_36 && KASAN_SW_TAGS
 	default 0xffffffffffffffff
 
+config UNWIND_TABLES
+	bool
+
 source "arch/arm64/Kconfig.platforms"
 
 menu "Kernel Features"
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index c744b1e7b356..95ffc4deebb0 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -10,7 +10,7 @@
 #
 # Copyright (C) 1995-2001 by Russell King
 
-LDFLAGS_vmlinux	:=--no-undefined -X
+LDFLAGS_vmlinux	:=--no-undefined -X --eh-frame-hdr
 
 ifeq ($(CONFIG_RELOCATABLE), y)
 # Pass --no-apply-dynamic-relocs to restore pre-binutils-2.27 behaviour
@@ -45,8 +45,13 @@ KBUILD_CFLAGS	+= $(call cc-option,-mabi=lp64)
 KBUILD_AFLAGS	+= $(call cc-option,-mabi=lp64)
 
 # Avoid generating .eh_frame* sections.
+ifneq ($(CONFIG_UNWIND_TABLES),y)
 KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables -fno-unwind-tables
 KBUILD_AFLAGS	+= -fno-asynchronous-unwind-tables -fno-unwind-tables
+else
+KBUILD_CFLAGS	+= -fasynchronous-unwind-tables
+KBUILD_AFLAGS	+= -fasynchronous-unwind-tables
+endif
 
 ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y)
 prepare: stack_protector_prepare
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index f6b1a88245db..ed3db80bf696 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -111,6 +111,21 @@ jiffies = jiffies_64;
 #define TRAMP_TEXT
 #endif
 
+#ifdef CONFIG_UNWIND_TABLES
+#define UNWIND_DATA_SECTIONS				\
+	.eh_frame_hdr : {				\
+		__eh_frame_hdr = .;			\
+		*(.eh_frame_hdr)			\
+	}						\
+	.eh_frame : {					\
+		__eh_frame_start = .;			\
+		*(.eh_frame)				\
+		__eh_frame_end = .;			\
+	}
+#else
+#define UNWIND_DATA_SECTIONS
+#endif
+
 /*
  * The size of the PE/COFF section that covers the kernel image, which
  * runs from _stext to _edata, must be a round multiple of the PE/COFF
@@ -139,6 +154,9 @@ SECTIONS
 	/DISCARD/ : {
 		*(.interp .dynamic)
 		*(.dynsym .dynstr .hash .gnu.hash)
+#ifndef CONFIG_UNWIND_TABLES
+		*(.eh_frame_hdr .eh_frame)
+#endif
 	}
 
 	. = KIMAGE_VADDR;
@@ -217,6 +235,8 @@ SECTIONS
 		__alt_instructions_end = .;
 	}
 
+	UNWIND_DATA_SECTIONS
+
 	. = ALIGN(SEGMENT_ALIGN);
 	__inittext_end = .;
 	__initdata_begin = .;
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index d0537573501e..78c46638707a 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -20,6 +20,7 @@ cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ \
 # disable the stackleak plugin
 cflags-$(CONFIG_ARM64)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
 				   -fpie $(DISABLE_STACKLEAK_PLUGIN) \
+				   -fno-unwind-tables -fno-asynchronous-unwind-tables \
 				   $(call cc-option,-mbranch-protection=none)
 cflags-$(CONFIG_ARM)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
 				   -fno-builtin -fpic \
-- 
2.30.2