1# SPDX-License-Identifier: GPL-2.0
2#
3# The stub may be linked into the kernel proper or into a separate boot binary,
4# but in either case, it executes before the kernel does (with MMU disabled) so
5# things like ftrace and stack-protector are likely to cause trouble if left
6# enabled, even if doing so doesn't break the build.
7#
8cflags-$(CONFIG_X86_32)		:= -march=i386
9cflags-$(CONFIG_X86_64)		:= -mcmodel=small
10cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ \
11				   -fPIC -fno-strict-aliasing -mno-red-zone \
12				   -mno-mmx -mno-sse -fshort-wchar \
13				   -Wno-pointer-sign \
14				   $(call cc-disable-warning, address-of-packed-member) \
15				   $(call cc-disable-warning, gnu) \
16				   -fno-asynchronous-unwind-tables \
17				   $(CLANG_FLAGS)
18
19# arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
20# disable the stackleak plugin
21cflags-$(CONFIG_ARM64)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
22				   -fpie $(DISABLE_STACKLEAK_PLUGIN) \
23				   $(call cc-option,-mbranch-protection=none)
24cflags-$(CONFIG_ARM)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
25				   -fno-builtin -fpic \
26				   $(call cc-option,-mno-single-pic-base)
27cflags-$(CONFIG_RISCV)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
28				   -fpic
29
30cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
31
32KBUILD_CFLAGS			:= $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
33				   -include $(srctree)/include/linux/hidden.h \
34				   -D__NO_FORTIFY \
35				   -ffreestanding \
36				   -fno-stack-protector \
37				   $(call cc-option,-fno-addrsig) \
38				   -D__DISABLE_EXPORTS
39
40#
41# struct randomization only makes sense for Linux internal types, which the EFI
42# stub code never touches, so let's turn off struct randomization for the stub
43# altogether
44#
45KBUILD_CFLAGS := $(filter-out $(RANDSTRUCT_CFLAGS), $(KBUILD_CFLAGS))
46
47# remove SCS flags from all objects in this directory
48KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
49# disable CFI
50KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_CFI), $(KBUILD_CFLAGS))
51# disable LTO
52KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))
53
54GCOV_PROFILE			:= n
55# Sanitizer runtimes are unavailable and cannot be linked here.
56KASAN_SANITIZE			:= n
57KCSAN_SANITIZE			:= n
58UBSAN_SANITIZE			:= n
59OBJECT_FILES_NON_STANDARD	:= y
60
61# Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
62KCOV_INSTRUMENT			:= n
63
64lib-y				:= efi-stub-helper.o gop.o secureboot.o tpm.o \
65				   file.o mem.o random.o randomalloc.o pci.o \
66				   skip_spaces.o lib-cmdline.o lib-ctype.o \
67				   alignedmem.o relocate.o vsprintf.o
68
69# include the stub's generic dependencies from lib/ when building for ARM/arm64
70efi-deps-y := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c
71
72$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
73	$(call if_changed_rule,cc_o_c)
74
75lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o fdt.o string.o \
76				   $(patsubst %.c,lib-%.o,$(efi-deps-y))
77
78lib-$(CONFIG_ARM)		+= arm32-stub.o
79lib-$(CONFIG_ARM64)		+= arm64-stub.o
80lib-$(CONFIG_X86)		+= x86-stub.o
81lib-$(CONFIG_RISCV)		+= riscv-stub.o
82CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
83
84# Even when -mbranch-protection=none is set, Clang will generate a
85# .note.gnu.property for code-less object files (like lib/ctype.c),
86# so work around this by explicitly removing the unwanted section.
87# https://bugs.llvm.org/show_bug.cgi?id=46480
88STUBCOPY_FLAGS-y		+= --remove-section=.note.gnu.property
89
90#
91# For x86, bootloaders like systemd-boot or grub-efi do not zero-initialize the
92# .bss section, so the .bss section of the EFI stub needs to be included in the
93# .data section of the compressed kernel to ensure initialization. Rename the
94# .bss section here so it's easy to pick out in the linker script.
95#
96STUBCOPY_FLAGS-$(CONFIG_X86)	+= --rename-section .bss=.bss.efistub,load,alloc
97STUBCOPY_RELOC-$(CONFIG_X86_32)	:= R_386_32
98STUBCOPY_RELOC-$(CONFIG_X86_64)	:= R_X86_64_64
99
100#
101# ARM discards the .data section because it disallows r/w data in the
102# decompressor. So move our .data to .data.efistub and .bss to .bss.efistub,
103# which are preserved explicitly by the decompressor linker script.
104#
105STUBCOPY_FLAGS-$(CONFIG_ARM)	+= --rename-section .data=.data.efistub	\
106				   --rename-section .bss=.bss.efistub,load,alloc
107STUBCOPY_RELOC-$(CONFIG_ARM)	:= R_ARM_ABS
108
109#
110# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
111# code indefinitely unless it is annotated as __init/__initdata/__initconst etc.
112# So let's apply the __init annotations at the section level, by prefixing
113# the section names directly. This will ensure that even all the inline string
114# literals are covered.
115# The fact that the stub and the kernel proper are essentially the same binary
116# also means that we need to be extra careful to make sure that the stub does
117# not rely on any absolute symbol references, considering that the virtual
118# kernel mapping that the linker uses is not active yet when the stub is
119# executing. So build all C dependencies of the EFI stub into libstub, and do
120# a verification pass to see if any absolute relocations exist in any of the
121# object files.
122#
123extra-y				:= $(lib-y)
124lib-y				:= $(patsubst %.o,%.stub.o,$(lib-y))
125
126STUBCOPY_FLAGS-$(CONFIG_ARM64)	+= --prefix-alloc-sections=.init \
127				   --prefix-symbols=__efistub_
128STUBCOPY_RELOC-$(CONFIG_ARM64)	:= R_AARCH64_ABS
129
130# For RISC-V, we don't need anything special other than arm64. Keep all the
131# symbols in .init section and make sure that no absolute symbols references
132# doesn't exist.
133STUBCOPY_FLAGS-$(CONFIG_RISCV)	+= --prefix-alloc-sections=.init \
134				   --prefix-symbols=__efistub_
135STUBCOPY_RELOC-$(CONFIG_RISCV)	:= R_RISCV_HI20
136
137$(obj)/%.stub.o: $(obj)/%.o FORCE
138	$(call if_changed,stubcopy)
139
140#
141# Strip debug sections and some other sections that may legally contain
142# absolute relocations, so that we can inspect the remaining sections for
143# such relocations. If none are found, regenerate the output object, but
144# this time, use objcopy and leave all sections in place.
145#
146quiet_cmd_stubcopy = STUBCPY $@
147      cmd_stubcopy =							\
148	$(STRIP) --strip-debug -o $@ $<;				\
149	if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); then		\
150		echo "$@: absolute symbol references not allowed in the EFI stub" >&2; \
151		/bin/false;						\
152	fi;								\
153	$(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@
154