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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 <vaibhavrustagi@google.com>
Tested-by: Andreas Smas <andreas@lonelycoder.com>
Signed-off-by: Steve Wahl <steve.wahl@hpe.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: None
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: clang-built-linux@googlegroups.com
Cc: dimitri.sivanich@hpe.com
Cc: mike.travis@hpe.com
Cc: russ.anderson@hpe.com
Fixes: b059f801a9 ("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 <mingo@kernel.org>
This commit is contained in:
Steve Wahl 2019-09-05 15:23:46 -05:00 committed by Ingo Molnar
parent d41a3effbb
commit e16c2983fb
1 changed files with 19 additions and 16 deletions
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35
arch/x86/purgatory/Makefile
View File

@ -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)