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

[Andrey Borzenkov]

В Fri, 10 Jan 2014 11:58:58 -0600
Tomohiro B Berry <address@hidden> пишет:

> 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. 
> 

I wonder - when big endian grub will pass boot parameters to little
endian kernel - won't there be endianness mismatch?

> 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.  */