[PATCH v5 1/3] arm64: unwind: add asynchronous unwind tables to kernel and modules

Mon Aug 22 02:50:56 PDT 2022

Enable asynchronous unwind table generation for both the core kernel as
well as modules, and emit the resulting .eh_frame sections as init code
so we can use the unwind directives for code patching at boot or module
load time.

This will be used by dynamic shadow call stack support, which will rely
on code patching rather than compiler codegen to emit the shadow call
stack push and pop instructions.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers at google.com>
Reviewed-by: Sami Tolvanen <samitolvanen at google.com>
Tested-by: Sami Tolvanen <samitolvanen at google.com>
---
 arch/arm64/Kconfig                    |  3 +++
 arch/arm64/Makefile                   |  5 +++++
 arch/arm64/include/asm/module.lds.h   |  8 ++++++++
 arch/arm64/kernel/pi/Makefile         |  1 +
 arch/arm64/kernel/vmlinux.lds.S       | 13 +++++++++++++
 arch/arm64/kvm/hyp/nvhe/Makefile      |  1 +
 drivers/firmware/efi/libstub/Makefile |  1 +
 include/asm-generic/vmlinux.lds.h     |  9 +++++++--
 scripts/module.lds.S                  |  8 +++++++-
 9 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 571cc234d0b3..d293ac1c5b7f 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -370,6 +370,9 @@ 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 6d9d4a58b898..4fbca56fa602 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -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/include/asm/module.lds.h b/arch/arm64/include/asm/module.lds.h
index 094701ec5500..dbba4b7559aa 100644
--- a/arch/arm64/include/asm/module.lds.h
+++ b/arch/arm64/include/asm/module.lds.h
@@ -17,4 +17,12 @@ SECTIONS {
 	 */
 	.text.hot : { *(.text.hot) }
 #endif
+
+#ifdef CONFIG_UNWIND_TABLES
+	/*
+	 * Currently, we only use unwind info at module load time, so we can
+	 * put it into the .init allocation.
+	 */
+	.init.eh_frame : { *(.eh_frame) }
+#endif
 }
diff --git a/arch/arm64/kernel/pi/Makefile b/arch/arm64/kernel/pi/Makefile
index 839291430cb3..4c0ea3cd4ea4 100644
--- a/arch/arm64/kernel/pi/Makefile
+++ b/arch/arm64/kernel/pi/Makefile
@@ -7,6 +7,7 @@ KBUILD_CFLAGS	:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) -fpie \
 		   -I$(srctree)/scripts/dtc/libfdt -fno-stack-protector \
 		   -include $(srctree)/include/linux/hidden.h \
 		   -D__DISABLE_EXPORTS -ffreestanding -D__NO_FORTIFY \
+		   -fno-asynchronous-unwind-tables -fno-unwind-tables \
 		   $(call cc-option,-fno-addrsig)
 
 # remove SCS flags from all objects in this directory
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 45131e354e27..4c13dafc98b8 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -121,6 +121,17 @@ jiffies = jiffies_64;
 #define TRAMP_TEXT
 #endif
 
+#ifdef CONFIG_UNWIND_TABLES
+#define UNWIND_DATA_SECTIONS				\
+	.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
@@ -231,6 +242,8 @@ SECTIONS
 		__alt_instructions_end = .;
 	}
 
+	UNWIND_DATA_SECTIONS
+
 	. = ALIGN(SEGMENT_ALIGN);
 	__inittext_end = .;
 	__initdata_begin = .;
diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index b5c5119c7396..f566aad90875 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -89,6 +89,7 @@ quiet_cmd_hypcopy = HYPCOPY $@
 # Remove ftrace, Shadow Call Stack, and CFI CFLAGS.
 # This is equivalent to the 'notrace', '__noscs', and '__nocfi' annotations.
 KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS) $(CC_FLAGS_CFI), $(KBUILD_CFLAGS))
+KBUILD_CFLAGS += -fno-asynchronous-unwind-tables -fno-unwind-tables
 
 # KVM nVHE code is run at a different exception code with a different map, so
 # compiler instrumentation that inserts callbacks or checks into the code may
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 \
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 7515a465ec03..6d870275372b 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -1008,15 +1008,20 @@
  * keep any .init_array.* sections.
  * https://bugs.llvm.org/show_bug.cgi?id=46478
  */
+#ifdef CONFIG_UNWIND_TABLES
+#define DISCARD_EH_FRAME
+#else
+#define DISCARD_EH_FRAME	*(.eh_frame)
+#endif
 #if defined(CONFIG_GCOV_KERNEL) || defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN) || \
 	defined(CONFIG_CFI_CLANG)
 # ifdef CONFIG_CONSTRUCTORS
 #  define SANITIZER_DISCARDS						\
-	*(.eh_frame)
+	DISCARD_EH_FRAME
 # else
 #  define SANITIZER_DISCARDS						\
 	*(.init_array) *(.init_array.*)					\
-	*(.eh_frame)
+	DISCARD_EH_FRAME
 # endif
 #else
 # define SANITIZER_DISCARDS
diff --git a/scripts/module.lds.S b/scripts/module.lds.S
index 3a3aa2354ed8..9b7193d95dad 100644
--- a/scripts/module.lds.S
+++ b/scripts/module.lds.S
@@ -3,10 +3,16 @@
  * Archs are free to supply their own linker scripts.  ld will
  * combine them automatically.
  */
+#ifdef CONFIG_UNWIND_TABLES
+#define DISCARD_EH_FRAME
+#else
+#define DISCARD_EH_FRAME	*(.eh_frame)
+#endif
+
 #ifdef CONFIG_CFI_CLANG
 # include <asm/page.h>
 # define ALIGN_CFI 		ALIGN(PAGE_SIZE)
-# define SANITIZER_DISCARDS	*(.eh_frame)
+# define SANITIZER_DISCARDS	DISCARD_EH_FRAME
 #else
 # define ALIGN_CFI
 # define SANITIZER_DISCARDS
-- 
2.35.1


