[PATCH] Adding Bi-Endian 32-bit and 64-bit Support to the Grub ELF Parser

[Tomohiro B Berry]

This patch adds bi-endian support for both
32-bit and 64-bit elf files.  

It compares the native endianness to the endianness of the elf file, and
swaps the header bytes if necessary.  This will allow, for example,
32-bit Big Endian grub to load a 64-bit Little Endian kernel.  

Regards,
Tomo Berry

diff --git a/grub-core/kern/elf.c b/grub-core/kern/elf.c
index 5f99c43..3326cd7 100644
--- a/grub-core/kern/elf.c
+++ b/grub-core/kern/elf.c
@@ -28,20 +28,45 @@
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
+void grub_elf32_byteswap_header (grub_elf_t
elf);
+void grub_elf64_byteswap_header (grub_elf_t
elf);
+grub_err_t grub_elf32_check_version
(grub_elf_t elf);
+grub_err_t grub_elf64_check_version
(grub_elf_t elf);
+
 /* Check if EHDR is a valid ELF
header.  */
 static grub_err_t
 grub_elf_check_header (grub_elf_t
elf)
 {
-  Elf32_Ehdr *e = &elf->ehdr.ehdr32;
+  /* e_ident is the same for both
64-bit and 32-bit so just load into a 32-bit struct for now */ 
+  Elf32_Ehdr *e = &elf->ehdr.ehdr32;
       
 
+  /* check if it is an ELF image
at all */ 
   if (e->e_ident[EI_MAG0]
!= ELFMAG0
       || e->e_ident[EI_MAG1]
!= ELFMAG1
       || e->e_ident[EI_MAG2]
!= ELFMAG2
       || e->e_ident[EI_MAG3]
!= ELFMAG3
-      || e->e_ident[EI_VERSION]
!= EV_CURRENT
-      || e->e_version
!= EV_CURRENT)
-    return grub_error (GRUB_ERR_BAD_OS,
N_("invalid arch-independent ELF magic"));
-
+      || e->e_ident[EI_VERSION]
!= EV_CURRENT)
+    return grub_error (GRUB_ERR_BAD_OS,
N_("invalid arch-independent ELF magic"));      
               
 
+  
+  switch (e->e_ident[EI_CLASS])
+    {
+      case ELFCLASS32:
+        if (e->e_ident[EI_DATA]
!= ELFDATA_NATIVE)
+          grub_elf32_byteswap_header
(elf);
+        if (grub_elf32_check_version
(elf) != GRUB_ERR_NONE)
+          return
grub_errno;
+        break;
+      case ELFCLASS64:
+        if (e->e_ident[EI_DATA]
!= ELFDATA_NATIVE)
+          grub_elf64_byteswap_header
(elf);
+        if (grub_elf64_check_version
(elf) != GRUB_ERR_NONE)
+          return
grub_errno;
+        break;
+      default:
+        return
grub_error (GRUB_ERR_BAD_OS, N_("unrecognized ELF class"));
+        break;
+    }
+  
   return GRUB_ERR_NONE;
 }
 
@@ -127,7 +152,16 @@ grub_elf_open (const
char *name)
 #define grub_elf_is_elfXX grub_elf_is_elf32
 #define grub_elfXX_load_phdrs
grub_elf32_load_phdrs
 #define ElfXX_Phdr Elf32_Phdr
+#define ElfXX_Ehdr Elf32_Ehdr
 #define grub_uintXX_t grub_uint32_t
+/* for phdr/ehdr byte swaps */
+#define byte_swap_halfXX grub_swap_bytes16
+#define byte_swap_wordXX grub_swap_bytes32
+#define byte_swap_addrXX grub_swap_bytes32
+#define byte_swap_offXX grub_swap_bytes32
+#define byte_swap_XwordXX byte_swap_wordXX
/* the 64-bit phdr uses Xwords and the 32-bit uses words */
+#define grub_elfXX_byteswap_header
grub_elf32_byteswap_header
+#define grub_elfXX_check_version grub_elf32_check_version
 
 #include "elfXX.c"
 
@@ -140,7 +174,15 @@ grub_elf_open (const
char *name)
 #undef grub_elf_is_elfXX
 #undef grub_elfXX_load_phdrs
 #undef ElfXX_Phdr
+#undef ElfXX_Ehdr
 #undef grub_uintXX_t
+#undef byte_swap_halfXX
+#undef byte_swap_wordXX
+#undef byte_swap_addrXX
+#undef byte_swap_offXX
+#undef byte_swap_XwordXX
+#undef grub_elfXX_byteswap_header
+#undef grub_elfXX_check_version
 
 

 /* 64-bit */
@@ -153,6 +195,16 @@ grub_elf_open (const
char *name)
 #define grub_elf_is_elfXX grub_elf_is_elf64
 #define grub_elfXX_load_phdrs
grub_elf64_load_phdrs
 #define ElfXX_Phdr Elf64_Phdr
+#define ElfXX_Ehdr Elf64_Ehdr
 #define grub_uintXX_t grub_uint64_t
+/* for phdr/ehdr byte swaps */
+#define byte_swap_halfXX grub_swap_bytes16
+#define byte_swap_wordXX grub_swap_bytes32
+#define byte_swap_addrXX grub_swap_bytes64
+#define byte_swap_offXX grub_swap_bytes64
+#define byte_swap_XwordXX grub_swap_bytes64
+#define grub_elfXX_byteswap_header
grub_elf64_byteswap_header
+#define grub_elfXX_check_version grub_elf64_check_version
 
 #include "elfXX.c"
+
diff --git a/grub-core/kern/elfXX.c
b/grub-core/kern/elfXX.c
index 2e45449..09062ce 100644
--- a/grub-core/kern/elfXX.c
+++ b/grub-core/kern/elfXX.c
@@ -154,3 +154,47 @@ grub_elfXX_load
(grub_elf_t elf, const char *filename,
 
   return grub_errno;
 }
+
+void 
+grub_elfXX_byteswap_header (grub_elf_t
elf)
+{
+  ElfXX_Ehdr *e = &(elf->ehdr.ehdrXX);
+  ElfXX_Phdr *phdr;  
+
+  e->e_type = byte_swap_halfXX
(e->e_type);
+  e->e_machine = byte_swap_halfXX
(e->e_machine);
+  e->e_version = byte_swap_wordXX
(e->e_version);
+  e->e_entry = byte_swap_addrXX
(e->e_entry);
+  e->e_phoff = byte_swap_offXX
(e->e_phoff);
+  e->e_shoff = byte_swap_offXX
(e->e_shoff);
+  e->e_flags = byte_swap_wordXX
(e->e_flags);
+  e->e_ehsize = byte_swap_halfXX
(e->e_ehsize);   
+  e->e_phentsize = byte_swap_halfXX
(e->e_phentsize);   
+  e->e_phnum = byte_swap_halfXX
(e->e_phnum);   
+  e->e_shentsize = byte_swap_halfXX
(e->e_shentsize);   
+  e->e_shnum = byte_swap_halfXX
(e->e_shnum);
+  e->e_shstrndx = byte_swap_halfXX
(e->e_shstrndx);
+
+  FOR_ELFXX_PHDRS (elf,phdr)
+    {
+      phdr->p_type
= byte_swap_wordXX (phdr->p_type);
+      phdr->p_flags
= byte_swap_wordXX (phdr->p_flags);
+      phdr->p_offset
= byte_swap_offXX (phdr->p_offset);
+      phdr->p_vaddr
= byte_swap_addrXX (phdr->p_vaddr);
+      phdr->p_paddr
= byte_swap_addrXX (phdr->p_paddr);
+      phdr->p_filesz
= byte_swap_XwordXX (phdr->p_filesz);
+      phdr->p_memsz
= byte_swap_XwordXX (phdr->p_memsz);
+      phdr->p_align
= byte_swap_XwordXX (phdr->p_align);
+    } 
+
+}
+
+grub_err_t
+grub_elfXX_check_version (grub_elf_t
elf)
+{
+  if (elf->ehdr.ehdrXX.e_version
!= EV_CURRENT)
+    return grub_error (GRUB_ERR_BAD_OS,
N_("invalid arch-independent ELF magic"));
+
+  return GRUB_ERR_NONE;
+}
+
diff --git a/include/grub/elf.h b/include/grub/elf.h
index 140d24d..d5adf3f 100644
--- a/include/grub/elf.h
+++ b/include/grub/elf.h
@@ -56,6 +56,13 @@ typedef grub_uint16_t
Elf64_Section;
 typedef Elf32_Half Elf32_Versym;
 typedef Elf64_Half Elf64_Versym;
 
+/* Define the native endianness */

+
+#ifdef GRUB_CPU_WORDS_BIGENDIAN
+#define ELFDATA_NATIVE    
    ELFDATA2MSB
+#else
+#define ELFDATA_NATIVE    
    ELFDATA2LSB
+#endif
 
 /* The ELF file header.  This
appears at the start of every ELF file.  */