OvmfPkg/OvmfXen: Creating an ELF header

This patch changes the flash device image of OvmfXen to make it look
like it's an ELF. For this, we replace the empty embedded variable store
by a binary array, which is a ELF file header.

The ELF header explain to a loader to load the binary at the address
1MB, then jump to the PVH entry point which will be created in a later
patch. The header also includes a Xen ELF note that is part of the
PVH ABI.

That patch include OvmfXenElfHeaderGenerator.c which can be use to
regenerate the ELF header, but this will be a manual step.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1689
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20190813113119.14804-6-anthony.perard@citrix.com>

3 files changed, 239 insertions, 3 deletions

diff --git a/Maintainers.txt b/Maintainers.txt
index 42ec8d54af..016523b401 100644
--- a/Maintainers.txt
+++ b/Maintainers.txt
@@ -373,6 +373,7 @@ F: OvmfPkg/Library/XenConsoleSerialPortLib/
 F: OvmfPkg/Library/XenHypercallLib/

 F: OvmfPkg/Library/XenIoMmioLib/

 F: OvmfPkg/OvmfXen.*

+F: OvmfPkg/OvmfXenElfHeaderGenerator.c

 F: OvmfPkg/PlatformPei/MemDetect.c

 F: OvmfPkg/PlatformPei/Platform.*

 F: OvmfPkg/PlatformPei/Xen.*

diff --git a/OvmfPkg/OvmfXen.fdf b/OvmfPkg/OvmfXen.fdf
index 2ceff7baa2..43c268f6cb 100644
--- a/OvmfPkg/OvmfXen.fdf
+++ b/OvmfPkg/OvmfXen.fdf
@@ -15,8 +15,8 @@
 !include OvmfPkg.fdf.inc

 

 #

-# Build the variable store and the firmware code as one unified flash device

-# image.

+# This will allow the flash device image to be recognize as an ELF, with first

+# an ELF headers, then the firmware code.

 #

 [FD.OVMF]

 BaseAddress   = $(FW_BASE_ADDRESS)

@@ -25,7 +25,102 @@ ErasePolarity = 1
 BlockSize     = $(BLOCK_SIZE)

 NumBlocks     = $(FW_BLOCKS)

 

-!include VarStore.fdf.inc

+!if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)

+0x00000000|0x0000e000

+!endif

+!if $(FD_SIZE_IN_KB) == 4096

+0x00000000|0x00040000

+!endif

+DATA = {

+  #

+  # This hex array have been generated by OvmfPkg/OvmfXenElfHeaderGenerator.c

+  # and copied manually.

+  #

+  # ELF file header

+  0x7f, 0x45, 0x4c, 0x46, # e_ident[0..3]: Magic number

+  0x01, # File class: 32-bit objects

+  0x01, # Data encoding: 2's complement, little endian

+  0x01, # File version

+  0x03, # OS ABI identification: Object uses GNU ELF extensions

+  0x00, # ABI version

+  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  # e_ident[EI_PAD...]

+  0x02, 0x00, # e_type = Executable file

+  0x03, 0x00, # e_machine = Intel 80386

+  0x01, 0x00, 0x00, 0x00, # e_version

+  0xd0, 0xff, 0x2f, 0x00, # e_entry: Entry point virtual address

+  0x34, 0x00, 0x00, 0x00, # e_phoff: Program header table file offset

+  0x00, 0x00, 0x00, 0x00, # e_shoff: Section header table file offset

+  0x00, 0x00, 0x00, 0x00, # e_flags: Processor-specific flags

+  0x34, 0x00, #    e_ehsize: ELF header size

+  0x20, 0x00, # e_phentsize: Program header table entry size

+  0x02, 0x00, #     e_phnum: Program header table entry count

+  0x00, 0x00, # e_shentsize: Section header table entry size

+  0x00, 0x00, #     e_shnum: Section header table entry count

+  0x00, 0x00, # e_shstrndx

+

+  # ELF Program segment headers

+  # - Load segment

+  0x01, 0x00, 0x00, 0x00, # p_type = Loadable program segment

+  0x00, 0x00, 0x00, 0x00, # p_offset

+  0x00, 0x00, 0x10, 0x00, # p_vaddr: Segment virtual address

+  0x00, 0x00, 0x10, 0x00, # p_paddr: Segment physical address

+  0x00, 0x00, 0x20, 0x00, # p_filesz: Segment size in file

+  0x00, 0x00, 0x20, 0x00, # p_memsz: Segment size in memory

+  0x07, 0x00, 0x00, 0x00, # p_flags = Segment is executable | writable | readable

+  0x00, 0x00, 0x00, 0x00, # p_align

+  # - ELFNOTE segment

+  0x04, 0x00, 0x00, 0x00, # p_type = PT_NOTE

+  0x74, 0x00, 0x00, 0x00, # p_offset = point to XEN_ELFNOTE_PHYS32_ENTRY below

+  0x74, 0x00, 0x10, 0x00,

+  0x74, 0x00, 0x10, 0x00,

+  0x14, 0x00, 0x00, 0x00,

+  0x14, 0x00, 0x00, 0x00,

+  0x04, 0x00, 0x00, 0x00, # p_flags = Segment is readable

+  0x00, 0x00, 0x00, 0x00,

+

+  # XEN_ELFNOTE_PHYS32_ENTRY

+  0x04, 0x00, 0x00, 0x00, # name size

+  0x04, 0x00, 0x00, 0x00, # desc size

+  0x12, 0x00, 0x00, 0x00, # type = XEN_ELFNOTE_PHYS32_ENTRY

+  0x58, 0x65, 0x6e, 0x00, # name = "Xen"

+  0xd0, 0xff, 0x2f, 0x00, # desc: PVH entry point

+  0x00

+}

+

+!if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)

+0x0000e000|0x00001000

+!endif

+!if $(FD_SIZE_IN_KB) == 4096

+0x00040000|0x00001000

+!endif

+#NV_EVENT_LOG

+

+!if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)

+0x0000f000|0x00001000

+!endif

+!if $(FD_SIZE_IN_KB) == 4096

+0x00041000|0x00001000

+!endif

+#NV_FTW_WORKING

+DATA = {

+  # EFI_FAULT_TOLERANT_WORKING_BLOCK_HEADER->Signature = gEdkiiWorkingBlockSignatureGuid         =

+  #  { 0x9e58292b, 0x7c68, 0x497d, { 0xa0, 0xce, 0x65,  0x0, 0xfd, 0x9f, 0x1b, 0x95 }}

+  0x2b, 0x29, 0x58, 0x9e, 0x68, 0x7c, 0x7d, 0x49,

+  0xa0, 0xce, 0x65,  0x0, 0xfd, 0x9f, 0x1b, 0x95,

+  # Crc:UINT32            #WorkingBlockValid:1, WorkingBlockInvalid:1, Reserved

+  0x2c, 0xaf, 0x2c, 0x64, 0xFE, 0xFF, 0xFF, 0xFF,

+  # WriteQueueSize: UINT64

+  0xE0, 0x0F, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00

+}

+

+!if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)

+0x00010000|0x00010000

+!endif

+!if $(FD_SIZE_IN_KB) == 4096

+0x00042000|0x00042000

+!endif

+#NV_FTW_SPARE

+

 

 $(VARS_SIZE)|$(FVMAIN_SIZE)

 FV = FVMAIN_COMPACT

diff --git a/OvmfPkg/OvmfXenElfHeaderGenerator.c b/OvmfPkg/OvmfXenElfHeaderGenerator.c
new file mode 100644
index 0000000000..90f0574fc6
--- /dev/null
+++ b/OvmfPkg/OvmfXenElfHeaderGenerator.c
@@ -0,0 +1,140 @@
+/** @file

+  This program generates a hex array to be manually coppied into

+  OvmfXen.fdf.

+

+  The purpose is for the flash device image to be recognize as an ELF.

+

+  Copyright (c) 2019, Citrix Systems, Inc.

+

+  SPDX-License-Identifier: BSD-2-Clause-Patent

+**/

+

+#include "elf.h"

+#include "stdio.h"

+#include "stddef.h"

+

+void print_hdr(void *s, size_t size)

+{

+  char *c = s;

+

+  while (size--) {

+    printf("0x%02hhx, ", *(c++));

+  }

+}

+

+/* Format for the XEN_ELFNOTE_PHYS32_ENTRY program segment */

+#define XEN_ELFNOTE_PHYS32_ENTRY 18

+typedef struct {

+  uint32_t name_size;

+  uint32_t desc_size;

+  uint32_t type;

+  char name[4];

+  uint32_t desc;

+} xen_elfnote_phys32_entry;

+

+int main(void)

+{

+  /* FW_SIZE */

+  size_t ovmf_blob_size = 0x00200000;

+  /* Load OVMF at 1MB when running as PVH guest */

+  uint32_t ovmf_base_address = 0x00100000;

+  /* Xen PVH entry point */

+  uint32_t ovmfxen_pvh_entry_point = ovmf_base_address + ovmf_blob_size - 0x30;

+  size_t offset_into_file = 0;

+

+  /* ELF file header */

+  Elf32_Ehdr hdr = {

+    .e_ident = ELFMAG,

+    .e_type = ET_EXEC,

+    .e_machine = EM_386,

+    .e_version = EV_CURRENT,

+    .e_entry = ovmfxen_pvh_entry_point,

+    .e_flags = R_386_NONE,

+    .e_ehsize = sizeof (hdr),

+    .e_phentsize = sizeof (Elf32_Phdr),

+  };

+  offset_into_file += sizeof (hdr);

+

+  hdr.e_ident[EI_CLASS] = ELFCLASS32;

+  hdr.e_ident[EI_DATA] = ELFDATA2LSB;

+  hdr.e_ident[EI_VERSION] = EV_CURRENT;

+  hdr.e_ident[EI_OSABI] = ELFOSABI_LINUX;

+  /* Placing program headers just after hdr */

+  hdr.e_phoff = sizeof (hdr);

+

+  /* program header */

+  Elf32_Phdr phdr_load = {

+    .p_type = PT_LOAD,

+    .p_offset = 0, /* load everything */

+    .p_paddr = ovmf_base_address,

+    .p_filesz = ovmf_blob_size,

+    .p_memsz = ovmf_blob_size,

+    .p_flags = PF_X | PF_W | PF_R,

+    .p_align = 0,

+  };

+  phdr_load.p_vaddr = phdr_load.p_paddr;

+  hdr.e_phnum += 1;

+  offset_into_file += sizeof (phdr_load);

+

+  /* Xen ELF Note. */

+

+  xen_elfnote_phys32_entry xen_elf_note = {

+    .type = XEN_ELFNOTE_PHYS32_ENTRY,

+    .name = "Xen",

+    .desc = ovmfxen_pvh_entry_point,

+    .name_size =

+      offsetof (xen_elfnote_phys32_entry, desc) -

+      offsetof (xen_elfnote_phys32_entry, name),

+    .desc_size =

+      sizeof (xen_elfnote_phys32_entry) -

+      offsetof (xen_elfnote_phys32_entry, desc),

+  };

+  Elf32_Phdr phdr_note = {

+    .p_type = PT_NOTE,

+    .p_filesz = sizeof (xen_elf_note),

+    .p_memsz = sizeof (xen_elf_note),

+    .p_flags = PF_R,

+    .p_align = 0,

+  };

+  hdr.e_phnum += 1;

+  offset_into_file += sizeof (phdr_note);

+  phdr_note.p_offset = offset_into_file;

+  phdr_note.p_paddr = ovmf_base_address + phdr_note.p_offset;

+  phdr_note.p_vaddr = phdr_note.p_paddr;

+

+

+  /*

+   * print elf header

+   */

+

+  size_t i;

+  size_t hdr_size = sizeof (hdr);

+  size_t entry_off = offsetof(typeof(hdr), e_entry);

+

+  printf("# ELF file header\n");

+  print_hdr(&hdr, entry_off);

+  printf("\n");

+  print_hdr(&hdr.e_entry, sizeof (hdr.e_entry));

+  printf(" # hdr.e_entry\n");

+  print_hdr(&hdr.e_entry + 1, hdr_size - entry_off - sizeof (hdr.e_entry));

+

+  printf("\n\n# ELF Program segment headers\n");

+  printf("# - Load segment\n");

+  for (i = 0; i < sizeof (phdr_load); i += 4) {

+    print_hdr(((char*)&phdr_load) + i, 4);

+    printf("\n");

+  }

+  printf("# - ELFNOTE segment\n");

+  for (i = 0; i < sizeof (phdr_note); i += 4) {

+    print_hdr(((char*)&phdr_note) + i, 4);

+    printf("\n");

+  }

+

+  printf("\n# XEN_ELFNOTE_PHYS32_ENTRY\n");

+  for (i = 0; i < sizeof (xen_elf_note); i += 4) {

+    print_hdr(((char*)&xen_elf_note) + i, 4);

+    printf("\n");

+  }

+

+  return 0;

+}