coreboot-kgpe-d16/util/cbfstool/elfheaders.c

1442 lines
38 KiB
C

/*
* 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.
*/
#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))) {
DEBUG("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,
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));
*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 |
* +------------------+
*/
void elf_init_eheader(Elf64_Ehdr *ehdr, int machine, int nbits, int endian)
{
memset(ehdr, 0, sizeof(*ehdr));
ehdr->e_ident[EI_MAG0] = ELFMAG0;
ehdr->e_ident[EI_MAG1] = ELFMAG1;
ehdr->e_ident[EI_MAG2] = ELFMAG2;
ehdr->e_ident[EI_MAG3] = ELFMAG3;
ehdr->e_ident[EI_CLASS] = nbits;
ehdr->e_ident[EI_DATA] = endian;
ehdr->e_ident[EI_VERSION] = EV_CURRENT;
ehdr->e_type = ET_EXEC;
ehdr->e_machine = machine;
ehdr->e_version = EV_CURRENT;
if (nbits == ELFCLASS64) {
ehdr->e_ehsize = sizeof(Elf64_Ehdr);
ehdr->e_phentsize = sizeof(Elf64_Phdr);
ehdr->e_shentsize = sizeof(Elf64_Shdr);
} else {
ehdr->e_ehsize = sizeof(Elf32_Ehdr);
ehdr->e_phentsize = sizeof(Elf32_Phdr);
ehdr->e_shentsize = sizeof(Elf32_Shdr);
}
}
/* 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_string_table {
size_t next_offset;
size_t max_size;
char *buffer;
};
struct elf_writer_sym_table {
size_t max_entries;
size_t num_entries;
Elf64_Sym *syms;
};
#define MAX_REL_NAME 32
struct elf_writer_rel {
size_t num_entries;
size_t max_entries;
Elf64_Rel *rels;
struct elf_writer_section *sec;
char name[MAX_REL_NAME];
};
struct elf_writer
{
Elf64_Ehdr ehdr;
struct xdr *xdr;
size_t num_secs;
struct elf_writer_section sections[MAX_SECTIONS];
struct elf_writer_rel rel_sections[MAX_SECTIONS];
Elf64_Phdr *phdrs;
struct elf_writer_section *shstrtab_sec;
struct elf_writer_section *strtab_sec;
struct elf_writer_section *symtab_sec;
struct elf_writer_string_table strtab;
struct elf_writer_sym_table symtab;
int bit64;
};
static size_t section_index(struct elf_writer *ew,
struct elf_writer_section *sec)
{
return sec - &ew->sections[0];
}
static struct elf_writer_section *last_section(struct elf_writer *ew)
{
return &ew->sections[ew->num_secs - 1];
}
static void strtab_init(struct elf_writer *ew, size_t size)
{
struct buffer b;
Elf64_Shdr shdr;
/* Start adding strings after the initial NUL entry. */
ew->strtab.next_offset = 1;
ew->strtab.max_size = size;
ew->strtab.buffer = calloc(1, ew->strtab.max_size);
buffer_init(&b, NULL, ew->strtab.buffer, ew->strtab.max_size);
memset(&shdr, 0, sizeof(shdr));
shdr.sh_type = SHT_STRTAB;
shdr.sh_addralign = 1;
shdr.sh_size = ew->strtab.max_size;
elf_writer_add_section(ew, &shdr, &b, ".strtab");
ew->strtab_sec = last_section(ew);
}
static void symtab_init(struct elf_writer *ew, size_t max_entries)
{
struct buffer b;
Elf64_Shdr shdr;
memset(&shdr, 0, sizeof(shdr));
shdr.sh_type = SHT_SYMTAB;
if (ew->bit64) {
shdr.sh_entsize = sizeof(Elf64_Sym);
shdr.sh_addralign = sizeof(Elf64_Addr);
} else {
shdr.sh_entsize = sizeof(Elf32_Sym);
shdr.sh_addralign = sizeof(Elf32_Addr);
}
shdr.sh_size = shdr.sh_entsize * max_entries;
ew->symtab.syms = calloc(max_entries, sizeof(Elf64_Sym));
ew->symtab.num_entries = 1;
ew->symtab.max_entries = max_entries;
buffer_init(&b, NULL, ew->symtab.syms, shdr.sh_size);
elf_writer_add_section(ew, &shdr, &b, ".symtab");
ew->symtab_sec = last_section(ew);
}
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->shstrtab_sec = last_section(ew);
ew->ehdr.e_shstrndx = section_index(ew, ew->shstrtab_sec);
/* Add a small string table and symbol table. */
strtab_init(ew, 4096);
symtab_init(ew, 100);
return ew;
}
/*
* Clean up any internal state represented by ew. Aftewards the elf_writer
* is invalid.
* It is safe to call elf_writer_destroy with ew as NULL. It returns without
* performing any action.
*/
void elf_writer_destroy(struct elf_writer *ew)
{
int i;
if (ew == NULL)
return;
if (ew->phdrs != NULL)
free(ew->phdrs);
free(ew->strtab.buffer);
free(ew->symtab.syms);
for (i = 0; i < MAX_SECTIONS; i++)
free(ew->rel_sections[i].rels);
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);
}
}
static int section_consecutive(struct elf_writer *ew, Elf64_Half secidx)
{
Elf64_Half i;
struct elf_writer_section *prev_alloc = NULL;
if (secidx == 0)
return 0;
for (i = 0; i < secidx; i++) {
if (ew->sections[i].shdr.sh_flags & SHF_ALLOC)
prev_alloc = &ew->sections[i];
}
if (prev_alloc == NULL)
return 0;
if (prev_alloc->shdr.sh_addr + prev_alloc->shdr.sh_size ==
ew->sections[secidx].shdr.sh_addr)
return 1;
return 0;
}
static void write_phdrs(struct elf_writer *ew, struct buffer *phdrs)
{
Elf64_Half i;
Elf64_Phdr phdr;
size_t num_written = 0;
size_t num_needs_write = 0;
for (i = 0; i < ew->num_secs; i++) {
struct elf_writer_section *sec = &ew->sections[i];
if (!(sec->shdr.sh_flags & SHF_ALLOC))
continue;
if (!section_consecutive(ew, i)) {
/* Write out previously set phdr. */
if (num_needs_write != num_written) {
phdr_write(ew, phdrs, &phdr);
num_written++;
}
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;
num_needs_write++;
} else {
/* Accumulate file size and memsize. The assumption
* is that each section is either NOBITS or full
* (sh_size == file size). This is standard in that
* an ELF section doesn't have a file size component. */
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_filesz += buffer_size(&sec->content);
phdr.p_memsz += sec->shdr.sh_size;
}
}
/* Write out the last phdr. */
if (num_needs_write != num_written) {
phdr_write(ew, phdrs, &phdr);
num_written++;
}
assert(num_written == ew->ehdr.e_phnum);
}
static void fixup_symbol_table(struct elf_writer *ew)
{
struct elf_writer_section *sec = ew->symtab_sec;
/* If there is only the NULL section, mark section as inactive. */
if (ew->symtab.num_entries == 1) {
sec->shdr.sh_type = SHT_NULL;
sec->shdr.sh_size = 0;
} else {
size_t i;
struct buffer wr;
buffer_clone(&wr, &sec->content);
/* To appease xdr. */
buffer_set_size(&wr, 0);
for (i = 0; i < ew->symtab.num_entries; i++) {
/* Create local copy as were over-writing backing
* store of the symbol. */
Elf64_Sym sym = ew->symtab.syms[i];
if (ew->bit64) {
ew->xdr->put32(&wr, sym.st_name);
ew->xdr->put8(&wr, sym.st_info);
ew->xdr->put8(&wr, sym.st_other);
ew->xdr->put16(&wr, sym.st_shndx);
ew->xdr->put64(&wr, sym.st_value);
ew->xdr->put64(&wr, sym.st_size);
} else {
ew->xdr->put32(&wr, sym.st_name);
ew->xdr->put32(&wr, sym.st_value);
ew->xdr->put32(&wr, sym.st_size);
ew->xdr->put8(&wr, sym.st_info);
ew->xdr->put8(&wr, sym.st_other);
ew->xdr->put16(&wr, sym.st_shndx);
}
}
/* Update section size. */
sec->shdr.sh_size = sec->shdr.sh_entsize;
sec->shdr.sh_size *= ew->symtab.num_entries;
/* Fix up sh_link to point to string table. */
sec->shdr.sh_link = section_index(ew, ew->strtab_sec);
/* sh_info is supposed to be 1 greater than symbol table
* index of last local binding. Just use max symbols. */
sec->shdr.sh_info = ew->symtab.num_entries;
}
buffer_set_size(&sec->content, sec->shdr.sh_size);
}
static void fixup_relocations(struct elf_writer *ew)
{
int i;
Elf64_Xword type;
switch (ew->ehdr.e_machine) {
case EM_386:
type = R_386_32;
break;
case EM_ARM:
type = R_ARM_ABS32;
break;
case EM_AARCH64:
type = R_AARCH64_ABS64;
break;
case EM_MIPS:
type = R_MIPS_32;
break;
case EM_RISCV:
type = R_RISCV_32;
break;
case EM_PPC64:
type = R_PPC64_ADDR32;
break;
default:
ERROR("Unable to handle relocations for e_machine %x\n",
ew->ehdr.e_machine);
return;
}
for (i = 0; i < MAX_SECTIONS; i++) {
struct elf_writer_rel *rel_sec = &ew->rel_sections[i];
struct elf_writer_section *sec = rel_sec->sec;
struct buffer writer;
size_t j;
if (sec == NULL)
continue;
/* Update section header size as well as content size. */
buffer_init(&sec->content, sec->content.name, rel_sec->rels,
rel_sec->num_entries * sec->shdr.sh_entsize);
sec->shdr.sh_size = buffer_size(&sec->content);
buffer_clone(&writer, &sec->content);
/* To make xdr happy. */
buffer_set_size(&writer, 0);
for (j = 0; j < ew->rel_sections[i].num_entries; j++) {
/* Make copy as we're overwriting backing store. */
Elf64_Rel rel = rel_sec->rels[j];
rel.r_info = ELF64_R_INFO(ELF64_R_SYM(rel.r_info),
ELF64_R_TYPE(type));
if (ew->bit64) {
ew->xdr->put64(&writer, rel.r_offset);
ew->xdr->put64(&writer, rel.r_info);
} else {
Elf32_Rel rel32;
rel32.r_offset = rel.r_offset;
rel32.r_info =
ELF32_R_INFO(ELF64_R_SYM(rel.r_info),
ELF64_R_TYPE(rel.r_info));
ew->xdr->put32(&writer, rel32.r_offset);
ew->xdr->put32(&writer, rel32.r_info);
}
}
}
}
/*
* 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);
/* Perform any necessary work for special sections. */
fixup_symbol_table(ew);
fixup_relocations(ew);
/* 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) {
if (!section_consecutive(ew, i))
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_sec->content;
buffer_splice(strtab, out, shstroffset, shstrlen);
ew->shstrtab_sec->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++) {
struct elf_writer_section *sec = &ew->sections[i];
/* Update section offsets. Be sure to not update SHN_UNDEF. */
if (sec == ew->shstrtab_sec)
sec->shdr.sh_offset = shstroffset;
else if (i != SHN_UNDEF)
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);
/* Output section data for all sections but SHN_UNDEF and
* section header string table. */
if (i != SHN_UNDEF && sec != ew->shstrtab_sec)
bputs(&data, buffer_get(&sec->content),
buffer_size(&sec->content));
}
write_phdrs(ew, &phdrs);
return 0;
}
/* Add a string to the string table returning index on success, < 0 on error. */
static int elf_writer_add_string(struct elf_writer *ew, const char *new)
{
size_t current_offset;
size_t new_len;
for (current_offset = 0; current_offset < ew->strtab.next_offset; ) {
const char *str = ew->strtab.buffer + current_offset;
size_t len = strlen(str) + 1;
if (!strcmp(str, new))
return current_offset;
current_offset += len;
}
new_len = strlen(new) + 1;
if (current_offset + new_len > ew->strtab.max_size) {
ERROR("No space for string in .strtab.\n");
return -1;
}
memcpy(ew->strtab.buffer + current_offset, new, new_len);
ew->strtab.next_offset = current_offset + new_len;
return current_offset;
}
static int elf_writer_section_index(struct elf_writer *ew, const char *name)
{
size_t i;
for (i = 0; i < ew->num_secs; i++) {
if (ew->sections[i].name == NULL)
continue;
if (!strcmp(ew->sections[i].name, name))
return i;
}
ERROR("ELF Section not found: %s\n", name);
return -1;
}
int elf_writer_add_symbol(struct elf_writer *ew, const char *name,
const char *section_name,
Elf64_Addr value, Elf64_Word size,
int binding, int type)
{
int i;
Elf64_Sym sym = {
.st_value = value,
.st_size = size,
.st_info = ELF64_ST_INFO(binding, type),
};
if (ew->symtab.max_entries == ew->symtab.num_entries) {
ERROR("No more symbol entries left.\n");
return -1;
}
i = elf_writer_add_string(ew, name);
if (i < 0)
return -1;
sym.st_name = i;
i = elf_writer_section_index(ew, section_name);
if (i < 0)
return -1;
sym.st_shndx = i;
ew->symtab.syms[ew->symtab.num_entries++] = sym;
return 0;
}
static int elf_sym_index(struct elf_writer *ew, const char *sym)
{
int j;
size_t i;
Elf64_Word st_name;
/* Determine index of symbol in the string table. */
j = elf_writer_add_string(ew, sym);
if (j < 0)
return -1;
st_name = j;
for (i = 0; i < ew->symtab.num_entries; i++)
if (ew->symtab.syms[i].st_name == st_name)
return i;
return -1;
}
static struct elf_writer_rel *rel_section(struct elf_writer *ew,
const Elf64_Rel *r)
{
Elf64_Sym *sym;
struct elf_writer_rel *rel;
Elf64_Shdr shdr;
struct buffer b;
sym = &ew->symtab.syms[ELF64_R_SYM(r->r_info)];
/* Determine if section has been initialized yet. */
rel = &ew->rel_sections[sym->st_shndx];
if (rel->sec != NULL)
return rel;
memset(&shdr, 0, sizeof(shdr));
shdr.sh_type = SHT_REL;
shdr.sh_link = section_index(ew, ew->symtab_sec);
shdr.sh_info = sym->st_shndx;
if (ew->bit64) {
shdr.sh_addralign = sizeof(Elf64_Addr);
shdr.sh_entsize = sizeof(Elf64_Rel);
} else {
shdr.sh_addralign = sizeof(Elf32_Addr);
shdr.sh_entsize = sizeof(Elf32_Rel);
}
if ((strlen(".rel") + strlen(ew->sections[sym->st_shndx].name) + 1) >
MAX_REL_NAME) {
ERROR("Rel Section name won't fit\n");
return NULL;
}
strcat(rel->name, ".rel");
strcat(rel->name, ew->sections[sym->st_shndx].name);
buffer_init(&b, rel->name, NULL, 0);
elf_writer_add_section(ew, &shdr, &b, rel->name);
rel->sec = last_section(ew);
return rel;
}
static int add_rel(struct elf_writer_rel *rel_sec, const Elf64_Rel *rel)
{
if (rel_sec->num_entries == rel_sec->max_entries) {
size_t num = rel_sec->max_entries * 2;
Elf64_Rel *old_rels;
if (num == 0)
num = 128;
old_rels = rel_sec->rels;
rel_sec->rels = calloc(num, sizeof(Elf64_Rel));
memcpy(rel_sec->rels, old_rels,
rel_sec->num_entries * sizeof(Elf64_Rel));
free(old_rels);
rel_sec->max_entries = num;
}
rel_sec->rels[rel_sec->num_entries] = *rel;
rel_sec->num_entries++;
return 0;
}
int elf_writer_add_rel(struct elf_writer *ew, const char *sym, Elf64_Addr addr)
{
Elf64_Rel rel;
Elf64_Xword sym_info;
int sym_index;
struct elf_writer_rel *rel_sec;
sym_index = elf_sym_index(ew, sym);
if (sym_index < 0) {
ERROR("Unable to locate symbol: %s\n", sym);
return -1;
}
sym_info = sym_index;
/* The relocation type will get fixed prior to serialization. */
rel.r_offset = addr;
rel.r_info = ELF64_R_INFO(sym_info, 0);
rel_sec = rel_section(ew, &rel);
if (rel_sec == NULL)
return -1;
return add_rel(rel_sec, &rel);
}