Skip to contentSkip to conversation

kstack_erase: Disable kstack_erase for all of arm compressed boot code

PATCH In review Kees Cook 2 participants 2 messages Jul 26, 2025 – Jul 27, 2025 Arm (32-bit)

lore
Share & tools
lore

Kees Cook

author
#0 lore raw

PATCH 1/1 kstack_erase: Disable kstack_erase for all of arm compressed boot code

When building with CONFIG_KSTACK_ERASE=y and CONFIG_ARM_ATAG_DTB_COMPAT=y, the compressed boot environment encounters an undefined symbol error:

ld.lld: error: undefined symbol: __sanitizer_cov_stack_depth >>> referenced by atags_to_fdt.c:135

This occurs because the compiler instruments the atags_to_fdt() function with sanitizer coverage calls, but the minimal compressed boot environment lacks access to sanitizer runtime support.

The compressed boot environment already disables stack protector with -fno-stack-protector. Similarly disable sanitizer coverage by adding $(DISABLE_KSTACK_ERASE) to the general compiler flags (and remove it from the one place it was noticed before), which contains the appropriate flags to prevent sanitizer instrumentation.

This follows the same pattern used in other early boot contexts where sanitizer runtime support is unavailable.

Reported-by Linux Kernel Functional Testing <[email protected]>
Closes https://lore.kernel.org/all/CA+G9fYtBk8qnpWvoaFwymCx5s5i-5KXtPGpmf=_+UKJddCOnLA@mail.gmail.com open here
Reported-by Nathan Chancellor <[email protected]>
Closes https://lore.kernel.org/all/20250726004313.GA3650901@ax162 open here
Suggested-by Nathan Chancellor <[email protected]>
Signed-off-by Kees Cook <[email protected]>
---
 arch/arm/boot/compressed/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
arch/arm/boot/compressed/Makefile +1 -1
index f9075edfd773..a159120d1e42 100644
@@ -9,7 +9,6 @@ OBJS		=
 
 HEAD	= head.o
 OBJS	+= misc.o decompress.o
-CFLAGS_decompress.o += $(DISABLE_KSTACK_ERASE)
 ifeq ($(CONFIG_DEBUG_UNCOMPRESS),y)
 OBJS	+= debug.o
 AFLAGS_head.o += -DDEBUG

@@ -96,6 +95,7 @@ KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
 
 ccflags-y := -fpic $(call cc-option,-mno-single-pic-base,) -fno-builtin \
 	     -I$(srctree)/scripts/dtc/libfdt -fno-stack-protector \
+	     $(DISABLE_KSTACK_ERASE) \
 	     -I$(obj)
 ccflags-remove-$(CONFIG_FUNCTION_TRACER) += -pg
 asflags-y := -DZIMAGE
Signature · 1 line
2.34.1
Tested-by on v1 1/1
#1 lore raw
Quoted 19 lines · Kees Cook

When building with CONFIG_KSTACK_ERASE=y and CONFIG_ARM_ATAG_DTB_COMPAT=y, the compressed boot environment encounters an undefined symbol error:

ld.lld: error: undefined symbol: __sanitizer_cov_stack_depth >>> referenced by atags_to_fdt.c:135

This occurs because the compiler instruments the atags_to_fdt() function with sanitizer coverage calls, but the minimal compressed boot environment lacks access to sanitizer runtime support.

The compressed boot environment already disables stack protector with -fno-stack-protector. Similarly disable sanitizer coverage by adding $(DISABLE_KSTACK_ERASE) to the general compiler flags (and remove it from the one place it was noticed before), which contains the appropriate flags to prevent sanitizer instrumentation.

This follows the same pattern used in other early boot contexts where sanitizer runtime support is unavailable.

Quoted 6 lines
Reported-by Linux Kernel Functional Testing <[email protected]>
Closes https://lore.kernel.org/all/CA+G9fYtBk8qnpWvoaFwymCx5s5i-5KXtPGpmf=_+UKJddCOnLA@mail.gmail.com open here
Reported-by Nathan Chancellor <[email protected]>
Closes https://lore.kernel.org/all/20250726004313.GA3650901@ax162 open here
Suggested-by Nathan Chancellor <[email protected]>
Signed-off-by Kees Cook <[email protected]>
Tested-by Nathan Chancellor <[email protected]>
Quoted 27 lines
---
 arch/arm/boot/compressed/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
arch/arm/boot/compressed/Makefile +1 -1
index f9075edfd773..a159120d1e42 100644
@@ -9,7 +9,6 @@ OBJS		=
 
 HEAD	= head.o
 OBJS	+= misc.o decompress.o
-CFLAGS_decompress.o += $(DISABLE_KSTACK_ERASE)
 ifeq ($(CONFIG_DEBUG_UNCOMPRESS),y)
 OBJS	+= debug.o
 AFLAGS_head.o += -DDEBUG

@@ -96,6 +95,7 @@ KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
 
 ccflags-y := -fpic $(call cc-option,-mno-single-pic-base,) -fno-builtin \
 	     -I$(srctree)/scripts/dtc/libfdt -fno-stack-protector \
+	     $(DISABLE_KSTACK_ERASE) \
 	     -I$(obj)
 ccflags-remove-$(CONFIG_FUNCTION_TRACER) += -pg
 asflags-y := -DZIMAGE
Signature · 1 line
2.34.1