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commit 09e43968db40c33a73e9ddbfd937f46d5c334924 upstream. The x86-64 psABI [0] specifies special relocation types (R_X86_64_[REX_]GOTPCRELX) for indirection through the Global Offset Table, semantically equivalent to R_X86_64_GOTPCREL, which the linker can take advantage of for optimization (relaxation) at link time. This is supported by LLD and binutils versions 2.26 onwards. The compressed kernel is position-independent code, however, when using LLD or binutils versions before 2.27, it must be linked without the -pie option. In this case, the linker may optimize certain instructions into a non-position-independent form, by converting foo@GOTPCREL(%rip) to $foo. This potential issue has been present with LLD and binutils-2.26 for a long time, but it has never manifested itself before now: - LLD and binutils-2.26 only relax movq foo@GOTPCREL(%rip), %reg to leaq foo(%rip), %reg which is still position-independent, rather than mov $foo, %reg which is permitted by the psABI when -pie is not enabled. - GCC happens to only generate GOTPCREL relocations on mov instructions. - CLang does generate GOTPCREL relocations on non-mov instructions, but when building the compressed kernel, it uses its integrated assembler (due to the redefinition of KBUILD_CFLAGS dropping -no-integrated-as), which has so far defaulted to not generating the GOTPCRELX relocations. Nick Desaulniers reports [1,2]: "A recent change [3] to a default value of configuration variable (ENABLE_X86_RELAX_RELOCATIONS OFF -> ON) in LLVM now causes Clang's integrated assembler to emit R_X86_64_GOTPCRELX/R_X86_64_REX_GOTPCRELX relocations. LLD will relax instructions with these relocations based on whether the image is being linked as position independent or not. When not, then LLD will relax these instructions to use absolute addressing mode (R_RELAX_GOT_PC_NOPIC). This causes kernels built with Clang and linked with LLD to fail to boot." Patch series [4] is a solution to allow the compressed kernel to be linked with -pie unconditionally, but even if merged is unlikely to be backported. As a simple solution that can be applied to stable as well, prevent the assembler from generating the relaxed relocation types using the -mrelax-relocations=no option. For ease of backporting, do this unconditionally. [0] https://gitlab.com/x86-psABIs/x86-64-ABI/-/blob/master/x86-64-ABI/linker-optimization.tex#L65 [1] https://lore.kernel.org/lkml/20200807194100.3570838-1-ndesaulniers@google.com/ [2] https://github.com/ClangBuiltLinux/linux/issues/1121 [3] https://reviews.llvm.org/rGc41a18cf61790fc898dcda1055c3efbf442c14c0 [4] https://lore.kernel.org/lkml/20200731202738.2577854-1-nivedita@alum.mit.edu/ Reported-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu> Signed-off-by: Ingo Molnar <mingo@kernel.org> Tested-by: Nick Desaulniers <ndesaulniers@google.com> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> Acked-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20200812004308.1448603-1-nivedita@alum.mit.edu Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
161 lines
5.6 KiB
Makefile
161 lines
5.6 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0
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#
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# linux/arch/x86/boot/compressed/Makefile
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#
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# create a compressed vmlinux image from the original vmlinux
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#
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# vmlinuz is:
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# decompression code (*.o)
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# asm globals (piggy.S), including:
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# vmlinux.bin.(gz|bz2|lzma|...)
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#
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# vmlinux.bin is:
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# vmlinux stripped of debugging and comments
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# vmlinux.bin.all is:
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# vmlinux.bin + vmlinux.relocs
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# vmlinux.bin.(gz|bz2|lzma|...) is:
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# (see scripts/Makefile.lib size_append)
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# compressed vmlinux.bin.all + u32 size of vmlinux.bin.all
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KASAN_SANITIZE := n
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OBJECT_FILES_NON_STANDARD := y
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# Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
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KCOV_INSTRUMENT := n
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targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
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vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4
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KBUILD_CFLAGS := -m$(BITS) -O2
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KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC)
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KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
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cflags-$(CONFIG_X86_32) := -march=i386
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cflags-$(CONFIG_X86_64) := -mcmodel=small
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KBUILD_CFLAGS += $(cflags-y)
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KBUILD_CFLAGS += -mno-mmx -mno-sse
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KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
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KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
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KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
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KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
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KBUILD_CFLAGS += -Wno-pointer-sign
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# Disable relocation relaxation in case the link is not PIE.
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KBUILD_CFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no)
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KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
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GCOV_PROFILE := n
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UBSAN_SANITIZE :=n
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KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
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# Compressed kernel should be built as PIE since it may be loaded at any
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# address by the bootloader.
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ifeq ($(CONFIG_X86_32),y)
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KBUILD_LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
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else
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# To build 64-bit compressed kernel as PIE, we disable relocation
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# overflow check to avoid relocation overflow error with a new linker
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# command-line option, -z noreloc-overflow.
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KBUILD_LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \
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&& echo "-z noreloc-overflow -pie --no-dynamic-linker")
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endif
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LDFLAGS_vmlinux := -T
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hostprogs-y := mkpiggy
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HOST_EXTRACFLAGS += -I$(srctree)/tools/include
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sed-voffset := -e 's/^\([0-9a-fA-F]*\) [ABCDGRSTVW] \(_text\|__bss_start\|_end\)$$/\#define VO_\2 _AC(0x\1,UL)/p'
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quiet_cmd_voffset = VOFFSET $@
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cmd_voffset = $(NM) $< | sed -n $(sed-voffset) > $@
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targets += ../voffset.h
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$(obj)/../voffset.h: vmlinux FORCE
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$(call if_changed,voffset)
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$(obj)/misc.o: $(obj)/../voffset.h
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vmlinux-objs-y := $(obj)/vmlinux.lds $(obj)/head_$(BITS).o $(obj)/misc.o \
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$(obj)/string.o $(obj)/cmdline.o $(obj)/error.o \
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$(obj)/piggy.o $(obj)/cpuflags.o
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vmlinux-objs-$(CONFIG_EARLY_PRINTK) += $(obj)/early_serial_console.o
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vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr.o
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ifdef CONFIG_X86_64
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vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr_64.o
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vmlinux-objs-y += $(obj)/mem_encrypt.o
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vmlinux-objs-y += $(obj)/pgtable_64.o
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endif
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$(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
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vmlinux-objs-$(CONFIG_EFI_STUB) += $(obj)/eboot.o $(obj)/efi_stub_$(BITS).o \
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$(objtree)/drivers/firmware/efi/libstub/lib.a
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vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
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# The compressed kernel is built with -fPIC/-fPIE so that a boot loader
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# can place it anywhere in memory and it will still run. However, since
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# it is executed as-is without any ELF relocation processing performed
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# (and has already had all relocation sections stripped from the binary),
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# none of the code can use data relocations (e.g. static assignments of
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# pointer values), since they will be meaningless at runtime. This check
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# will refuse to link the vmlinux if any of these relocations are found.
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quiet_cmd_check_data_rel = DATAREL $@
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define cmd_check_data_rel
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for obj in $(filter %.o,$^); do \
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${CROSS_COMPILE}readelf -S $$obj | grep -qF .rel.local && { \
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echo "error: $$obj has data relocations!" >&2; \
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exit 1; \
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} || true; \
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done
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endef
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# We need to run two commands under "if_changed", so merge them into a
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# single invocation.
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quiet_cmd_check-and-link-vmlinux = LD $@
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cmd_check-and-link-vmlinux = $(cmd_check_data_rel); $(cmd_ld)
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$(obj)/vmlinux: $(vmlinux-objs-y) FORCE
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$(call if_changed,check-and-link-vmlinux)
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OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
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$(obj)/vmlinux.bin: vmlinux FORCE
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$(call if_changed,objcopy)
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targets += $(patsubst $(obj)/%,%,$(vmlinux-objs-y)) vmlinux.bin.all vmlinux.relocs
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CMD_RELOCS = arch/x86/tools/relocs
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quiet_cmd_relocs = RELOCS $@
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cmd_relocs = $(CMD_RELOCS) $< > $@;$(CMD_RELOCS) --abs-relocs $<
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$(obj)/vmlinux.relocs: vmlinux FORCE
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$(call if_changed,relocs)
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vmlinux.bin.all-y := $(obj)/vmlinux.bin
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vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += $(obj)/vmlinux.relocs
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$(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE
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$(call if_changed,gzip)
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$(obj)/vmlinux.bin.bz2: $(vmlinux.bin.all-y) FORCE
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$(call if_changed,bzip2)
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$(obj)/vmlinux.bin.lzma: $(vmlinux.bin.all-y) FORCE
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$(call if_changed,lzma)
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$(obj)/vmlinux.bin.xz: $(vmlinux.bin.all-y) FORCE
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$(call if_changed,xzkern)
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$(obj)/vmlinux.bin.lzo: $(vmlinux.bin.all-y) FORCE
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$(call if_changed,lzo)
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$(obj)/vmlinux.bin.lz4: $(vmlinux.bin.all-y) FORCE
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$(call if_changed,lz4)
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suffix-$(CONFIG_KERNEL_GZIP) := gz
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suffix-$(CONFIG_KERNEL_BZIP2) := bz2
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suffix-$(CONFIG_KERNEL_LZMA) := lzma
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suffix-$(CONFIG_KERNEL_XZ) := xz
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suffix-$(CONFIG_KERNEL_LZO) := lzo
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suffix-$(CONFIG_KERNEL_LZ4) := lz4
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quiet_cmd_mkpiggy = MKPIGGY $@
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cmd_mkpiggy = $(obj)/mkpiggy $< > $@ || ( rm -f $@ ; false )
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targets += piggy.S
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$(obj)/piggy.S: $(obj)/vmlinux.bin.$(suffix-y) $(obj)/mkpiggy FORCE
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$(call if_changed,mkpiggy)
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