arm64/efi: isolate EFI stub from the kernel proper
Since arm64 does not use a builtin decompressor, the EFI stub is built into the kernel proper. So far, this has been working fine, but actually, since the stub is in fact a PE/COFF relocatable binary that is executed at an unknown offset in the 1:1 mapping provided by the UEFI firmware, we should not be seamlessly sharing code with the kernel proper, which is a position dependent executable linked at a high virtual offset. So instead, separate the contents of libstub and its dependencies, by putting them into their own namespace by prefixing all of its symbols with __efistub. This way, we have tight control over what parts of the kernel proper are referenced by the stub. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Reviewed-by: Matt Fleming <matt.fleming@intel.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Ard Biesheuvel
Catalin Marinas
parent
207918461e
commit
e8f3010f73
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@ -20,6 +20,14 @@ arm64-obj-y := debug-monitors.o entry.o irq.o fpsimd.o \
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cpufeature.o alternative.o cacheinfo.o \
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smp.o smp_spin_table.o topology.o
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stub-obj := efi-stub.o efi-entry.o
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extra-y := $(stub-obj)
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stub-obj := $(patsubst %.o,%.stub.o,$(stub-obj))
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OBJCOPYFLAGS := --prefix-symbols=__efistub_
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$(obj)/%.stub.o: $(obj)/%.o FORCE
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$(call if_changed,objcopy)
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arm64-obj-$(CONFIG_COMPAT) += sys32.o kuser32.o signal32.o \
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sys_compat.o entry32.o \
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../../arm/kernel/opcodes.o
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@ -32,7 +40,7 @@ arm64-obj-$(CONFIG_CPU_PM) += sleep.o suspend.o
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arm64-obj-$(CONFIG_CPU_IDLE) += cpuidle.o
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arm64-obj-$(CONFIG_JUMP_LABEL) += jump_label.o
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arm64-obj-$(CONFIG_KGDB) += kgdb.o
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arm64-obj-$(CONFIG_EFI) += efi.o efi-stub.o efi-entry.o
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arm64-obj-$(CONFIG_EFI) += efi.o $(stub-obj)
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arm64-obj-$(CONFIG_PCI) += pci.o
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arm64-obj-$(CONFIG_ARMV8_DEPRECATED) += armv8_deprecated.o
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arm64-obj-$(CONFIG_ACPI) += acpi.o
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@ -40,7 +48,7 @@ arm64-obj-$(CONFIG_ACPI) += acpi.o
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obj-y += $(arm64-obj-y) vdso/
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obj-m += $(arm64-obj-m)
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head-y := head.o
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extra-y := $(head-y) vmlinux.lds
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extra-y += $(head-y) vmlinux.lds
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# vDSO - this must be built first to generate the symbol offsets
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$(call objectify,$(arm64-obj-y)): $(obj)/vdso/vdso-offsets.h
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@ -29,7 +29,7 @@
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* we want to be. The kernel image wants to be placed at TEXT_OFFSET
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* from start of RAM.
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*/
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ENTRY(efi_stub_entry)
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ENTRY(entry)
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/*
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* Create a stack frame to save FP/LR with extra space
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* for image_addr variable passed to efi_entry().
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@ -86,8 +86,8 @@ ENTRY(efi_stub_entry)
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* entries for the VA range of the current image, so no maintenance is
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* necessary.
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*/
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adr x0, efi_stub_entry
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adr x1, efi_stub_entry_end
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adr x0, entry
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adr x1, entry_end
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sub x1, x1, x0
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bl __flush_dcache_area
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@ -120,5 +120,5 @@ efi_load_fail:
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ldp x29, x30, [sp], #32
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ret
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efi_stub_entry_end:
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ENDPROC(efi_stub_entry)
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entry_end:
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ENDPROC(entry)
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@ -120,8 +120,8 @@ efi_head:
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#endif
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#ifdef CONFIG_EFI
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.globl stext_offset
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.set stext_offset, stext - efi_head
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.globl __efistub_stext_offset
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.set __efistub_stext_offset, stext - efi_head
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.align 3
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pe_header:
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.ascii "PE"
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@ -144,8 +144,8 @@ optional_header:
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.long _end - stext // SizeOfCode
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.long 0 // SizeOfInitializedData
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.long 0 // SizeOfUninitializedData
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.long efi_stub_entry - efi_head // AddressOfEntryPoint
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.long stext_offset // BaseOfCode
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.long __efistub_entry - efi_head // AddressOfEntryPoint
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.long __efistub_stext_offset // BaseOfCode
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extra_header_fields:
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.quad 0 // ImageBase
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@ -162,7 +162,7 @@ extra_header_fields:
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.long _end - efi_head // SizeOfImage
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// Everything before the kernel image is considered part of the header
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.long stext_offset // SizeOfHeaders
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.long __efistub_stext_offset // SizeOfHeaders
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.long 0 // CheckSum
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.short 0xa // Subsystem (EFI application)
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.short 0 // DllCharacteristics
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@ -207,9 +207,9 @@ section_table:
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.byte 0
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.byte 0 // end of 0 padding of section name
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.long _end - stext // VirtualSize
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.long stext_offset // VirtualAddress
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.long __efistub_stext_offset // VirtualAddress
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.long _edata - stext // SizeOfRawData
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.long stext_offset // PointerToRawData
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.long __efistub_stext_offset // PointerToRawData
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.long 0 // PointerToRelocations (0 for executables)
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.long 0 // PointerToLineNumbers (0 for executables)
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@ -59,4 +59,31 @@
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_kernel_offset_le = DATA_LE64(TEXT_OFFSET); \
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_kernel_flags_le = DATA_LE64(__HEAD_FLAGS);
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#ifdef CONFIG_EFI
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/*
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* The EFI stub has its own symbol namespace prefixed by __efistub_, to
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* isolate it from the kernel proper. The following symbols are legally
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* accessed by the stub, so provide some aliases to make them accessible.
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* Only include data symbols here, or text symbols of functions that are
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* guaranteed to be safe when executed at another offset than they were
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* linked at. The routines below are all implemented in assembler in a
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* position independent manner
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*/
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__efistub_memcmp = __pi_memcmp;
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__efistub_memchr = __pi_memchr;
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__efistub_memcpy = __pi_memcpy;
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__efistub_memmove = __pi_memmove;
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__efistub_memset = __pi_memset;
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__efistub_strlen = __pi_strlen;
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__efistub_strcmp = __pi_strcmp;
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__efistub_strncmp = __pi_strncmp;
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__efistub___flush_dcache_area = __pi___flush_dcache_area;
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__efistub__text = _text;
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__efistub__end = _end;
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__efistub__edata = _edata;
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#endif
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#endif /* __ASM_IMAGE_H */
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@ -14,6 +14,8 @@ cflags-$(CONFIG_ARM64) := $(subst -pg,,$(KBUILD_CFLAGS))
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cflags-$(CONFIG_ARM) := $(subst -pg,,$(KBUILD_CFLAGS)) \
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-fno-builtin -fpic -mno-single-pic-base
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cflags-$(CONFIG_EFI_ARMSTUB) += -I$(srctree)/scripts/dtc/libfdt
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KBUILD_CFLAGS := $(cflags-y) \
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$(call cc-option,-ffreestanding) \
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$(call cc-option,-fno-stack-protector)
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@ -22,7 +24,15 @@ GCOV_PROFILE := n
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KASAN_SANITIZE := n
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lib-y := efi-stub-helper.o
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lib-$(CONFIG_EFI_ARMSTUB) += arm-stub.o fdt.o
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# include the stub's generic dependencies from lib/ when building for ARM/arm64
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arm-deps := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c sort.c
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$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
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$(call if_changed_rule,cc_o_c)
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lib-$(CONFIG_EFI_ARMSTUB) += arm-stub.o fdt.o string.o \
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$(patsubst %.c,lib-%.o,$(arm-deps))
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#
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# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
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@ -30,10 +40,27 @@ lib-$(CONFIG_EFI_ARMSTUB) += arm-stub.o fdt.o
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# So let's apply the __init annotations at the section level, by prefixing
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# the section names directly. This will ensure that even all the inline string
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# literals are covered.
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# The fact that the stub and the kernel proper are essentially the same binary
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# also means that we need to be extra careful to make sure that the stub does
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# not rely on any absolute symbol references, considering that the virtual
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# kernel mapping that the linker uses is not active yet when the stub is
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# executing. So build all C dependencies of the EFI stub into libstub, and do
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# a verification pass to see if any absolute relocations exist in any of the
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# object files.
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#
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extra-$(CONFIG_ARM64) := $(lib-y)
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lib-$(CONFIG_ARM64) := $(patsubst %.o,%.init.o,$(lib-y))
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extra-$(CONFIG_EFI_ARMSTUB) := $(lib-y)
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lib-$(CONFIG_EFI_ARMSTUB) := $(patsubst %.o,%.stub.o,$(lib-y))
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OBJCOPYFLAGS := --prefix-alloc-sections=.init
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$(obj)/%.init.o: $(obj)/%.o FORCE
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$(call if_changed,objcopy)
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STUBCOPY_FLAGS-y := -R .debug* -R *ksymtab*
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STUBCOPY_FLAGS-$(CONFIG_ARM64) += --prefix-alloc-sections=.init \
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--prefix-symbols=__efistub_
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STUBCOPY_RELOC-$(CONFIG_ARM64) := R_AARCH64_ABS
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$(obj)/%.stub.o: $(obj)/%.o FORCE
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$(call if_changed,stubcopy)
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quiet_cmd_stubcopy = STUBCPY $@
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cmd_stubcopy = if $(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@; then \
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$(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y) \
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&& (echo >&2 "$@: absolute symbol references not allowed in the EFI stub"; \
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rm -f $@; /bin/false); else /bin/false; fi
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57
drivers/firmware/efi/libstub/string.c
Normal file
57
drivers/firmware/efi/libstub/string.c
Normal file
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@ -0,0 +1,57 @@
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/*
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* Taken from:
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* linux/lib/string.c
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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*/
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#include <linux/types.h>
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#include <linux/string.h>
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#ifndef __HAVE_ARCH_STRSTR
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/**
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* strstr - Find the first substring in a %NUL terminated string
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* @s1: The string to be searched
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* @s2: The string to search for
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*/
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char *strstr(const char *s1, const char *s2)
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{
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size_t l1, l2;
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l2 = strlen(s2);
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if (!l2)
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return (char *)s1;
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l1 = strlen(s1);
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while (l1 >= l2) {
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l1--;
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if (!memcmp(s1, s2, l2))
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return (char *)s1;
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s1++;
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}
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return NULL;
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}
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#endif
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#ifndef __HAVE_ARCH_STRNCMP
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/**
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* strncmp - Compare two length-limited strings
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* @cs: One string
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* @ct: Another string
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* @count: The maximum number of bytes to compare
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*/
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int strncmp(const char *cs, const char *ct, size_t count)
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{
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unsigned char c1, c2;
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while (count) {
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c1 = *cs++;
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c2 = *ct++;
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if (c1 != c2)
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return c1 < c2 ? -1 : 1;
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if (!c1)
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break;
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count--;
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}
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return 0;
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}
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#endif
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