| /* |
| * elf header parsing. |
| * |
| * Copyright (C) 2013 Google, Inc. |
| * |
| * This program is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License as published by |
| * the Free Software Foundation; version 2 of the License. |
| * |
| * This program is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| * GNU General Public License for more details. |
| * |
| * You should have received a copy of the GNU General Public License |
| * along with this program; if not, write to the Free Software |
| * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA, 02110-1301 USA |
| */ |
| |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| |
| #include "elfparsing.h" |
| #include "common.h" |
| #include "cbfs.h" |
| |
| /* |
| * Short form: this is complicated, but we've tried making it simple |
| * and we keep hitting problems with our ELF parsing. |
| * |
| * The ELF parsing situation has always been a bit tricky. In fact, |
| * we (and most others) have been getting it wrong in small ways for |
| * years. Recently this has caused real trouble for the ARM V8 build. |
| * In this file we attempt to finally get it right for all variations |
| * of endian-ness and word size and target architectures and |
| * architectures we might get run on. Phew!. To do this we borrow a |
| * page from the FreeBSD NFS xdr model (see elf_ehdr and elf_phdr), |
| * the Plan 9 endianness functions (see xdr.c), and Go interfaces (see |
| * how we use buffer structs in this file). This ends up being a bit |
| * wordy at the lowest level, but greatly simplifies the elf parsing |
| * code and removes a common source of bugs, namely, forgetting to |
| * flip type endianness when referencing a struct member. |
| * |
| * ELF files can have four combinations of data layout: 32/64, and |
| * big/little endian. Further, to add to the fun, depending on the |
| * word size, the size of the ELF structs varies. The coreboot SELF |
| * format is simpler in theory: it's supposed to be always BE, and the |
| * various struct members allow room for growth: the entry point is |
| * always 64 bits, for example, so the size of a SELF struct is |
| * constant, regardless of target architecture word size. Hence, we |
| * need to do some transformation of the ELF files. |
| * |
| * A given architecture, realistically, only supports one of the four |
| * combinations at a time as the 'native' format. Hence, our code has |
| * been sprinkled with every variation of [nh]to[hn][sll] over the |
| * years. We've never quite gotten it all right, however, and a quick |
| * pass over this code revealed another bug. It's all worked because, |
| * until now, all the working platforms that had CBFS were 32 LE. Even then, |
| * however, bugs crept in: we recently realized that we're not |
| * transforming the entry point to big format when we store into the |
| * SELF image. |
| * |
| * The problem is essentially an XDR operation: |
| * we have something in a foreign format and need to transform it. |
| * It's most like XDR because: |
| * 1) the byte order can be wrong |
| * 2) the word size can be wrong |
| * 3) the size of elements in the stream depends on the value |
| * of other elements in the stream |
| * it's not like XDR because: |
| * 1) the byte order can be right |
| * 2) the word size can be right |
| * 3) the struct members are all on a natural alignment |
| * |
| * Hence, this new approach. To cover word size issues, we *always* |
| * transform the two structs we care about, the file header and |
| * program header, into a native struct in the 64 bit format: |
| * |
| * [32,little] -> [Elf64_Ehdr, Elf64_Phdr] |
| * [64,little] -> [Elf64_Ehdr, Elf64_Phdr] |
| * [32,big] -> [Elf64_Ehdr, Elf64_Phdr] |
| * [64,big] -> [Elf64_Ehdr, Elf64_Phdr] |
| * Then we just use those structs, and all the need for inline ntoh* goes away, |
| * as well as all the chances for error. |
| * This works because all the SELF structs have fields large enough for |
| * the largest ELF 64 struct members, and all the Elf64 struct members |
| * are at least large enough for all ELF 32 struct members. |
| * We end up with one function to do all our ELF parsing, and two functions |
| * to transform the headers. For the put case, we also have |
| * XDR functions, and hopefully we'll never again spend 5 years with the |
| * wrong endian-ness on an output value :-) |
| * This should work for all word sizes and endianness we hope to target. |
| * I *really* don't want to be here for 128 bit addresses. |
| * |
| * The parse functions are called with a pointer to an input buffer |
| * struct. One might ask: are there enough bytes in the input buffer? |
| * We know there need to be at *least* sizeof(Elf32_Ehdr) + |
| * sizeof(Elf32_Phdr) bytes. Realistically, there has to be some data |
| * too. If we start to worry, though we have not in the past, we |
| * might apply the simple test: the input buffer needs to be at least |
| * sizeof(Elf64_Ehdr) + sizeof(Elf64_Phdr) bytes because, even if it's |
| * ELF 32, there's got to be *some* data! This is not theoretically |
| * accurate but it is actually good enough in practice. It allows the |
| * header transformation code to ignore the possibility of underrun. |
| * |
| * We also must accomodate different ELF files, and hence formats, |
| * in the same cbfs invocation. We might load a 64-bit payload |
| * on a 32-bit machine; we might even have a mixed armv7/armv8 |
| * SOC or even a system with an x86/ARM! |
| * |
| * A possibly problematic (though unlikely to be so) assumption |
| * is that we expect the BIOS to remain in the lowest 32 bits |
| * of the physical address space. Since ARMV8 has standardized |
| * on that, and x86_64 also has, this seems a safe assumption. |
| * |
| * To repeat, ELF structs are different sizes because ELF struct |
| * members are different sizes, depending on values in the ELF file |
| * header. For this we use the functions defined in xdr.c, which |
| * consume bytes, convert the endianness, and advance the data pointer |
| * in the buffer struct. |
| */ |
| |
| |
| static int iself(const void *input) |
| { |
| const Elf32_Ehdr *ehdr = input; |
| return !memcmp(ehdr->e_ident, ELFMAG, 4); |
| } |
| |
| /* Get the ident array, so we can figure out |
| * endian-ness, word size, and in future other useful |
| * parameters |
| */ |
| static void |
| elf_eident(struct buffer *input, Elf64_Ehdr *ehdr) |
| { |
| bgets(input, ehdr->e_ident, sizeof(ehdr->e_ident)); |
| } |
| |
| |
| static int |
| check_size(const struct buffer *b, size_t offset, size_t size, const char *desc) |
| { |
| if (size == 0) |
| return 0; |
| |
| if (offset >= buffer_size(b) || (offset + size) > buffer_size(b)) { |
| ERROR("The file is not large enough for the '%s'. " |
| "%zu bytes @ offset %zu, input %zu bytes.\n", |
| desc, size, offset, buffer_size(b)); |
| return -1; |
| } |
| return 0; |
| } |
| |
| static void |
| elf_ehdr(struct buffer *input, Elf64_Ehdr *ehdr, struct xdr *xdr, int bit64) |
| { |
| ehdr->e_type = xdr->get16(input); |
| ehdr->e_machine = xdr->get16(input); |
| ehdr->e_version = xdr->get32(input); |
| if (bit64){ |
| ehdr->e_entry = xdr->get64(input); |
| ehdr->e_phoff = xdr->get64(input); |
| ehdr->e_shoff = xdr->get64(input); |
| } else { |
| ehdr->e_entry = xdr->get32(input); |
| ehdr->e_phoff = xdr->get32(input); |
| ehdr->e_shoff = xdr->get32(input); |
| } |
| ehdr->e_flags = xdr->get32(input); |
| ehdr->e_ehsize = xdr->get16(input); |
| ehdr->e_phentsize = xdr->get16(input); |
| ehdr->e_phnum = xdr->get16(input); |
| ehdr->e_shentsize = xdr->get16(input); |
| ehdr->e_shnum = xdr->get16(input); |
| ehdr->e_shstrndx = xdr->get16(input); |
| } |
| |
| static void |
| elf_phdr(struct buffer *pinput, Elf64_Phdr *phdr, |
| int entsize, struct xdr *xdr, int bit64) |
| { |
| /* |
| * The entsize need not be sizeof(*phdr). |
| * Hence, it is easier to keep a copy of the input, |
| * as the xdr functions may not advance the input |
| * pointer the full entsize; rather than get tricky |
| * we just advance it below. |
| */ |
| struct buffer input; |
| buffer_clone(&input, pinput); |
| if (bit64){ |
| phdr->p_type = xdr->get32(&input); |
| phdr->p_flags = xdr->get32(&input); |
| phdr->p_offset = xdr->get64(&input); |
| phdr->p_vaddr = xdr->get64(&input); |
| phdr->p_paddr = xdr->get64(&input); |
| phdr->p_filesz = xdr->get64(&input); |
| phdr->p_memsz = xdr->get64(&input); |
| phdr->p_align = xdr->get64(&input); |
| } else { |
| phdr->p_type = xdr->get32(&input); |
| phdr->p_offset = xdr->get32(&input); |
| phdr->p_vaddr = xdr->get32(&input); |
| phdr->p_paddr = xdr->get32(&input); |
| phdr->p_filesz = xdr->get32(&input); |
| phdr->p_memsz = xdr->get32(&input); |
| phdr->p_flags = xdr->get32(&input); |
| phdr->p_align = xdr->get32(&input); |
| } |
| buffer_seek(pinput, entsize); |
| } |
| |
| static void |
| elf_shdr(struct buffer *pinput, Elf64_Shdr *shdr, |
| int entsize, struct xdr *xdr, int bit64) |
| { |
| /* |
| * The entsize need not be sizeof(*shdr). |
| * Hence, it is easier to keep a copy of the input, |
| * as the xdr functions may not advance the input |
| * pointer the full entsize; rather than get tricky |
| * we just advance it below. |
| */ |
| struct buffer input = *pinput; |
| if (bit64){ |
| shdr->sh_name = xdr->get32(&input); |
| shdr->sh_type = xdr->get32(&input); |
| shdr->sh_flags = xdr->get64(&input); |
| shdr->sh_addr = xdr->get64(&input); |
| shdr->sh_offset = xdr->get64(&input); |
| shdr->sh_size= xdr->get64(&input); |
| shdr->sh_link = xdr->get32(&input); |
| shdr->sh_info = xdr->get32(&input); |
| shdr->sh_addralign = xdr->get64(&input); |
| shdr->sh_entsize = xdr->get64(&input); |
| } else { |
| shdr->sh_name = xdr->get32(&input); |
| shdr->sh_type = xdr->get32(&input); |
| shdr->sh_flags = xdr->get32(&input); |
| shdr->sh_addr = xdr->get32(&input); |
| shdr->sh_offset = xdr->get32(&input); |
| shdr->sh_size = xdr->get32(&input); |
| shdr->sh_link = xdr->get32(&input); |
| shdr->sh_info = xdr->get32(&input); |
| shdr->sh_addralign = xdr->get32(&input); |
| shdr->sh_entsize = xdr->get32(&input); |
| } |
| buffer_seek(pinput, entsize); |
| } |
| |
| static int |
| phdr_read(const struct buffer *in, struct parsed_elf *pelf, |
| struct xdr *xdr, int bit64) |
| { |
| struct buffer b; |
| Elf64_Phdr *phdr; |
| Elf64_Ehdr *ehdr; |
| int i; |
| |
| ehdr = &pelf->ehdr; |
| /* cons up an input buffer for the headers. |
| * Note that the program headers can be anywhere, |
| * per the ELF spec, You'd be surprised how many ELF |
| * readers miss this little detail. |
| */ |
| buffer_splice(&b, in, ehdr->e_phoff, ehdr->e_phentsize * ehdr->e_phnum); |
| if (check_size(in, ehdr->e_phoff, buffer_size(&b), "program headers")) |
| return -1; |
| |
| /* gather up all the phdrs. |
| * We do them all at once because there is more |
| * than one loop over all the phdrs. |
| */ |
| phdr = calloc(ehdr->e_phnum, sizeof(*phdr)); |
| for (i = 0; i < ehdr->e_phnum; i++) { |
| DEBUG("Parsing segment %d\n", i); |
| elf_phdr(&b, &phdr[i], ehdr->e_phentsize, xdr, bit64); |
| |
| /* Ensure the contents are valid within the elf file. */ |
| if (check_size(in, phdr[i].p_offset, phdr[i].p_filesz, |
| "segment contents")) { |
| free(phdr); |
| return -1; |
| } |
| } |
| |
| pelf->phdr = phdr; |
| |
| return 0; |
| } |
| |
| static int |
| shdr_read(const struct buffer *in, struct parsed_elf *pelf, |
| struct xdr *xdr, int bit64) |
| { |
| struct buffer b; |
| Elf64_Shdr *shdr; |
| Elf64_Ehdr *ehdr; |
| int i; |
| |
| ehdr = &pelf->ehdr; |
| |
| /* cons up an input buffer for the section headers. |
| * Note that the section headers can be anywhere, |
| * per the ELF spec, You'd be surprised how many ELF |
| * readers miss this little detail. |
| */ |
| buffer_splice(&b, in, ehdr->e_shoff, ehdr->e_shentsize * ehdr->e_shnum); |
| if (check_size(in, ehdr->e_shoff, buffer_size(&b), "section headers")) |
| return -1; |
| |
| /* gather up all the shdrs. */ |
| shdr = calloc(ehdr->e_shnum, sizeof(*shdr)); |
| for (i = 0; i < ehdr->e_shnum; i++) { |
| DEBUG("Parsing section %d\n", i); |
| elf_shdr(&b, &shdr[i], ehdr->e_shentsize, xdr, bit64); |
| } |
| |
| pelf->shdr = shdr; |
| |
| return 0; |
| } |
| |
| static int |
| reloc_read(const struct buffer *in, struct parsed_elf *pelf, |
| struct xdr *xdr, int bit64) |
| { |
| struct buffer b; |
| Elf64_Word i; |
| Elf64_Ehdr *ehdr; |
| |
| ehdr = &pelf->ehdr; |
| pelf->relocs = calloc(ehdr->e_shnum, sizeof(Elf64_Rela *)); |
| |
| /* Allocate array for each section that contains relocation entries. */ |
| for (i = 0; i < ehdr->e_shnum; i++) { |
| Elf64_Shdr *shdr; |
| Elf64_Rela *rela; |
| Elf64_Xword j; |
| Elf64_Xword nrelocs; |
| int is_rela; |
| |
| shdr = &pelf->shdr[i]; |
| |
| /* Only process REL and RELA sections. */ |
| if (shdr->sh_type != SHT_REL && shdr->sh_type != SHT_RELA) |
| continue; |
| |
| DEBUG("Checking relocation section %u\n", i); |
| |
| /* Ensure the section that relocations apply is a valid. */ |
| if (shdr->sh_info >= ehdr->e_shnum || |
| shdr->sh_info == SHN_UNDEF) { |
| ERROR("Relocations apply to an invalid section: %u\n", |
| shdr[i].sh_info); |
| return -1; |
| } |
| |
| is_rela = shdr->sh_type == SHT_RELA; |
| |
| /* Determine the number relocations in this section. */ |
| nrelocs = shdr->sh_size / shdr->sh_entsize; |
| |
| pelf->relocs[i] = calloc(nrelocs, sizeof(Elf64_Rela)); |
| |
| buffer_splice(&b, in, shdr->sh_offset, shdr->sh_size); |
| if (check_size(in, shdr->sh_offset, buffer_size(&b), |
| "relocation section")) { |
| ERROR("Relocation section %u failed.\n", i); |
| return -1; |
| } |
| |
| rela = pelf->relocs[i]; |
| for (j = 0; j < nrelocs; j++) { |
| if (bit64) { |
| rela->r_offset = xdr->get64(&b); |
| rela->r_info = xdr->get64(&b); |
| if (is_rela) |
| rela->r_addend = xdr->get64(&b); |
| } else { |
| uint32_t r_info; |
| |
| rela->r_offset = xdr->get32(&b); |
| r_info = xdr->get32(&b); |
| rela->r_info = ELF64_R_INFO(ELF32_R_SYM(r_info), |
| ELF32_R_TYPE(r_info)); |
| if (is_rela) |
| rela->r_addend = xdr->get32(&b); |
| } |
| rela++; |
| } |
| } |
| |
| return 0; |
| } |
| |
| static int strtab_read(const struct buffer *in, struct parsed_elf *pelf) |
| { |
| Elf64_Ehdr *ehdr; |
| Elf64_Word i; |
| |
| ehdr = &pelf->ehdr; |
| |
| if (ehdr->e_shstrndx >= ehdr->e_shnum) { |
| ERROR("Section header string table index out of range: %d\n", |
| ehdr->e_shstrndx); |
| return -1; |
| } |
| |
| /* For each section of type SHT_STRTAB create a symtab buffer. */ |
| pelf->strtabs = calloc(ehdr->e_shnum, sizeof(struct buffer *)); |
| |
| for (i = 0; i < ehdr->e_shnum; i++) { |
| struct buffer *b; |
| Elf64_Shdr *shdr = &pelf->shdr[i]; |
| |
| if (shdr->sh_type != SHT_STRTAB) |
| continue; |
| |
| b = calloc(1, sizeof(*b)); |
| buffer_splice(b, in, shdr->sh_offset, shdr->sh_size); |
| if (check_size(in, shdr->sh_offset, buffer_size(b), "strtab")) { |
| ERROR("STRTAB section not within bounds: %d\n", i); |
| free(b); |
| return -1; |
| } |
| pelf->strtabs[i] = b; |
| } |
| |
| return 0; |
| } |
| |
| static int |
| symtab_read(const struct buffer *in, struct parsed_elf *pelf, |
| struct xdr *xdr, int bit64) |
| { |
| Elf64_Ehdr *ehdr; |
| Elf64_Shdr *shdr; |
| Elf64_Half i; |
| Elf64_Xword nsyms; |
| Elf64_Sym *sym; |
| struct buffer b; |
| |
| ehdr = &pelf->ehdr; |
| |
| shdr = NULL; |
| for (i = 0; i < ehdr->e_shnum; i++) { |
| if (pelf->shdr[i].sh_type != SHT_SYMTAB) |
| continue; |
| |
| if (shdr != NULL) { |
| ERROR("Multiple symbol sections found. %u and %u\n", |
| (unsigned int)(shdr - pelf->shdr), i); |
| return -1; |
| } |
| |
| shdr = &pelf->shdr[i]; |
| } |
| |
| if (shdr == NULL) { |
| ERROR("No symbol table found.\n"); |
| return -1; |
| } |
| |
| buffer_splice(&b, in, shdr->sh_offset, shdr->sh_size); |
| if (check_size(in, shdr->sh_offset, buffer_size(&b), "symtab")) |
| return -1; |
| |
| nsyms = shdr->sh_size / shdr->sh_entsize; |
| |
| pelf->syms = calloc(nsyms, sizeof(Elf64_Sym)); |
| |
| for (i = 0; i < nsyms; i++) { |
| sym = &pelf->syms[i]; |
| |
| if (bit64) { |
| sym->st_name = xdr->get32(&b); |
| sym->st_info = xdr->get8(&b); |
| sym->st_other = xdr->get8(&b); |
| sym->st_shndx = xdr->get16(&b); |
| sym->st_value = xdr->get64(&b); |
| sym->st_size = xdr->get64(&b); |
| } else { |
| sym->st_name = xdr->get32(&b); |
| sym->st_value = xdr->get32(&b); |
| sym->st_size = xdr->get32(&b); |
| sym->st_info = xdr->get8(&b); |
| sym->st_other = xdr->get8(&b); |
| sym->st_shndx = xdr->get16(&b); |
| } |
| } |
| |
| return 0; |
| } |
| |
| int parse_elf(const struct buffer *pinput, struct parsed_elf *pelf, int flags) |
| { |
| struct xdr *xdr = &xdr_le; |
| int bit64 = 0; |
| struct buffer input; |
| Elf64_Ehdr *ehdr; |
| |
| /* Zero out the parsed elf structure. */ |
| memset(pelf, 0, sizeof(*pelf)); |
| |
| if (!iself(buffer_get(pinput))) { |
| ERROR("The stage file is not in ELF format!\n"); |
| return -1; |
| } |
| |
| buffer_clone(&input, pinput); |
| ehdr = &pelf->ehdr; |
| elf_eident(&input, ehdr); |
| bit64 = ehdr->e_ident[EI_CLASS] == ELFCLASS64; |
| /* Assume LE unless we are sure otherwise. |
| * We're not going to take on the task of |
| * fully validating the ELF file. That way |
| * lies madness. |
| */ |
| if (ehdr->e_ident[EI_DATA] == ELFDATA2MSB) |
| xdr = &xdr_be; |
| |
| elf_ehdr(&input, ehdr, xdr, bit64); |
| |
| /* Relocation processing requires section header parsing. */ |
| if (flags & ELF_PARSE_RELOC) |
| flags |= ELF_PARSE_SHDR; |
| |
| /* String table processing requires section header parsing. */ |
| if (flags & ELF_PARSE_STRTAB) |
| flags |= ELF_PARSE_SHDR; |
| |
| /* Symbole table processing requires section header parsing. */ |
| if (flags & ELF_PARSE_SYMTAB) |
| flags |= ELF_PARSE_SHDR; |
| |
| if ((flags & ELF_PARSE_PHDR) && phdr_read(pinput, pelf, xdr, bit64)) |
| goto fail; |
| |
| if ((flags & ELF_PARSE_SHDR) && shdr_read(pinput, pelf, xdr, bit64)) |
| goto fail; |
| |
| if ((flags & ELF_PARSE_RELOC) && reloc_read(pinput, pelf, xdr, bit64)) |
| goto fail; |
| |
| if ((flags & ELF_PARSE_STRTAB) && strtab_read(pinput, pelf)) |
| goto fail; |
| |
| if ((flags & ELF_PARSE_SYMTAB) && symtab_read(pinput, pelf, xdr, bit64)) |
| goto fail; |
| |
| return 0; |
| |
| fail: |
| parsed_elf_destroy(pelf); |
| return -1; |
| } |
| |
| void parsed_elf_destroy(struct parsed_elf *pelf) |
| { |
| Elf64_Half i; |
| |
| free(pelf->phdr); |
| free(pelf->shdr); |
| if (pelf->relocs != NULL) { |
| for (i = 0; i < pelf->ehdr.e_shnum; i++) |
| free(pelf->relocs[i]); |
| } |
| free(pelf->relocs); |
| |
| if (pelf->strtabs != NULL) { |
| for (i = 0; i < pelf->ehdr.e_shnum; i++) |
| free(pelf->strtabs[i]); |
| } |
| free(pelf->strtabs); |
| free(pelf->syms); |
| } |
| |
| /* Get the headers from the buffer. |
| * Return -1 in the event of an error. |
| * The section headers are optional; if NULL |
| * is passed in for pshdr they won't be parsed. |
| * We don't (yet) make payload parsing optional |
| * because we've never seen a use case. |
| */ |
| int |
| elf_headers(const struct buffer *pinput, |
| uint32_t arch, |
| Elf64_Ehdr *ehdr, |
| Elf64_Phdr **pphdr, |
| Elf64_Shdr **pshdr) |
| { |
| |
| struct parsed_elf pelf; |
| int flags; |
| |
| flags = ELF_PARSE_PHDR; |
| |
| if (pshdr != NULL) |
| flags |= ELF_PARSE_SHDR; |
| |
| if (parse_elf(pinput, &pelf, flags)) |
| return -1; |
| |
| /* Copy out the parsed elf header. */ |
| memcpy(ehdr, &pelf.ehdr, sizeof(*ehdr)); |
| |
| // The tool may work in architecture-independent way. |
| if (arch != CBFS_ARCHITECTURE_UNKNOWN && |
| !((ehdr->e_machine == EM_ARM) && (arch == CBFS_ARCHITECTURE_ARM)) && |
| !((ehdr->e_machine == EM_RISCV) && (arch == CBFS_ARCHITECTURE_RISCV)) && |
| !((ehdr->e_machine == EM_386) && (arch == CBFS_ARCHITECTURE_X86))) { |
| ERROR("The stage file has the wrong architecture\n"); |
| return -1; |
| } |
| |
| *pphdr = calloc(ehdr->e_phnum, sizeof(Elf64_Phdr)); |
| memcpy(*pphdr, pelf.phdr, ehdr->e_phnum * sizeof(Elf64_Phdr)); |
| |
| if (pshdr != NULL) { |
| *pshdr = calloc(ehdr->e_shnum, sizeof(Elf64_Shdr)); |
| memcpy(*pshdr, pelf.shdr, ehdr->e_shnum * sizeof(Elf64_Shdr)); |
| } |
| |
| parsed_elf_destroy(&pelf); |
| |
| return 0; |
| } |
| |
| /* ELF Writing Support |
| * |
| * The ELF file is written according to the following layout: |
| * +------------------+ |
| * | ELF Header | |
| * +------------------+ |
| * | Section Headers | |
| * +------------------+ |
| * | Program Headers | |
| * +------------------+ |
| * | String table | |
| * +------------------+ <- 4KiB Aligned |
| * | Code/Data | |
| * +------------------+ |
| */ |
| |
| /* Arbitray maximum number of sections. */ |
| #define MAX_SECTIONS 16 |
| struct elf_writer_section { |
| Elf64_Shdr shdr; |
| struct buffer content; |
| const char *name; |
| }; |
| |
| struct elf_writer |
| { |
| Elf64_Ehdr ehdr; |
| struct xdr *xdr; |
| size_t num_secs; |
| struct elf_writer_section sections[MAX_SECTIONS]; |
| Elf64_Phdr *phdrs; |
| struct elf_writer_section *shstrtab; |
| int bit64; |
| }; |
| |
| struct elf_writer *elf_writer_init(const Elf64_Ehdr *ehdr) |
| { |
| struct elf_writer *ew; |
| Elf64_Shdr shdr; |
| struct buffer empty_buffer; |
| |
| if (!iself(ehdr)) |
| return NULL; |
| |
| ew = calloc(1, sizeof(*ew)); |
| |
| memcpy(&ew->ehdr, ehdr, sizeof(ew->ehdr)); |
| |
| ew->bit64 = ew->ehdr.e_ident[EI_CLASS] == ELFCLASS64; |
| |
| /* Set the endinan ops. */ |
| if (ew->ehdr.e_ident[EI_DATA] == ELFDATA2MSB) |
| ew->xdr = &xdr_be; |
| else |
| ew->xdr = &xdr_le; |
| |
| /* Reset count and offsets */ |
| ew->ehdr.e_phoff = 0; |
| ew->ehdr.e_shoff = 0; |
| ew->ehdr.e_shnum = 0; |
| ew->ehdr.e_phnum = 0; |
| |
| memset(&empty_buffer, 0, sizeof(empty_buffer)); |
| memset(&shdr, 0, sizeof(shdr)); |
| |
| /* Add SHT_NULL section header. */ |
| shdr.sh_type = SHT_NULL; |
| elf_writer_add_section(ew, &shdr, &empty_buffer, NULL); |
| |
| /* Add section header string table and maintain reference to it. */ |
| shdr.sh_type = SHT_STRTAB; |
| elf_writer_add_section(ew, &shdr, &empty_buffer, ".shstrtab"); |
| ew->ehdr.e_shstrndx = ew->num_secs - 1; |
| ew->shstrtab = &ew->sections[ew->ehdr.e_shstrndx]; |
| |
| return ew; |
| } |
| |
| /* |
| * Clean up any internal state represented by ew. Aftewards the elf_writer |
| * is invalid. |
| */ |
| void elf_writer_destroy(struct elf_writer *ew) |
| { |
| if (ew->phdrs != NULL) |
| free(ew->phdrs); |
| free(ew); |
| } |
| |
| /* |
| * Add a section to the ELF file. Section type, flags, and memsize are |
| * maintained from the passed in Elf64_Shdr. The buffer represents the |
| * content of the section while the name is the name of section itself. |
| * Returns < 0 on error, 0 on success. |
| */ |
| int elf_writer_add_section(struct elf_writer *ew, const Elf64_Shdr *shdr, |
| struct buffer *contents, const char *name) |
| { |
| struct elf_writer_section *newsh; |
| |
| if (ew->num_secs == MAX_SECTIONS) |
| return -1; |
| |
| newsh = &ew->sections[ew->num_secs]; |
| ew->num_secs++; |
| |
| memcpy(&newsh->shdr, shdr, sizeof(newsh->shdr)); |
| newsh->shdr.sh_offset = 0; |
| |
| newsh->name = name; |
| if (contents != NULL) |
| buffer_clone(&newsh->content, contents); |
| |
| return 0; |
| } |
| |
| static void ehdr_write(struct elf_writer *ew, struct buffer *m) |
| { |
| int i; |
| |
| for (i = 0; i < EI_NIDENT; i++) |
| ew->xdr->put8(m, ew->ehdr.e_ident[i]); |
| ew->xdr->put16(m, ew->ehdr.e_type); |
| ew->xdr->put16(m, ew->ehdr.e_machine); |
| ew->xdr->put32(m, ew->ehdr.e_version); |
| if (ew->bit64) { |
| ew->xdr->put64(m, ew->ehdr.e_entry); |
| ew->xdr->put64(m, ew->ehdr.e_phoff); |
| ew->xdr->put64(m, ew->ehdr.e_shoff); |
| } else { |
| ew->xdr->put32(m, ew->ehdr.e_entry); |
| ew->xdr->put32(m, ew->ehdr.e_phoff); |
| ew->xdr->put32(m, ew->ehdr.e_shoff); |
| } |
| ew->xdr->put32(m, ew->ehdr.e_flags); |
| ew->xdr->put16(m, ew->ehdr.e_ehsize); |
| ew->xdr->put16(m, ew->ehdr.e_phentsize); |
| ew->xdr->put16(m, ew->ehdr.e_phnum); |
| ew->xdr->put16(m, ew->ehdr.e_shentsize); |
| ew->xdr->put16(m, ew->ehdr.e_shnum); |
| ew->xdr->put16(m, ew->ehdr.e_shstrndx); |
| } |
| |
| static void shdr_write(struct elf_writer *ew, size_t n, struct buffer *m) |
| { |
| struct xdr *xdr = ew->xdr; |
| int bit64 = ew->bit64; |
| struct elf_writer_section *sec = &ew->sections[n]; |
| Elf64_Shdr *shdr = &sec->shdr; |
| |
| xdr->put32(m, shdr->sh_name); |
| xdr->put32(m, shdr->sh_type); |
| if (bit64) { |
| xdr->put64(m, shdr->sh_flags); |
| xdr->put64(m, shdr->sh_addr); |
| xdr->put64(m, shdr->sh_offset); |
| xdr->put64(m, shdr->sh_size); |
| xdr->put32(m, shdr->sh_link); |
| xdr->put32(m, shdr->sh_info); |
| xdr->put64(m, shdr->sh_addralign); |
| xdr->put64(m, shdr->sh_entsize); |
| } else { |
| xdr->put32(m, shdr->sh_flags); |
| xdr->put32(m, shdr->sh_addr); |
| xdr->put32(m, shdr->sh_offset); |
| xdr->put32(m, shdr->sh_size); |
| xdr->put32(m, shdr->sh_link); |
| xdr->put32(m, shdr->sh_info); |
| xdr->put32(m, shdr->sh_addralign); |
| xdr->put32(m, shdr->sh_entsize); |
| } |
| } |
| |
| static void |
| phdr_write(struct elf_writer *ew, struct buffer *m, Elf64_Phdr *phdr) |
| { |
| if (ew->bit64) { |
| ew->xdr->put32(m, phdr->p_type); |
| ew->xdr->put32(m, phdr->p_flags); |
| ew->xdr->put64(m, phdr->p_offset); |
| ew->xdr->put64(m, phdr->p_vaddr); |
| ew->xdr->put64(m, phdr->p_paddr); |
| ew->xdr->put64(m, phdr->p_filesz); |
| ew->xdr->put64(m, phdr->p_memsz); |
| ew->xdr->put64(m, phdr->p_align); |
| } else { |
| ew->xdr->put32(m, phdr->p_type); |
| ew->xdr->put32(m, phdr->p_offset); |
| ew->xdr->put32(m, phdr->p_vaddr); |
| ew->xdr->put32(m, phdr->p_paddr); |
| ew->xdr->put32(m, phdr->p_filesz); |
| ew->xdr->put32(m, phdr->p_memsz); |
| ew->xdr->put32(m, phdr->p_flags); |
| ew->xdr->put32(m, phdr->p_align); |
| } |
| |
| } |
| |
| /* |
| * Serialize the ELF file to the output buffer. Return < 0 on error, |
| * 0 on success. |
| */ |
| int elf_writer_serialize(struct elf_writer *ew, struct buffer *out) |
| { |
| Elf64_Half i; |
| Elf64_Xword metadata_size; |
| Elf64_Xword program_size; |
| Elf64_Off shstroffset; |
| size_t shstrlen; |
| struct buffer metadata; |
| struct buffer phdrs; |
| struct buffer data; |
| struct buffer *strtab; |
| |
| INFO("Writing %zu sections.\n", ew->num_secs); |
| |
| /* Determine size of sections to be written. */ |
| program_size = 0; |
| /* Start with 1 byte for first byte of section header string table. */ |
| shstrlen = 1; |
| for (i = 0; i < ew->num_secs; i++) { |
| struct elf_writer_section *sec = &ew->sections[i]; |
| |
| if (sec->shdr.sh_flags & SHF_ALLOC) |
| ew->ehdr.e_phnum++; |
| |
| program_size += buffer_size(&sec->content); |
| |
| /* Keep track of the length sections' names. */ |
| if (sec->name != NULL) { |
| sec->shdr.sh_name = shstrlen; |
| shstrlen += strlen(sec->name) + 1; |
| } |
| } |
| ew->ehdr.e_shnum = ew->num_secs; |
| metadata_size = 0; |
| metadata_size += ew->ehdr.e_ehsize; |
| metadata_size += ew->ehdr.e_shnum * ew->ehdr.e_shentsize; |
| metadata_size += ew->ehdr.e_phnum * ew->ehdr.e_phentsize; |
| shstroffset = metadata_size; |
| /* Align up section header string size and metadata size to 4KiB */ |
| metadata_size = ALIGN(metadata_size + shstrlen, 4096); |
| |
| if (buffer_create(out, metadata_size + program_size, "elfout")) { |
| ERROR("Could not create output buffer for ELF.\n"); |
| return -1; |
| } |
| |
| INFO("Created %zu output buffer for ELF file.\n", buffer_size(out)); |
| |
| /* |
| * Write out ELF header. Section headers come right after ELF header |
| * followed by the program headers. Buffers need to be created first |
| * to do the writing. |
| */ |
| ew->ehdr.e_shoff = ew->ehdr.e_ehsize; |
| ew->ehdr.e_phoff = ew->ehdr.e_shoff + |
| ew->ehdr.e_shnum * ew->ehdr.e_shentsize; |
| |
| buffer_splice(&metadata, out, 0, metadata_size); |
| buffer_splice(&phdrs, out, ew->ehdr.e_phoff, |
| ew->ehdr.e_phnum * ew->ehdr.e_phentsize); |
| buffer_splice(&data, out, metadata_size, program_size); |
| /* Set up the section header string table contents. */ |
| strtab = &ew->shstrtab->content; |
| buffer_splice(strtab, out, shstroffset, shstrlen); |
| ew->shstrtab->shdr.sh_size = shstrlen; |
| |
| /* Reset current locations. */ |
| buffer_set_size(&metadata, 0); |
| buffer_set_size(&data, 0); |
| buffer_set_size(&phdrs, 0); |
| buffer_set_size(strtab, 0); |
| |
| /* ELF Header */ |
| ehdr_write(ew, &metadata); |
| |
| /* Write out section headers, section strings, section content, and |
| * program headers. */ |
| ew->xdr->put8(strtab, 0); |
| for (i = 0; i < ew->num_secs; i++) { |
| Elf64_Phdr phdr; |
| struct elf_writer_section *sec = &ew->sections[i]; |
| |
| /* Update section offsets. Be sure to not update SHT_NULL. */ |
| if (sec == ew->shstrtab) |
| sec->shdr.sh_offset = shstroffset; |
| else if (i != 0) |
| sec->shdr.sh_offset = buffer_size(&data) + |
| metadata_size; |
| shdr_write(ew, i, &metadata); |
| |
| /* Add section name to string table. */ |
| if (sec->name != NULL) |
| bputs(strtab, sec->name, strlen(sec->name) + 1); |
| |
| if (!(sec->shdr.sh_flags & SHF_ALLOC)) |
| continue; |
| |
| bputs(&data, buffer_get(&sec->content), |
| buffer_size(&sec->content)); |
| |
| phdr.p_type = PT_LOAD; |
| phdr.p_offset = sec->shdr.sh_offset; |
| phdr.p_vaddr = sec->shdr.sh_addr; |
| phdr.p_paddr = sec->shdr.sh_addr; |
| phdr.p_filesz = buffer_size(&sec->content); |
| phdr.p_memsz = sec->shdr.sh_size; |
| phdr.p_flags = 0; |
| if (sec->shdr.sh_flags & SHF_EXECINSTR) |
| phdr.p_flags |= PF_X | PF_R; |
| if (sec->shdr.sh_flags & SHF_WRITE) |
| phdr.p_flags |= PF_W; |
| phdr.p_align = sec->shdr.sh_addralign; |
| phdr_write(ew, &phdrs, &phdr); |
| } |
| |
| return 0; |
| } |