[Xen-devel] [PATCH v4 05/35] OvmfPkg/OvmfXen: Creating an ELF header

[Anthony PERARD <anthony.perard@citrix.com>]

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>
---

Notes:
    v4:
    - fix top-level comment style
    - Update Maintainers.txt
    
    v3:
    - added license to generate_elf_header.c
      which is renamed to OvmfPkg/OvmfXenElfHeaderGenerator.c
    - added an ELF NOTE into the header

 OvmfPkg/OvmfXen.fdf                 | 101 +++++++++++++++++++-
 OvmfPkg/OvmfXenElfHeaderGenerator.c | 140 ++++++++++++++++++++++++++++
 Maintainers.txt                     |   1 +
 3 files changed, 239 insertions(+), 3 deletions(-)
 create mode 100644 OvmfPkg/OvmfXenElfHeaderGenerator.c

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 @@ [Defines]
 !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 @@ [FD.OVMF]
 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;
+}
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.*
-- 
Anthony PERARD

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