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authorArd Biesheuvel <ard.biesheuvel@linaro.org>2015-10-08 20:02:04 +0100
committerCatalin Marinas <catalin.marinas@arm.com>2015-10-12 16:20:12 +0100
commite8f3010f7326c00368dbc057bd052bec80dfc072 (patch)
tree111ad1d750410588ecd346fc257c05565963f0fd /drivers/firmware
parent207918461eb0aca720fddec5da79bc71c133b9f1 (diff)
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>
Diffstat (limited to 'drivers/firmware')
-rw-r--r--drivers/firmware/efi/libstub/Makefile39
-rw-r--r--drivers/firmware/efi/libstub/string.c57
2 files changed, 90 insertions, 6 deletions
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 816dbe9f4b82..bca9a76cbd33 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -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
diff --git a/drivers/firmware/efi/libstub/string.c b/drivers/firmware/efi/libstub/string.c
new file mode 100644
index 000000000000..09d5a0894343
--- /dev/null
+++ b/drivers/firmware/efi/libstub/string.c
@@ -0,0 +1,57 @@
+/*
+ * 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