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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2026-05-14 21:38:46 +02:00
Ard Biesheuvel
7b38dec3c5
In order to be able to have tight control over which code may execute from the early 1:1 mapping of memory, but still link vmlinux as a single executable, prefix all symbol references in startup code with __pi_, and invoke it from outside using the __pi_ prefix. Use objtool to check that no absolute symbol references are present in the startup code, as these cannot be used from code running from the 1:1 mapping. Note that this also requires disabling the latent-entropy GCC plugin, as the global symbol references that it injects would require explicit exports, and given that the startup code rarely executes more than once, it is not a useful source of entropy anyway. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Link: https://lore.kernel.org/20250828102202.1849035-43-ardb+git@google.com
53 lines
1.7 KiB
Makefile
53 lines
1.7 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0
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KBUILD_AFLAGS += -D__DISABLE_EXPORTS
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KBUILD_CFLAGS += -D__DISABLE_EXPORTS -mcmodel=small -fPIC \
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-Os -DDISABLE_BRANCH_PROFILING \
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$(DISABLE_STACKLEAK_PLUGIN) \
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$(DISABLE_LATENT_ENTROPY_PLUGIN) \
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-fno-stack-protector -D__NO_FORTIFY \
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-fno-jump-tables \
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-include $(srctree)/include/linux/hidden.h
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# disable ftrace hooks and LTO
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KBUILD_CFLAGS := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS))
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KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO),$(KBUILD_CFLAGS))
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KASAN_SANITIZE := n
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KCSAN_SANITIZE := n
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KMSAN_SANITIZE := n
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UBSAN_SANITIZE := n
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KCOV_INSTRUMENT := n
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obj-$(CONFIG_X86_64) += gdt_idt.o map_kernel.o
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obj-$(CONFIG_AMD_MEM_ENCRYPT) += sme.o sev-startup.o
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pi-objs := $(patsubst %.o,$(obj)/%.o,$(obj-y))
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lib-$(CONFIG_X86_64) += la57toggle.o
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lib-$(CONFIG_EFI_MIXED) += efi-mixed.o
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#
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# Disable objtool validation for all library code, which is intended
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# to be linked into the decompressor or the EFI stub but not vmlinux
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#
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$(patsubst %.o,$(obj)/%.o,$(lib-y)): OBJECT_FILES_NON_STANDARD := y
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#
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# Invoke objtool for each object individually to check for absolute
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# relocations, even if other objtool actions are being deferred.
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#
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$(pi-objs): objtool-enabled = 1
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$(pi-objs): objtool-args = $(if $(delay-objtool),,$(objtool-args-y)) --noabs
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#
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# Confine the startup code by prefixing all symbols with __pi_ (for position
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# independent). This ensures that startup code can only call other startup
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# code, or code that has explicitly been made accessible to it via a symbol
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# alias.
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#
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$(obj)/%.pi.o: OBJCOPYFLAGS := --prefix-symbols=__pi_
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$(obj)/%.pi.o: $(obj)/%.o FORCE
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$(call if_changed,objcopy)
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targets += $(obj-y)
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obj-y := $(patsubst %.o,%.pi.o,$(obj-y))
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