linux/arch/x86/boot/Makefile
Nick Desaulniers ffcf9c5700 x86: link vdso and boot with -z noexecstack --no-warn-rwx-segments
Users of GNU ld (BFD) from binutils 2.39+ will observe multiple
instances of a new warning when linking kernels in the form:

  ld: warning: arch/x86/boot/pmjump.o: missing .note.GNU-stack section implies executable stack
  ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
  ld: warning: arch/x86/boot/compressed/vmlinux has a LOAD segment with RWX permissions

Generally, we would like to avoid the stack being executable.  Because
there could be a need for the stack to be executable, assembler sources
have to opt-in to this security feature via explicit creation of the
.note.GNU-stack feature (which compilers create by default) or command
line flag --noexecstack.  Or we can simply tell the linker the
production of such sections is irrelevant and to link the stack as
--noexecstack.

LLVM's LLD linker defaults to -z noexecstack, so this flag isn't
strictly necessary when linking with LLD, only BFD, but it doesn't hurt
to be explicit here for all linkers IMO.  --no-warn-rwx-segments is
currently BFD specific and only available in the current latest release,
so it's wrapped in an ld-option check.

While the kernel makes extensive usage of ELF sections, it doesn't use
permissions from ELF segments.

Link: https://lore.kernel.org/linux-block/3af4127a-f453-4cf7-f133-a181cce06f73@kernel.dk/
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ba951afb99912da01a6e8434126b8fac7aa75107
Link: https://github.com/llvm/llvm-project/issues/57009
Reported-and-tested-by: Jens Axboe <axboe@kernel.dk>
Suggested-by: Fangrui Song <maskray@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-08-10 18:30:09 -07:00

159 lines
5.2 KiB
Makefile

#
# arch/x86/boot/Makefile
#
# This file is subject to the terms and conditions of the GNU General Public
# License. See the file "COPYING" in the main directory of this archive
# for more details.
#
# Copyright (C) 1994 by Linus Torvalds
# Changed by many, many contributors over the years.
#
# Sanitizer runtimes are unavailable and cannot be linked for early boot code.
KASAN_SANITIZE := n
KCSAN_SANITIZE := n
OBJECT_FILES_NON_STANDARD := y
# Kernel does not boot with kcov instrumentation here.
# One of the problems observed was insertion of __sanitizer_cov_trace_pc()
# callback into middle of per-cpu data enabling code. Thus the callback observed
# inconsistent state and crashed. We are interested mostly in syscall coverage,
# so boot code is not interesting anyway.
KCOV_INSTRUMENT := n
# If you want to preset the SVGA mode, uncomment the next line and
# set SVGA_MODE to whatever number you want.
# Set it to -DSVGA_MODE=NORMAL_VGA if you just want the EGA/VGA mode.
# The number is the same as you would ordinarily press at bootup.
SVGA_MODE := -DSVGA_MODE=NORMAL_VGA
targets := vmlinux.bin setup.bin setup.elf bzImage
targets += fdimage fdimage144 fdimage288 image.iso hdimage
subdir- := compressed
setup-y += a20.o bioscall.o cmdline.o copy.o cpu.o cpuflags.o cpucheck.o
setup-y += early_serial_console.o edd.o header.o main.o memory.o
setup-y += pm.o pmjump.o printf.o regs.o string.o tty.o video.o
setup-y += video-mode.o version.o
setup-$(CONFIG_X86_APM_BOOT) += apm.o
# The link order of the video-*.o modules can matter. In particular,
# video-vga.o *must* be listed first, followed by video-vesa.o.
# Hardware-specific drivers should follow in the order they should be
# probed, and video-bios.o should typically be last.
setup-y += video-vga.o
setup-y += video-vesa.o
setup-y += video-bios.o
targets += $(setup-y)
hostprogs := tools/build
hostprogs += mkcpustr
HOST_EXTRACFLAGS += -I$(srctree)/tools/include \
-include include/generated/autoconf.h \
-D__EXPORTED_HEADERS__
ifdef CONFIG_X86_FEATURE_NAMES
$(obj)/cpu.o: $(obj)/cpustr.h
quiet_cmd_cpustr = CPUSTR $@
cmd_cpustr = $(obj)/mkcpustr > $@
$(obj)/cpustr.h: $(obj)/mkcpustr FORCE
$(call if_changed,cpustr)
endif
targets += cpustr.h
# ---------------------------------------------------------------------------
KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP
KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
GCOV_PROFILE := n
UBSAN_SANITIZE := n
$(obj)/bzImage: asflags-y := $(SVGA_MODE)
quiet_cmd_image = BUILD $@
silent_redirect_image = >/dev/null
cmd_image = $(obj)/tools/build $(obj)/setup.bin $(obj)/vmlinux.bin \
$(obj)/zoffset.h $@ $($(quiet)redirect_image)
$(obj)/bzImage: $(obj)/setup.bin $(obj)/vmlinux.bin $(obj)/tools/build FORCE
$(call if_changed,image)
@$(kecho) 'Kernel: $@ is ready' ' (#'`cat .version`')'
OBJCOPYFLAGS_vmlinux.bin := -O binary -R .note -R .comment -S
$(obj)/vmlinux.bin: $(obj)/compressed/vmlinux FORCE
$(call if_changed,objcopy)
SETUP_OBJS = $(addprefix $(obj)/,$(setup-y))
sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [a-zA-Z] \(startup_32\|startup_64\|efi32_stub_entry\|efi64_stub_entry\|efi_pe_entry\|efi32_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|z_.*\)$$/\#define ZO_\2 0x\1/p'
quiet_cmd_zoffset = ZOFFSET $@
cmd_zoffset = $(NM) $< | sed -n $(sed-zoffset) > $@
targets += zoffset.h
$(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE
$(call if_changed,zoffset)
AFLAGS_header.o += -I$(objtree)/$(obj)
$(obj)/header.o: $(obj)/zoffset.h
LDFLAGS_setup.elf := -m elf_i386 -z noexecstack -T
$(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
$(call if_changed,ld)
OBJCOPYFLAGS_setup.bin := -O binary
$(obj)/setup.bin: $(obj)/setup.elf FORCE
$(call if_changed,objcopy)
$(obj)/compressed/vmlinux: FORCE
$(Q)$(MAKE) $(build)=$(obj)/compressed $@
# Set this if you want to pass append arguments to the
# bzdisk/fdimage/hdimage/isoimage kernel
FDARGS =
# Set this if you want one or more initrds included in the image
FDINITRD =
imgdeps = $(obj)/bzImage $(obj)/mtools.conf $(src)/genimage.sh
$(obj)/mtools.conf: $(src)/mtools.conf.in
sed -e 's|@OBJ@|$(obj)|g' < $< > $@
targets += mtools.conf
# genimage.sh requires bash, but it also has a bunch of other
# external dependencies.
quiet_cmd_genimage = GENIMAGE $3
cmd_genimage = $(BASH) $(srctree)/$(src)/genimage.sh $2 $3 $(obj)/bzImage \
$(obj)/mtools.conf '$(FDARGS)' $(FDINITRD)
PHONY += bzdisk fdimage fdimage144 fdimage288 hdimage isoimage
# This requires write access to /dev/fd0
# All images require syslinux to be installed; hdimage also requires
# EDK2/OVMF if the kernel is compiled with the EFI stub.
bzdisk: $(imgdeps)
$(call cmd,genimage,bzdisk,/dev/fd0)
fdimage fdimage144: $(imgdeps)
$(call cmd,genimage,fdimage144,$(obj)/fdimage)
@$(kecho) 'Kernel: $(obj)/fdimage is ready'
fdimage288: $(imgdeps)
$(call cmd,genimage,fdimage288,$(obj)/fdimage)
@$(kecho) 'Kernel: $(obj)/fdimage is ready'
hdimage: $(imgdeps)
$(call cmd,genimage,hdimage,$(obj)/hdimage)
@$(kecho) 'Kernel: $(obj)/hdimage is ready'
isoimage: $(imgdeps)
$(call cmd,genimage,isoimage,$(obj)/image.iso)
@$(kecho) 'Kernel: $(obj)/image.iso is ready'