From e16c2983fba0fa6763e43ad10916be35e3d8dc05 Mon Sep 17 00:00:00 2001 From: Steve Wahl Date: Thu, 5 Sep 2019 15:23:46 -0500 Subject: [PATCH] x86/purgatory: Change compiler flags from -mcmodel=kernel to -mcmodel=large to fix kexec relocation errors The last change to this Makefile caused relocation errors when loading a kdump kernel. Restore -mcmodel=large (not -mcmodel=kernel), -ffreestanding, and -fno-zero-initialized-bsss, without reverting to the former practice of resetting KBUILD_CFLAGS. Purgatory.ro is a standalone binary that is not linked against the rest of the kernel. Its image is copied into an array that is linked to the kernel, and from there kexec relocates it wherever it desires. With the previous change to compiler flags, the error "kexec: Overflow in relocation type 11 value 0x11fffd000" was encountered when trying to load the crash kernel. This is from kexec code trying to relocate the purgatory.ro object. From the error message, relocation type 11 is R_X86_64_32S. The x86_64 ABI says: "The R_X86_64_32 and R_X86_64_32S relocations truncate the computed value to 32-bits. The linker must verify that the generated value for the R_X86_64_32 (R_X86_64_32S) relocation zero-extends (sign-extends) to the original 64-bit value." This type of relocation doesn't work when kexec chooses to place the purgatory binary in memory that is not reachable with 32 bit addresses. The compiler flag -mcmodel=kernel allows those type of relocations to be emitted, so revert to using -mcmodel=large as was done before. Also restore the -ffreestanding and -fno-zero-initialized-bss flags because they are appropriate for a stand alone piece of object code which doesn't explicitly zero the bss, and one other report has said undefined symbols are encountered without -ffreestanding. These identical compiler flag changes need to happen for every object that becomes part of the purgatory.ro object, so gather them together first into PURGATORY_CFLAGS_REMOVE and PURGATORY_CFLAGS, and then apply them to each of the objects that have C source. Do not apply any of these flags to kexec-purgatory.o, which is not part of the standalone object but part of the kernel proper. Tested-by: Vaibhav Rustagi Tested-by: Andreas Smas Signed-off-by: Steve Wahl Reviewed-by: Nick Desaulniers Cc: Borislav Petkov Cc: H. Peter Anvin Cc: Linus Torvalds Cc: None Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: clang-built-linux@googlegroups.com Cc: dimitri.sivanich@hpe.com Cc: mike.travis@hpe.com Cc: russ.anderson@hpe.com Fixes: b059f801a937 ("x86/purgatory: Use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS") Link: https://lkml.kernel.org/r/20190905202346.GA26595@swahl-linux Signed-off-by: Ingo Molnar --- arch/x86/purgatory/Makefile | 35 +++++++++++++++++++---------------- 1 file changed, 19 insertions(+), 16 deletions(-) diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile index 8901a1f89cf5..10fb42da0007 100644 --- a/arch/x86/purgatory/Makefile +++ b/arch/x86/purgatory/Makefile @@ -18,37 +18,40 @@ targets += purgatory.ro KASAN_SANITIZE := n KCOV_INSTRUMENT := n +# These are adjustments to the compiler flags used for objects that +# make up the standalone purgatory.ro + +PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel +PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss + # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That # in turn leaves some undefined symbols like __fentry__ in purgatory and not # sure how to relocate those. ifdef CONFIG_FUNCTION_TRACER -CFLAGS_REMOVE_sha256.o += $(CC_FLAGS_FTRACE) -CFLAGS_REMOVE_purgatory.o += $(CC_FLAGS_FTRACE) -CFLAGS_REMOVE_string.o += $(CC_FLAGS_FTRACE) -CFLAGS_REMOVE_kexec-purgatory.o += $(CC_FLAGS_FTRACE) +PURGATORY_CFLAGS_REMOVE += $(CC_FLAGS_FTRACE) endif ifdef CONFIG_STACKPROTECTOR -CFLAGS_REMOVE_sha256.o += -fstack-protector -CFLAGS_REMOVE_purgatory.o += -fstack-protector -CFLAGS_REMOVE_string.o += -fstack-protector -CFLAGS_REMOVE_kexec-purgatory.o += -fstack-protector +PURGATORY_CFLAGS_REMOVE += -fstack-protector endif ifdef CONFIG_STACKPROTECTOR_STRONG -CFLAGS_REMOVE_sha256.o += -fstack-protector-strong -CFLAGS_REMOVE_purgatory.o += -fstack-protector-strong -CFLAGS_REMOVE_string.o += -fstack-protector-strong -CFLAGS_REMOVE_kexec-purgatory.o += -fstack-protector-strong +PURGATORY_CFLAGS_REMOVE += -fstack-protector-strong endif ifdef CONFIG_RETPOLINE -CFLAGS_REMOVE_sha256.o += $(RETPOLINE_CFLAGS) -CFLAGS_REMOVE_purgatory.o += $(RETPOLINE_CFLAGS) -CFLAGS_REMOVE_string.o += $(RETPOLINE_CFLAGS) -CFLAGS_REMOVE_kexec-purgatory.o += $(RETPOLINE_CFLAGS) +PURGATORY_CFLAGS_REMOVE += $(RETPOLINE_CFLAGS) endif +CFLAGS_REMOVE_purgatory.o += $(PURGATORY_CFLAGS_REMOVE) +CFLAGS_purgatory.o += $(PURGATORY_CFLAGS) + +CFLAGS_REMOVE_sha256.o += $(PURGATORY_CFLAGS_REMOVE) +CFLAGS_sha256.o += $(PURGATORY_CFLAGS) + +CFLAGS_REMOVE_string.o += $(PURGATORY_CFLAGS_REMOVE) +CFLAGS_string.o += $(PURGATORY_CFLAGS) + $(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE $(call if_changed,ld) -- 2.30.2