Commit 80ddf5ce authored by Heiko Carstens's avatar Heiko Carstens Committed by Alexander Gordeev
Browse files

s390: always build relocatable kernel 

Nathan Chancellor reported several link errors on s390 with
CONFIG_RELOCATABLE disabled, after binutils commit 906f69cf65da ("IBM
zSystems: Issue error for *DBL relocs on misaligned symbols"). The binutils
commit reveals potential miscompiles that might have happened already
before with linker script defined symbols at odd addresses.

A similar bug was recently fixed in the kernel with commit c9305b6c
("s390: fix nospec table alignments").

See https://github.com/ClangBuiltLinux/linux/issues/1747 for an analysis
from Ulich Weigand.

Therefore always build a relocatable kernel to avoid this problem. There is
hardly any use-case for non-relocatable kernels, so this shouldn't be
controversial.

Link: https://github.com/ClangBuiltLinux/linux/issues/1747


Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Reported-by: default avatarNathan Chancellor <nathan@kernel.org>
Tested-by: default avatarNathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20221030182202.2062705-1-hca@linux.ibm.com


Signed-off-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
parent 9afea696

arch/s390/Kconfig

+3 −3
Original line number Diff line number Diff line
@@ -568,8 +568,7 @@ config EXPOLINE_FULL 
endchoice



config RELOCATABLE

	bool "Build a relocatable kernel"

	default y

	def_bool y

	help

	  This builds a kernel image that retains relocation information

	  so it can be loaded at an arbitrary address.
@@ -578,10 +577,11 @@ config RELOCATABLE 
	  bootup process.

	  The relocations make the kernel image about 15% larger (compressed

	  10%), but are discarded at runtime.

	  Note: this option exists only for documentation purposes, please do

	  not remove it.



config RANDOMIZE_BASE

	bool "Randomize the address of the kernel image (KASLR)"

	depends on RELOCATABLE

	default y

	help

	  In support of Kernel Address Space Layout Randomization (KASLR),

arch/s390/Makefile

+0 −2
Original line number Diff line number Diff line
@@ -14,10 +14,8 @@ KBUILD_AFLAGS_MODULE += -fPIC 
KBUILD_CFLAGS_MODULE += -fPIC

KBUILD_AFLAGS	+= -m64

KBUILD_CFLAGS	+= -m64

ifeq ($(CONFIG_RELOCATABLE),y)

KBUILD_CFLAGS	+= -fPIE

LDFLAGS_vmlinux	:= -pie

endif

aflags_dwarf	:= -Wa,-gdwarf-2

KBUILD_AFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -D__ASSEMBLY__

ifndef CONFIG_AS_IS_LLVM

arch/s390/boot/Makefile

+1 −2
Original line number Diff line number Diff line
@@ -37,9 +37,8 @@ CFLAGS_sclp_early_core.o += -I$(srctree)/drivers/s390/char 


obj-y	:= head.o als.o startup.o mem_detect.o ipl_parm.o ipl_report.o

obj-y	+= string.o ebcdic.o sclp_early_core.o mem.o ipl_vmparm.o cmdline.o

obj-y	+= version.o pgm_check_info.o ctype.o ipl_data.o

obj-y	+= version.o pgm_check_info.o ctype.o ipl_data.o machine_kexec_reloc.o

obj-$(findstring y, $(CONFIG_PROTECTED_VIRTUALIZATION_GUEST) $(CONFIG_PGSTE))	+= uv.o

obj-$(CONFIG_RELOCATABLE)	+= machine_kexec_reloc.o

obj-$(CONFIG_RANDOMIZE_BASE)	+= kaslr.o

obj-y	+= $(if $(CONFIG_KERNEL_UNCOMPRESSED),,decompressor.o) info.o

obj-$(CONFIG_KERNEL_ZSTD) += clz_ctz.o

arch/s390/boot/startup.c

+1 −2
Original line number Diff line number Diff line
@@ -291,7 +291,6 @@ void startup_kernel(void) 


	clear_bss_section();

	copy_bootdata();

	if (IS_ENABLED(CONFIG_RELOCATABLE))

	handle_relocs(__kaslr_offset);



	if (__kaslr_offset) {