]> git.karo-electronics.de Git - karo-tx-linux.git/commitdiff
arm64/efi: isolate EFI stub from the kernel proper
authorArd Biesheuvel <ard.biesheuvel@linaro.org>
Thu, 8 Oct 2015 19:02:04 +0000 (20:02 +0100)
committerCatalin Marinas <catalin.marinas@arm.com>
Mon, 12 Oct 2015 15:20:12 +0000 (16:20 +0100)
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>
arch/arm64/kernel/Makefile
arch/arm64/kernel/efi-entry.S
arch/arm64/kernel/head.S
arch/arm64/kernel/image.h
drivers/firmware/efi/libstub/Makefile
drivers/firmware/efi/libstub/string.c [new file with mode: 0644]

index 22dc9bc781be60d34f0285c7e7e295fe62e809dd..7b17f6245f1e27bd363789fb13ecab7a88d8b00b 100644 (file)
@@ -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
index 8ce9b0577442395df912ca934f0fca338948b4a8..a773db92908b03d325c26dba0dc5ea9c287ef49d 100644 (file)
@@ -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)
index 90d09eddd5b27368e358efd44ab552db8330d39c..28a81e948df9a01199fbc8e9bed8376fce3d0b45 100644 (file)
@@ -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)
index 8fae0756e1759bad77406b0e3c76cad64b998ae0..e083af0dd54661a5ea3ec9cf161e74894a3c74e2 100644 (file)
        _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 */
index 816dbe9f4b82e68314f5c5408b52649e4b9b4383..bca9a76cbd332bace4d303457010b64eaa3d2b5f 100644 (file)
@@ -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 (file)
index 0000000..09d5a08
--- /dev/null
@@ -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