Commit e8f3010f authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Catalin Marinas
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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: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: default avatarMatt Fleming <matt.fleming@intel.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 20791846
......@@ -20,6 +20,14 @@ arm64-obj-y := debug-monitors.o entry.o irq.o fpsimd.o \
cpufeature.o alternative.o cacheinfo.o \
smp.o smp_spin_table.o topology.o
stub-obj := efi-stub.o efi-entry.o
extra-y := $(stub-obj)
stub-obj := $(patsubst %.o,%.stub.o,$(stub-obj))
OBJCOPYFLAGS := --prefix-symbols=__efistub_
$(obj)/%.stub.o: $(obj)/%.o FORCE
$(call if_changed,objcopy)
arm64-obj-$(CONFIG_COMPAT) += sys32.o kuser32.o signal32.o \
sys_compat.o entry32.o \
../../arm/kernel/opcodes.o
......@@ -32,7 +40,7 @@ arm64-obj-$(CONFIG_CPU_PM) += sleep.o suspend.o
arm64-obj-$(CONFIG_CPU_IDLE) += cpuidle.o
arm64-obj-$(CONFIG_JUMP_LABEL) += jump_label.o
arm64-obj-$(CONFIG_KGDB) += kgdb.o
arm64-obj-$(CONFIG_EFI) += efi.o efi-stub.o efi-entry.o
arm64-obj-$(CONFIG_EFI) += efi.o $(stub-obj)
arm64-obj-$(CONFIG_PCI) += pci.o
arm64-obj-$(CONFIG_ARMV8_DEPRECATED) += armv8_deprecated.o
arm64-obj-$(CONFIG_ACPI) += acpi.o
......@@ -40,7 +48,7 @@ arm64-obj-$(CONFIG_ACPI) += acpi.o
obj-y += $(arm64-obj-y) vdso/
obj-m += $(arm64-obj-m)
head-y := head.o
extra-y := $(head-y) vmlinux.lds
extra-y += $(head-y) vmlinux.lds
# vDSO - this must be built first to generate the symbol offsets
$(call objectify,$(arm64-obj-y)): $(obj)/vdso/vdso-offsets.h
......
......@@ -29,7 +29,7 @@
* we want to be. The kernel image wants to be placed at TEXT_OFFSET
* from start of RAM.
*/
ENTRY(efi_stub_entry)
ENTRY(entry)
/*
* Create a stack frame to save FP/LR with extra space
* for image_addr variable passed to efi_entry().
......@@ -86,8 +86,8 @@ ENTRY(efi_stub_entry)
* entries for the VA range of the current image, so no maintenance is
* necessary.
*/
adr x0, efi_stub_entry
adr x1, efi_stub_entry_end
adr x0, entry
adr x1, entry_end
sub x1, x1, x0
bl __flush_dcache_area
......@@ -120,5 +120,5 @@ efi_load_fail:
ldp x29, x30, [sp], #32
ret
efi_stub_entry_end:
ENDPROC(efi_stub_entry)
entry_end:
ENDPROC(entry)
......@@ -120,8 +120,8 @@ efi_head:
#endif
#ifdef CONFIG_EFI
.globl stext_offset
.set stext_offset, stext - efi_head
.globl __efistub_stext_offset
.set __efistub_stext_offset, stext - efi_head
.align 3
pe_header:
.ascii "PE"
......@@ -144,8 +144,8 @@ optional_header:
.long _end - stext // SizeOfCode
.long 0 // SizeOfInitializedData
.long 0 // SizeOfUninitializedData
.long efi_stub_entry - efi_head // AddressOfEntryPoint
.long stext_offset // BaseOfCode
.long __efistub_entry - efi_head // AddressOfEntryPoint
.long __efistub_stext_offset // BaseOfCode
extra_header_fields:
.quad 0 // ImageBase
......@@ -162,7 +162,7 @@ extra_header_fields:
.long _end - efi_head // SizeOfImage
// Everything before the kernel image is considered part of the header
.long stext_offset // SizeOfHeaders
.long __efistub_stext_offset // SizeOfHeaders
.long 0 // CheckSum
.short 0xa // Subsystem (EFI application)
.short 0 // DllCharacteristics
......@@ -207,9 +207,9 @@ section_table:
.byte 0
.byte 0 // end of 0 padding of section name
.long _end - stext // VirtualSize
.long stext_offset // VirtualAddress
.long __efistub_stext_offset // VirtualAddress
.long _edata - stext // SizeOfRawData
.long stext_offset // PointerToRawData
.long __efistub_stext_offset // PointerToRawData
.long 0 // PointerToRelocations (0 for executables)
.long 0 // PointerToLineNumbers (0 for executables)
......
......@@ -59,4 +59,31 @@
_kernel_offset_le = DATA_LE64(TEXT_OFFSET); \
_kernel_flags_le = DATA_LE64(__HEAD_FLAGS);
#ifdef CONFIG_EFI
/*
* The EFI stub has its own symbol namespace prefixed by __efistub_, to
* isolate it from the kernel proper. The following symbols are legally
* accessed by the stub, so provide some aliases to make them accessible.
* Only include data symbols here, or text symbols of functions that are
* guaranteed to be safe when executed at another offset than they were
* linked at. The routines below are all implemented in assembler in a
* position independent manner
*/
__efistub_memcmp = __pi_memcmp;
__efistub_memchr = __pi_memchr;
__efistub_memcpy = __pi_memcpy;
__efistub_memmove = __pi_memmove;
__efistub_memset = __pi_memset;
__efistub_strlen = __pi_strlen;
__efistub_strcmp = __pi_strcmp;
__efistub_strncmp = __pi_strncmp;
__efistub___flush_dcache_area = __pi___flush_dcache_area;
__efistub__text = _text;
__efistub__end = _end;
__efistub__edata = _edata;
#endif
#endif /* __ASM_IMAGE_H */
......@@ -14,6 +14,8 @@ cflags-$(CONFIG_ARM64) := $(subst -pg,,$(KBUILD_CFLAGS))
cflags-$(CONFIG_ARM) := $(subst -pg,,$(KBUILD_CFLAGS)) \
-fno-builtin -fpic -mno-single-pic-base
cflags-$(CONFIG_EFI_ARMSTUB) += -I$(srctree)/scripts/dtc/libfdt
KBUILD_CFLAGS := $(cflags-y) \
$(call cc-option,-ffreestanding) \
$(call cc-option,-fno-stack-protector)
......@@ -22,7 +24,15 @@ GCOV_PROFILE := n
KASAN_SANITIZE := n
lib-y := efi-stub-helper.o
lib-$(CONFIG_EFI_ARMSTUB) += arm-stub.o fdt.o
# include the stub's generic dependencies from lib/ when building for ARM/arm64
arm-deps := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c sort.c
$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
$(call if_changed_rule,cc_o_c)
lib-$(CONFIG_EFI_ARMSTUB) += arm-stub.o fdt.o string.o \
$(patsubst %.c,lib-%.o,$(arm-deps))
#
# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
......@@ -30,10 +40,27 @@ lib-$(CONFIG_EFI_ARMSTUB) += arm-stub.o fdt.o
# So let's apply the __init annotations at the section level, by prefixing
# the section names directly. This will ensure that even all the inline string
# literals are covered.
# The fact that the stub and the kernel proper are essentially the same binary
# also means that we need to be extra careful to make sure that the stub does
# not rely on any absolute symbol references, considering that the virtual
# kernel mapping that the linker uses is not active yet when the stub is
# executing. So build all C dependencies of the EFI stub into libstub, and do
# a verification pass to see if any absolute relocations exist in any of the
# object files.
#
extra-$(CONFIG_ARM64) := $(lib-y)
lib-$(CONFIG_ARM64) := $(patsubst %.o,%.init.o,$(lib-y))
extra-$(CONFIG_EFI_ARMSTUB) := $(lib-y)
lib-$(CONFIG_EFI_ARMSTUB) := $(patsubst %.o,%.stub.o,$(lib-y))
STUBCOPY_FLAGS-y := -R .debug* -R *ksymtab*
STUBCOPY_FLAGS-$(CONFIG_ARM64) += --prefix-alloc-sections=.init \
--prefix-symbols=__efistub_
STUBCOPY_RELOC-$(CONFIG_ARM64) := R_AARCH64_ABS
$(obj)/%.stub.o: $(obj)/%.o FORCE
$(call if_changed,stubcopy)
OBJCOPYFLAGS := --prefix-alloc-sections=.init
$(obj)/%.init.o: $(obj)/%.o FORCE
$(call if_changed,objcopy)
quiet_cmd_stubcopy = STUBCPY $@
cmd_stubcopy = if $(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@; then \
$(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y) \
&& (echo >&2 "$@: absolute symbol references not allowed in the EFI stub"; \
rm -f $@; /bin/false); else /bin/false; fi
/*
* Taken from:
* linux/lib/string.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*/
#include <linux/types.h>
#include <linux/string.h>
#ifndef __HAVE_ARCH_STRSTR
/**
* strstr - Find the first substring in a %NUL terminated string
* @s1: The string to be searched
* @s2: The string to search for
*/
char *strstr(const char *s1, const char *s2)
{
size_t l1, l2;
l2 = strlen(s2);
if (!l2)
return (char *)s1;
l1 = strlen(s1);
while (l1 >= l2) {
l1--;
if (!memcmp(s1, s2, l2))
return (char *)s1;
s1++;
}
return NULL;
}
#endif
#ifndef __HAVE_ARCH_STRNCMP
/**
* strncmp - Compare two length-limited strings
* @cs: One string
* @ct: Another string
* @count: The maximum number of bytes to compare
*/
int strncmp(const char *cs, const char *ct, size_t count)
{
unsigned char c1, c2;
while (count) {
c1 = *cs++;
c2 = *ct++;
if (c1 != c2)
return c1 < c2 ? -1 : 1;
if (!c1)
break;
count--;
}
return 0;
}
#endif
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