4.18-stable review patch. If anyone has any objections, please let me know.
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From: Philipp Rudo prudo@linux.ibm.com
commit ad03b821fbc30395b72af438f5bb41676a5f891d upstream.
When the kernel is built with CONFIG_EXPOLINE=y and a compiler with indirect branch mitigation enabled the purgatory crashes. The reason for that is that the macros defined for expoline are used in mem.S. These macros define new sections (.text.__s390x_indirect_*) which are marked executable. Due to the missing linker script those sections are linked to address 0, just as the .text section. In combination with the entry point also being at address 0 this causes the purgatory load code (kernel/kexec_file.c: kexec_purgatory_setup_sechdrs) to update the entry point twice. Thus the old kernel jumps to some 'random' address causing the crash.
To fix this turn off expolines for the purgatory. There is no problem with this in this case due to the fact that the purgatory only runs once and the tlb is purged (diag 308) in the end.
Fixes: 840798a1f5299 ("s390/kexec_file: Add purgatory") Cc: stable@vger.kernel.org # 4.17 Signed-off-by: Philipp Rudo prudo@linux.ibm.com Reviewed-by: Heiko Carstens heiko.carstens@de.ibm.com Signed-off-by: Martin Schwidefsky schwidefsky@de.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/s390/purgatory/Makefile | 1 + 1 file changed, 1 insertion(+)
--- a/arch/s390/purgatory/Makefile +++ b/arch/s390/purgatory/Makefile @@ -23,6 +23,7 @@ KBUILD_CFLAGS += -Wno-pointer-sign -Wno- KBUILD_CFLAGS += -fno-zero-initialized-in-bss -fno-builtin -ffreestanding KBUILD_CFLAGS += -c -MD -Os -m64 -msoft-float KBUILD_CFLAGS += $(call cc-option,-fno-PIE) +KBUILD_AFLAGS := $(filter-out -DCC_USING_EXPOLINE,$(KBUILD_AFLAGS))
$(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE $(call if_changed,ld)