[PATCH v2 1/2] x86: Add support for building a multiboot2 PE binary

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

In addition to building xen.efi and xen.gz, build xen-mbi.exe. The
latter is a PE binary that can be used with a multiboot2 loader that
supports loading PE binaries.

Using this option allows the binary to be signed and verified by Shim.
This means the same xen-mbi.exe binary can then be used for BIOS boot,
UEFI Boot and UEFI boot with Secure Boot verification (all with the
convenience of GRUB2 as a bootloader).

The new binary is created by modifying xen.efi:
* Relocations are stripped since they are not needed.
* The image base address is set to 0 since it must necessarily be below
  4 GiB and the loader will relocate it anyway.
* The PE entry point is set to the multiboot2 entry point rather than
  the normal EFI entry point. This is only relevant for BIOS boot since
  for EFI boot the entry point is specified via a multiboot2 tag.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
 .gitignore                        |  2 +
 xen/Makefile                      |  1 +
 xen/arch/x86/Makefile             | 16 ++++++-
 xen/arch/x86/efi/modify-mbi-exe.c | 77 +++++++++++++++++++++++++++++++
 4 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 xen/arch/x86/efi/modify-mbi-exe.c

diff --git a/.gitignore b/.gitignore
index d8b57e32f888..e61acd574b44 100644
--- a/.gitignore
+++ b/.gitignore
@@ -256,6 +256,7 @@ xen/arch/x86/boot/*.lnk
 xen/arch/x86/efi.lds
 xen/arch/x86/efi/check.efi
 xen/arch/x86/efi/mkreloc
+xen/arch/x86/efi/modify-mbi-exe
 xen/arch/x86/include/asm/asm-macros.h
 xen/arch/*/xen.lds
 xen/arch/*/efi/boot.c
@@ -304,6 +305,7 @@ xen/suppression-list.txt
 xen/xen-syms
 xen/xen-syms.map
 xen/xen.*
+xen/xen-mbi.*
 LibVNCServer*
 
 tools/qemu-xen-dir-remote
diff --git a/xen/Makefile b/xen/Makefile
index 21832d640225..1955e1d687df 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -581,6 +581,7 @@ _clean:
                -o -name ".*.cmd" -o -name "lib.a" \) -exec rm -f {} \;
        rm -f include/asm $(TARGET) $(TARGET).gz $(TARGET)-syms 
$(TARGET)-syms.map
        rm -f $(TARGET).efi $(TARGET).efi.map $(TARGET).efi.elf 
$(TARGET).efi.stripped
+       rm -f $(TARGET)-mbi.exe
        rm -f asm-offsets.s arch/*/include/asm/asm-offsets.h
        rm -f .banner .allconfig.tmp include/xen/compile.h
        rm -rf $(objtree)/arch/*/include/generated
diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 26d87405297b..5b6b8911f1f8 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -86,6 +86,7 @@ extra-y += xen.lds
 
 hostprogs-y += boot/mkelf32
 hostprogs-y += efi/mkreloc
+hostprogs-y += efi/modify-mbi-exe
 
 # Allows usercopy.c to include itself
 $(obj)/usercopy.o: CFLAGS-y += -iquote .
@@ -96,7 +97,7 @@ endif
 
 efi-y := $(shell if [ ! -r $(objtree)/include/xen/compile.h -o \
                       -O $(objtree)/include/xen/compile.h ]; then \
-                         echo '$(TARGET).efi'; fi) \
+                         echo '$(TARGET).efi $(TARGET)-mbi.exe'; fi) \
          $(space)
 efi-$(CONFIG_PV_SHIM_EXCLUSIVE) :=
 
@@ -123,6 +124,19 @@ syms-warn-dup-$(CONFIG_ENFORCE_UNIQUE_SYMBOLS) := 
--error-dup
 
 orphan-handling-$(call ld-option,--orphan-handling=warn) += 
--orphan-handling=warn
 
+ifeq ($(XEN_BUILD_PE),y)
+$(TARGET)-mbi.exe: $(TARGET).efi $(obj)/efi/modify-mbi-exe
+       $(OBJCOPY) --remove-section=.reloc $< $@.tmp
+       $(obj)/efi/modify-mbi-exe $@.tmp
+       $(OBJCOPY) --set-start=0x$$($(NM) -pa $@.tmp | awk '/T start$$/{print 
$$1}') $@.tmp $@.tmp2
+       mv $@.tmp2 $@
+       rm -f $@.tmp
+else
+$(TARGET)-mb.exe: FORCE
+       rm -f $@
+       echo 'PE build not supported'
+endif
+
 $(TARGET): TMP = $(dot-target).elf32
 $(TARGET): $(TARGET)-syms $(efi-y) $(obj)/boot/mkelf32
        $(obj)/boot/mkelf32 $(notes_phdrs) $(TARGET)-syms $(TMP) 
$(XEN_IMG_OFFSET) \
diff --git a/xen/arch/x86/efi/modify-mbi-exe.c 
b/xen/arch/x86/efi/modify-mbi-exe.c
new file mode 100644
index 000000000000..57af382cab4d
--- /dev/null
+++ b/xen/arch/x86/efi/modify-mbi-exe.c
@@ -0,0 +1,77 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+struct mz_hdr {
+    uint16_t signature;
+#define MZ_SIGNATURE 0x5a4d
+    uint16_t last_page_size;
+    uint16_t page_count;
+    uint16_t relocation_count;
+    uint16_t header_paras;
+    uint16_t min_paras;
+    uint16_t max_paras;
+    uint16_t entry_ss;
+    uint16_t entry_sp;
+    uint16_t checksum;
+    uint16_t entry_ip;
+    uint16_t entry_cs;
+    uint16_t relocations;
+    uint16_t overlay;
+    uint8_t reserved[32];
+    uint32_t extended_header_base;
+};
+
+struct coff_hdr {
+    uint32_t signature;
+    uint16_t cpu;
+    uint16_t section_count;
+    int32_t timestamp;
+    uint32_t symbols_file_offset;
+    uint32_t symbol_count;
+    uint16_t opt_hdr_size;
+    uint16_t flags;
+};
+
+#define IMAGE_BASE_OFFSET 48
+#define NEW_IMAGE_BASE 0x0
+
+int main(int argc, char **argv)
+{
+    int fd;
+    struct mz_hdr mz_hdr;
+    const uint64_t base_addr = NEW_IMAGE_BASE;
+
+    if ( argc != 2 )
+    {
+        fprintf(stderr, "usage: %s <image>\n", argv[0]);
+        return 1;
+    }
+
+    fd = open(argv[1], O_RDWR);
+    if ( fd < 0 ||
+         read(fd, &mz_hdr, sizeof(mz_hdr)) != sizeof(mz_hdr) )
+    {
+        perror(argv[1]);
+        return 2;
+    }
+
+    if ( mz_hdr.signature != MZ_SIGNATURE ||
+         !mz_hdr.extended_header_base )
+    {
+        fprintf(stderr, "%s: Wrong DOS file format\n", argv[1]);
+        return 2;
+    }
+
+    if ( lseek(fd, mz_hdr.extended_header_base + IMAGE_BASE_OFFSET, SEEK_SET) 
< 0 ||
+         write(fd, &base_addr, sizeof(base_addr)) != sizeof(base_addr) )
+    {
+        perror(argv[1]);
+        return 3;
+    }
+
+    close(fd);
+
+    return 0;
+}
-- 
2.43.0