On Wednesday, March 2, 2016, Daniel Kiper 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 > > --- > 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