Re: [GRUB2 PATCH v3 4/4] multiboot2: Add support for relocatable images

["Vladimir 'phcoder' Serbinenko" <phcoder@gmail.com>]

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On Wednesday, March 2, 2016, Daniel Kiper <daniel.kiper@oracle.com> wrote:

> Currently multiboot2 protocol loads image exactly at address specified in
> ELF or multiboot2 header. This solution works quite well on legacy BIOS
> platforms. It is possible because memory regions are placed at predictable
> addresses (though I was not able to find any spec which says that it is
> strong requirement, so, it looks that it is just a goodwill of hardware
> designers). However, EFI platforms are more volatile. Even if required
> memory regions live at specific addresses then they are sometimes simply
> not free (e.g. used by boot/runtime services on Dell PowerEdge R820 and
> OVMF). This means that you are not able to simply set up final image
> destination on build time. You have to provide method to relocate image
> contents to real load address which is usually different than load address
> specified in ELF and multiboot2 headers.
>
> This patch provides all needed machinery to do self relocation in image
> code.
> First of all GRUB2 reads min_addr (min. load addr), max_addr (max. load
> addr),
> align (required image alignment), preference (it says which memory regions
> are
> preferred by image, e.g. none, low, high) from
> multiboot_header_tag_relocatable
> header tag contained in binary. Later loader tries to fulfill request (not
> only
> that one) and if it succeeds then it informs image about real load address
> via
> multiboot_tag_base_addr tag. At this stage GRUB2 role is finished. Starting
> from now executable must cope with relocations itself using whole static
> and dynamic knowledge provided by boot loader.
>
> This patch does not provide functionality which could do relocations using
> ELF relocation data.

Can you add a check that image doesn't have any relocation entries? So that
we fail nicely rather than loading half-working binary?

> However, I was asked by Konrad Rzeszutek Wilk and Vladimir
> 'phcoder' Serbinenko to investigate that thing. It looks that relevant
> machinery
> could be added to existing code (including this patch) without huge effort.
> Additionally, ELF relocation could live in parallel with self relocation
> provided
> by this patch. However, during research I realized that first of all we
> should
> establish the details how ELF relocatable image should look like and how
> it should
> be build. At least to build proper test/example files.
>
> As I saw multiboot2 protocol is able to consume ET_EXEC and ET_DYN ELF
> files.
> Potentially we can use ET_DYN file type. It can be build with gcc/ld -pie
> option.
> However, it contains a lot of unneeded stuff (e.g. INTERP, DYNAMIC,
> GNU_EH_FRAME
> program headers) and it could be quite difficult to drop them (Hmmm... Is
> it
> possible to build it properly with custom ld script?). So, I have checked
> ET_EXEC
> file type. Sadly in this case linker by default resolves all local symbol
> relocations
> and removes relocation related sections. Fortunately it is possible to
> leave them
> as is with simple -q/--emit-relocs ld option. However, output file is
> quite fragile
> and any operation on it should be done with great care (e.g. strip should
> be called
> with --strip-unneeded option). So, this solution is not perfect too. It
> means that
> maybe we should look for better solution. However, I think that we should
> not use
> any custom tools and focus on functionalities provided by compiler and
> binutils.
> In this context ld scripts looks quite promising but maybe you have better
> solutions.
> So, what do you think about that?
>
> This patch was tested with Xen image which uses that functionality.
> However, this Xen
> feature is still under development and new patchset will be released in
> about 3-4 weeks.
>
> Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com <javascript:;>>
> ---
> v3 - suggestions/fixes:
>    - reduce number of casts
>      (suggested by Konrad Rzeszutek Wilk),
>    - remove unneeded space at the end of line
>      (suggested by Konrad Rzeszutek Wilk),
>    - improve commit message
>      (suggested by Konrad Rzeszutek Wilk).
> ---
>  grub-core/loader/i386/multiboot_mbi.c |    6 ++-
>  grub-core/loader/multiboot.c          |   12 ++++--
>  grub-core/loader/multiboot_elfxx.c    |   28 ++++++++++----
>  grub-core/loader/multiboot_mbi2.c     |   65
> ++++++++++++++++++++++++++++++---
>  include/grub/multiboot.h              |    4 +-
>  include/multiboot2.h                  |   24 ++++++++++++
>  6 files changed, 120 insertions(+), 19 deletions(-)
>
> diff --git a/grub-core/loader/i386/multiboot_mbi.c
> b/grub-core/loader/i386/multiboot_mbi.c
> index f60b702..4fc83ed 100644
> --- a/grub-core/loader/i386/multiboot_mbi.c
> +++ b/grub-core/loader/i386/multiboot_mbi.c
> @@ -72,7 +72,8 @@ load_kernel (grub_file_t file, const char *filename,
>    grub_err_t err;
>    if (grub_multiboot_quirks & GRUB_MULTIBOOT_QUIRK_BAD_KLUDGE)
>      {
> -      err = grub_multiboot_load_elf (file, filename, buffer);
> +      err = grub_multiboot_load_elf (file, filename, buffer, 0, 0, 0, 0,
> +                                    GRUB_RELOCATOR_PREFERENCE_NONE, NULL,
> 0);
>        if (err == GRUB_ERR_NONE) {
>         return GRUB_ERR_NONE;
>        }
> @@ -121,7 +122,8 @@ load_kernel (grub_file_t file, const char *filename,
>        return GRUB_ERR_NONE;
>      }
>
> -  return grub_multiboot_load_elf (file, filename, buffer);
> +  return grub_multiboot_load_elf (file, filename, buffer, 0, 0, 0, 0,
> +                                 GRUB_RELOCATOR_PREFERENCE_NONE, NULL, 0);
>  }
>
>  static struct multiboot_header *
> diff --git a/grub-core/loader/multiboot.c b/grub-core/loader/multiboot.c
> index 18038fd..c0f51b6 100644
> --- a/grub-core/loader/multiboot.c
> +++ b/grub-core/loader/multiboot.c
> @@ -208,12 +208,18 @@ static grub_uint64_t highest_load;
>  /* Load ELF32 or ELF64.  */
>  grub_err_t
>  grub_multiboot_load_elf (grub_file_t file, const char *filename,
> -                        void *buffer)
> +                        void *buffer, int relocatable, grub_uint32_t
> min_addr,
> +                        grub_uint32_t max_addr, grub_size_t align,
> grub_uint32_t preference,
> +                        grub_uint32_t *base_addr, int
> avoid_efi_boot_services)
>  {
>    if (grub_multiboot_is_elf32 (buffer))
> -    return grub_multiboot_load_elf32 (file, filename, buffer);
> +    return grub_multiboot_load_elf32 (file, filename, buffer, relocatable,
> +                                     min_addr, max_addr, align,
> preference,
> +                                     base_addr, avoid_efi_boot_services);
>    else if (grub_multiboot_is_elf64 (buffer))
> -    return grub_multiboot_load_elf64 (file, filename, buffer);
> +    return grub_multiboot_load_elf64 (file, filename, buffer, relocatable,
> +                                     min_addr, max_addr, align,
> preference,
> +                                     base_addr, avoid_efi_boot_services);
>
>    return grub_error (GRUB_ERR_UNKNOWN_OS, N_("invalid arch-dependent ELF
> magic"));
>  }
> diff --git a/grub-core/loader/multiboot_elfxx.c
> b/grub-core/loader/multiboot_elfxx.c
> index e3a39b6..0c01569 100644
> --- a/grub-core/loader/multiboot_elfxx.c
> +++ b/grub-core/loader/multiboot_elfxx.c
> @@ -51,7 +51,10 @@ CONCAT(grub_multiboot_is_elf, XX) (void *buffer)
>  }
>
>  static grub_err_t
> -CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char
> *filename, void *buffer)
> +CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char
> *filename,
> +                                    void *buffer, int relocatable,
> grub_uint32_t min_addr,
> +                                    grub_uint32_t max_addr, grub_size_t
> align, grub_uint32_t preference,
> +                                    grub_uint32_t *base_addr, int
> avoid_efi_boot_services)
>  {
>    Elf_Ehdr *ehdr = (Elf_Ehdr *) buffer;
>    char *phdr_base;
> @@ -89,19 +92,30 @@ CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file,
> const char *filename, voi
>           if (phdr(i)->p_paddr + phdr(i)->p_memsz > highest_load)
>             highest_load = phdr(i)->p_paddr + phdr(i)->p_memsz;
>
> -         grub_dprintf ("multiboot_loader", "segment %d: paddr=0x%lx,
> memsz=0x%lx, vaddr=0x%lx\n",
> -                       i, (long) phdr(i)->p_paddr, (long)
> phdr(i)->p_memsz, (long) phdr(i)->p_vaddr);
> +         grub_dprintf ("multiboot_loader", "segment %d: paddr=0x%lx,
> memsz=0x%lx, vaddr=0x%lx,"
> +                       "align=0x%lx, relocatable=%d,
> avoid_efi_boot_services=%d\n", i,
> +                       (long) phdr(i)->p_paddr, (long) phdr(i)->p_memsz,
> (long) phdr(i)->p_vaddr,
> +                       (long) align, relocatable,
> avoid_efi_boot_services);
>
>           {
>             grub_relocator_chunk_t ch;
> -           err = grub_relocator_alloc_chunk_addr
> (grub_multiboot_relocator,
> -                                                  &ch, phdr(i)->p_paddr,
> -                                                  phdr(i)->p_memsz);
> +
> +           if (relocatable)
> +             err = grub_relocator_alloc_chunk_align
> (grub_multiboot_relocator, &ch,
> +                                                     min_addr, max_addr -
> phdr(i)->p_memsz,
> +                                                     phdr(i)->p_memsz,
> align ? align : 1,
> +                                                     preference,
> avoid_efi_boot_services);
> +           else
> +             err = grub_relocator_alloc_chunk_addr
> (grub_multiboot_relocator,
> +                                                    &ch, phdr(i)->p_paddr,
> +                                                    phdr(i)->p_memsz);
>             if (err)
>               {
>                 grub_dprintf ("multiboot_loader", "Error loading phdr
> %d\n", i);
>                 return err;
>               }
> +           if (base_addr)
> +             *base_addr = get_physical_target_address (ch);
>             source = get_virtual_current_address (ch);
>           }
>
> @@ -208,7 +222,7 @@ CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file,
> const char *filename, voi
>                                                     + 1, sh->sh_size,
>                                                     sh->sh_addralign,
>
> GRUB_RELOCATOR_PREFERENCE_NONE,
> -                                                   0);
> +
>  avoid_efi_boot_services);
>             if (err)
>               {
>                 grub_dprintf ("multiboot_loader", "Error loading shdr
> %d\n", i);
> diff --git a/grub-core/loader/multiboot_mbi2.c
> b/grub-core/loader/multiboot_mbi2.c
> index ce68f48..03725a1 100644
> --- a/grub-core/loader/multiboot_mbi2.c
> +++ b/grub-core/loader/multiboot_mbi2.c
> @@ -68,6 +68,7 @@ static grub_size_t elf_sec_num, elf_sec_entsize;
>  static unsigned elf_sec_shstrndx;
>  static void *elf_sections;
>  static int keep_bs = 0;
> +static grub_uint32_t base_addr = 0;
>
>  void
>  grub_multiboot_add_elfsyms (grub_size_t num, grub_size_t entsize,
> @@ -107,11 +108,14 @@ grub_multiboot_load (grub_file_t file, const char
> *filename)
>    grub_err_t err;
>    struct multiboot_header_tag *tag;
>    struct multiboot_header_tag_address *addr_tag = NULL;
> -  int entry_specified = 0, efi_entry_specified = 0;
> +  struct multiboot_header_tag_relocatable *rel_tag;
> +  int entry_specified = 0, efi_entry_specified = 0, relocatable = 0;
>    grub_addr_t entry = 0, efi_entry = 0;
> -  grub_uint32_t console_required = 0;
> +  grub_uint32_t console_required = 0, min_addr = 0;
> +  grub_uint32_t max_addr = 0, preference = GRUB_RELOCATOR_PREFERENCE_NONE;
>    struct multiboot_header_tag_framebuffer *fbtag = NULL;
>    int accepted_consoles = GRUB_MULTIBOOT_CONSOLE_EGA_TEXT;
> +  grub_size_t align = 0;
>
>    buffer = grub_malloc (MULTIBOOT_SEARCH);
>    if (!buffer)
> @@ -174,6 +178,7 @@ grub_multiboot_load (grub_file_t file, const char
> *filename)
>               case MULTIBOOT_TAG_TYPE_EFI_BS:
>               case MULTIBOOT_TAG_TYPE_EFI32_IH:
>               case MULTIBOOT_TAG_TYPE_EFI64_IH:
> +             case MULTIBOOT_TAG_TYPE_BASE_ADDR:
>                 break;
>
>               default:
> @@ -215,6 +220,27 @@ grub_multiboot_load (grub_file_t file, const char
> *filename)
>         accepted_consoles |= GRUB_MULTIBOOT_CONSOLE_FRAMEBUFFER;
>         break;
>
> +      case MULTIBOOT_HEADER_TAG_RELOCATABLE:
> +       relocatable = 1;
> +       rel_tag = (struct multiboot_header_tag_relocatable *) tag;
> +       min_addr = rel_tag->min_addr;
> +       max_addr = rel_tag->max_addr;
> +       align = rel_tag->align;
> +       switch (rel_tag->preference)
> +         {
> +         case MULTIBOOT_LOAD_PREFERENCE_LOW:
> +           preference = GRUB_RELOCATOR_PREFERENCE_LOW;
> +           break;
> +
> +         case MULTIBOOT_LOAD_PREFERENCE_HIGH:
> +           preference = GRUB_RELOCATOR_PREFERENCE_HIGH;
> +           break;
> +
> +         default:
> +           preference = GRUB_RELOCATOR_PREFERENCE_NONE;
> +         }
> +       break;
> +
>         /* GRUB always page-aligns modules.  */
>        case MULTIBOOT_HEADER_TAG_MODULE_ALIGN:
>         break;
> @@ -260,15 +286,22 @@ grub_multiboot_load (grub_file_t file, const char
> *filename)
>        else
>         code_size = load_size;
>
> -      err = grub_relocator_alloc_chunk_addr (grub_multiboot_relocator,
> -                                            &ch, load_addr,
> -                                            code_size);
> +      if (relocatable)
> +       err = grub_relocator_alloc_chunk_align (grub_multiboot_relocator,
> &ch,
> +                                               min_addr, max_addr -
> code_size,
> +                                               code_size, align ? align :
> 1,
> +                                               preference, keep_bs);
> +      else
> +       err = grub_relocator_alloc_chunk_addr (grub_multiboot_relocator,
> +                                              &ch, load_addr,
> +                                              code_size);
>        if (err)
>         {
>           grub_dprintf ("multiboot_loader", "Error loading aout kludge\n");
>           grub_free (buffer);
>           return err;
>         }
> +      base_addr = get_physical_target_address (ch);
>        source = get_virtual_current_address (ch);
>
>        if ((grub_file_seek (file, offset)) == (grub_off_t) -1)
> @@ -290,7 +323,9 @@ grub_multiboot_load (grub_file_t file, const char
> *filename)
>      }
>    else
>      {
> -      err = grub_multiboot_load_elf (file, filename, buffer);
> +      err = grub_multiboot_load_elf (file, filename, buffer,
> +                                    relocatable, min_addr, max_addr,
> +                                    align, preference, &base_addr,
> keep_bs);
>        if (err)
>         {
>           grub_free (buffer);
> @@ -303,6 +338,14 @@ grub_multiboot_load (grub_file_t file, const char
> *filename)
>    else if (entry_specified)
>      grub_multiboot_payload_eip = entry;
>
> +  if (relocatable)
> +    {
> +      if (base_addr > min_addr)
> +       grub_multiboot_payload_eip += base_addr - min_addr;
> +      else
> +       grub_multiboot_payload_eip -= min_addr - base_addr;
> +    }
> +
>    if (fbtag)
>      err = grub_multiboot_set_console (GRUB_MULTIBOOT_CONSOLE_FRAMEBUFFER,
>                                       accepted_consoles,
> @@ -409,6 +452,7 @@ grub_multiboot_get_mbi_size (void)
>                  + grub_get_multiboot_mmap_count ()
>                  * sizeof (struct multiboot_mmap_entry)),
> MULTIBOOT_TAG_ALIGN)
>      + ALIGN_UP (sizeof (struct multiboot_tag_framebuffer),
> MULTIBOOT_TAG_ALIGN)
> +    + ALIGN_UP (sizeof (struct multiboot_tag_base_addr),
> MULTIBOOT_TAG_ALIGN)
>  #ifdef GRUB_MACHINE_EFI
>  #ifdef __i386__
>      + ALIGN_UP (sizeof (struct multiboot_tag_efi32), MULTIBOOT_TAG_ALIGN)
> @@ -698,6 +742,15 @@ grub_multiboot_make_mbi (grub_uint32_t *target)
>    ptrorig += (2 * sizeof (grub_uint32_t)) / sizeof
> (grub_properly_aligned_t);
>
>    {
> +    struct multiboot_tag_base_addr *tag = (struct multiboot_tag_base_addr
> *) ptrorig;
> +    tag->type = MULTIBOOT_TAG_TYPE_BASE_ADDR;
> +    tag->size = sizeof (struct multiboot_tag_base_addr);
> +    tag->base_addr = base_addr;
> +    ptrorig += ALIGN_UP (tag->size, MULTIBOOT_TAG_ALIGN)
> +       / sizeof (grub_properly_aligned_t);
> +  }
> +
> +  {
>      struct multiboot_tag_string *tag = (struct multiboot_tag_string *)
> ptrorig;
>      tag->type = MULTIBOOT_TAG_TYPE_CMDLINE;
>      tag->size = sizeof (struct multiboot_tag_string) + cmdline_size;
> diff --git a/include/grub/multiboot.h b/include/grub/multiboot.h
> index e13c084..ec322b0 100644
> --- a/include/grub/multiboot.h
> +++ b/include/grub/multiboot.h
> @@ -94,7 +94,9 @@ grub_multiboot_load (grub_file_t file, const char
> *filename);
>  /* Load ELF32 or ELF64.  */
>  grub_err_t
>  grub_multiboot_load_elf (grub_file_t file, const char *filename,
> -                        void *buffer);
> +                        void *buffer, int relocatable, grub_uint32_t
> min_addr,
> +                        grub_uint32_t max_addr, grub_size_t align,
> grub_uint32_t preference,
> +                        grub_uint32_t *base_addr, int
> avoid_efi_boot_services);
>  extern grub_size_t grub_multiboot_pure_size;
>  extern grub_size_t grub_multiboot_alloc_mbi;
>  extern grub_uint32_t grub_multiboot_payload_eip;
> diff --git a/include/multiboot2.h b/include/multiboot2.h
> index 36a174f..c09bdbc 100644
> --- a/include/multiboot2.h
> +++ b/include/multiboot2.h
> @@ -62,6 +62,7 @@
>  #define MULTIBOOT_TAG_TYPE_EFI_BS            18
>  #define MULTIBOOT_TAG_TYPE_EFI32_IH          19
>  #define MULTIBOOT_TAG_TYPE_EFI64_IH          20
> +#define MULTIBOOT_TAG_TYPE_BASE_ADDR         21
>
>  #define MULTIBOOT_HEADER_TAG_END  0
>  #define MULTIBOOT_HEADER_TAG_INFORMATION_REQUEST  1
> @@ -72,11 +73,16 @@
>  #define MULTIBOOT_HEADER_TAG_MODULE_ALIGN  6
>  #define MULTIBOOT_HEADER_TAG_EFI_BS  7
>  #define MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS_EFI64  9
> +#define MULTIBOOT_HEADER_TAG_RELOCATABLE  10
>
>  #define MULTIBOOT_ARCHITECTURE_I386  0
>  #define MULTIBOOT_ARCHITECTURE_MIPS32  4
>  #define MULTIBOOT_HEADER_TAG_OPTIONAL 1
>
> +#define MULTIBOOT_LOAD_PREFERENCE_NONE 0
> +#define MULTIBOOT_LOAD_PREFERENCE_LOW 1
> +#define MULTIBOOT_LOAD_PREFERENCE_HIGH 2
> +
>  #define MULTIBOOT_CONSOLE_FLAGS_CONSOLE_REQUIRED 1
>  #define MULTIBOOT_CONSOLE_FLAGS_EGA_TEXT_SUPPORTED 2
>
> @@ -161,6 +167,17 @@ struct multiboot_header_tag_module_align
>    multiboot_uint32_t size;
>  };
>
> +struct multiboot_header_tag_relocatable
> +{
> +  multiboot_uint16_t type;
> +  multiboot_uint16_t flags;
> +  multiboot_uint32_t size;
> +  multiboot_uint32_t min_addr;
> +  multiboot_uint32_t max_addr;
> +  multiboot_uint32_t align;
> +  multiboot_uint32_t preference;
> +};
> +
>  struct multiboot_color
>  {
>    multiboot_uint8_t red;
> @@ -387,6 +404,13 @@ struct multiboot_tag_efi64_ih
>    multiboot_uint64_t pointer;
>  };
>
> +struct multiboot_tag_base_addr
> +{
> +  multiboot_uint32_t type;
> +  multiboot_uint32_t size;
> +  multiboot_uint32_t base_addr;
> +};
> +
>  #endif /* ! ASM_FILE */
>
>  #endif /* ! MULTIBOOT_HEADER */
> --
> 1.7.10.4
>
>

-- 
Regards
Vladimir 'phcoder' Serbinenko

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