| /* |
| * 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 "elf.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. |
| */ |
| |
| /* 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'. " |
| "%ld 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 Elf64_Phdr * |
| phdr_read(const struct buffer *in, Elf64_Ehdr *ehdr, struct xdr *xdr, int bit64) |
| { |
| struct buffer b; |
| Elf64_Phdr *phdr; |
| int i; |
| |
| /* 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 NULL; |
| |
| /* gather up all the phdrs. |
| * We do them all at once because there is more |
| * than one loop over all the phdrs. |
| */ |
| phdr = calloc(sizeof(*phdr), ehdr->e_phnum); |
| for (i = 0; i < ehdr->e_phnum; i++) |
| elf_phdr(&b, &phdr[i], ehdr->e_phentsize, xdr, bit64); |
| |
| return phdr; |
| } |
| |
| static Elf64_Shdr * |
| shdr_read(const struct buffer *in, Elf64_Ehdr *ehdr, struct xdr *xdr, int bit64) |
| { |
| struct buffer b; |
| Elf64_Shdr *shdr; |
| int i; |
| |
| /* 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 NULL; |
| |
| /* gather up all the shdrs. */ |
| shdr = calloc(sizeof(*shdr), ehdr->e_shnum); |
| for (i = 0; i < ehdr->e_shnum; i++) |
| elf_shdr(&b, &shdr[i], ehdr->e_shentsize, xdr, bit64); |
| |
| return shdr; |
| } |
| |
| /* 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 xdr *xdr = &xdr_le; |
| int bit64 = 0; |
| struct buffer input; |
| |
| buffer_clone(&input, pinput); |
| |
| if (!iself(buffer_get(pinput))) { |
| ERROR("The stage file is not in ELF format!\n"); |
| return -1; |
| } |
| |
| 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); |
| |
| // The tool may work in architecture-independent way. |
| if (arch != CBFS_ARCHITECTURE_UNKNOWN && |
| !((ehdr->e_machine == EM_ARM) && (arch == CBFS_ARCHITECTURE_ARMV7)) && |
| !((ehdr->e_machine == EM_386) && (arch == CBFS_ARCHITECTURE_X86))) { |
| ERROR("The stage file has the wrong architecture\n"); |
| return -1; |
| } |
| |
| *pphdr = phdr_read(pinput, ehdr, xdr, bit64); |
| if (*pphdr == NULL) |
| return -1; |
| |
| if (!pshdr) |
| return 0; |
| |
| *pshdr = shdr_read(pinput, ehdr, xdr, bit64); |
| if (*pshdr == NULL) |
| return -1; |
| |
| return 0; |
| } |