// SPDX-License-Identifier: GPL-2.0-only
/*
* genelf.c
* Copyright (C) 2014, Google, Inc
*
* Contributed by:
* Stephane Eranian <[email protected]>
*/
#include <sys/types.h>
#include <stddef.h>
#include <libelf.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <inttypes.h>
#include <fcntl.h>
#include <err.h>
#ifdef HAVE_DWARF_SUPPORT
#include <dwarf.h>
#endif
#include "genelf.h"
#include "../util/jitdump.h"
#include <linux/compiler.h>
#ifndef NT_GNU_BUILD_ID
#define NT_GNU_BUILD_ID 3
#endif
#define BUILD_ID_URANDOM /* different uuid for each run */
#ifdef HAVE_LIBCRYPTO_SUPPORT
#define BUILD_ID_MD5
#undef BUILD_ID_SHA /* does not seem to work well when linked with Java */
#undef BUILD_ID_URANDOM /* different uuid for each run */
#ifdef BUILD_ID_SHA
#include <openssl/sha.h>
#endif
#ifdef BUILD_ID_MD5
#include <openssl/evp.h>
#include <openssl/md5.h>
#endif
#endif
typedef struct {
unsigned int namesz; /* Size of entry's owner string */
unsigned int descsz; /* Size of the note descriptor */
unsigned int type; /* Interpretation of the descriptor */
char name[0]; /* Start of the name+desc data */
} Elf_Note;
static char shd_string_table[] = {
0,
'.', 't', 'e', 'x', 't', 0, /* 1 */
'.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', 0, /* 7 */
'.', 's', 'y', 'm', 't', 'a', 'b', 0, /* 17 */
'.', 's', 't', 'r', 't', 'a', 'b', 0, /* 25 */
'.', 'n', 'o', 't', 'e', '.', 'g', 'n', 'u', '.', 'b', 'u', 'i', 'l', 'd', '-', 'i', 'd', 0, /* 33 */
'.', 'd', 'e', 'b', 'u', 'g', '_', 'l', 'i', 'n', 'e', 0, /* 52 */
'.', 'd', 'e', 'b', 'u', 'g', '_', 'i', 'n', 'f', 'o', 0, /* 64 */
'.', 'd', 'e', 'b', 'u', 'g', '_', 'a', 'b', 'b', 'r', 'e', 'v', 0, /* 76 */
'.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', '_', 'h', 'd', 'r', 0, /* 90 */
'.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', 0, /* 104 */
};
static struct buildid_note {
Elf_Note desc; /* descsz: size of build-id, must be multiple of 4 */
char name[4]; /* GNU\0 */
char build_id[20];
} bnote;
static Elf_Sym symtab[]={
/* symbol 0 MUST be the undefined symbol */
{ .st_name = 0, /* index in sym_string table */
.st_info = ELF_ST_TYPE(STT_NOTYPE),
.st_shndx = 0, /* for now */
.st_value = 0x0,
.st_other = ELF_ST_VIS(STV_DEFAULT),
.st_size = 0,
},
{ .st_name = 1, /* index in sym_string table */
.st_info = ELF_ST_BIND(STB_LOCAL) | ELF_ST_TYPE(STT_FUNC),
.st_shndx = 1,
.st_value = 0, /* for now */
.st_other = ELF_ST_VIS(STV_DEFAULT),
.st_size = 0, /* for now */
}
};
#ifdef BUILD_ID_URANDOM
static void
gen_build_id(struct buildid_note *note,
unsigned long load_addr __maybe_unused,
const void *code __maybe_unused,
size_t csize __maybe_unused)
{
int fd;
size_t sz = sizeof(note->build_id);
ssize_t sret;
fd = open("/dev/urandom", O_RDONLY);
if (fd == -1)
err(1, "cannot access /dev/urandom for buildid");
sret = read(fd, note->build_id, sz);
close(fd);
if (sret != (ssize_t)sz)
memset(note->build_id, 0, sz);
}
#endif
#ifdef BUILD_ID_SHA
static void
gen_build_id(struct buildid_note *note,
unsigned long load_addr __maybe_unused,
const void *code,
size_t csize)
{
if (sizeof(note->build_id) < SHA_DIGEST_LENGTH)
errx(1, "build_id too small for SHA1");
SHA1(code, csize, (unsigned char *)note->build_id);
}
#endif
#ifdef BUILD_ID_MD5
static void
gen_build_id(struct buildid_note *note, unsigned long load_addr, const void *code, size_t csize)
{
EVP_MD_CTX *mdctx;
if (sizeof(note->build_id) < 16)
errx(1, "build_id too small for MD5");
mdctx = EVP_MD_CTX_new();
if (!mdctx)
errx(2, "failed to create EVP_MD_CTX");
EVP_DigestInit_ex(mdctx, EVP_md5(), NULL);
EVP_DigestUpdate(mdctx, &load_addr, sizeof(load_addr));
EVP_DigestUpdate(mdctx, code, csize);
EVP_DigestFinal_ex(mdctx, (unsigned char *)note->build_id, NULL);
EVP_MD_CTX_free(mdctx);
}
#endif
static int
jit_add_eh_frame_info(Elf *e, void* unwinding, uint64_t unwinding_header_size,
uint64_t unwinding_size, uint64_t base_offset)
{
Elf_Data *d;
Elf_Scn *scn;
Elf_Shdr *shdr;
uint64_t unwinding_table_size = unwinding_size - unwinding_header_size;
/*
* setup eh_frame section
*/
scn = elf_newscn(e);
if (!scn) {
warnx("cannot create section");
return -1;
}
d = elf_newdata(scn);
if (!d) {
warnx("cannot get new data");
return -1;
}
d->d_align = 8;
d->d_off = 0LL;
d->d_buf = unwinding;
d->d_type = ELF_T_BYTE;
d->d_size = unwinding_table_size;
d->d_version = EV_CURRENT;
shdr = elf_getshdr(scn);
if (!shdr) {
warnx("cannot get section header");
return -1;
}
shdr->sh_name = 104;
shdr->sh_type = SHT_PROGBITS;
shdr->sh_addr = base_offset;
shdr->sh_flags = SHF_ALLOC;
shdr->sh_entsize = 0;
/*
* setup eh_frame_hdr section
*/
scn = elf_newscn(e);
if (!scn) {
warnx("cannot create section");
return -1;
}
d = elf_newdata(scn);
if (!d) {
warnx("cannot get new data");
return -1;
}
d->d_align = 4;
d->d_off = 0LL;
d->d_buf = unwinding + unwinding_table_size;
d->d_type = ELF_T_BYTE;
d->d_size = unwinding_header_size;
d->d_version = EV_CURRENT;
shdr = elf_getshdr(scn);
if (!shdr) {
warnx("cannot get section header");
return -1;
}
shdr->sh_name = 90;
shdr->sh_type = SHT_PROGBITS;
shdr->sh_addr = base_offset + unwinding_table_size;
shdr->sh_flags = SHF_ALLOC;
shdr->sh_entsize = 0;
return 0;
}
/*
* fd: file descriptor open for writing for the output file
* load_addr: code load address (could be zero, just used for buildid)
* sym: function name (for native code - used as the symbol)
* code: the native code
* csize: the code size in bytes
*/
int
jit_write_elf(int fd, uint64_t load_addr, const char *sym,
const void *code, int csize,
void *debug __maybe_unused, int nr_debug_entries __maybe_unused,
void *unwinding, uint64_t unwinding_header_size, uint64_t unwinding_size)
{
Elf *e;
Elf_Data *d;
Elf_Scn *scn;
Elf_Ehdr *ehdr;
Elf_Phdr *phdr;
Elf_Shdr *shdr;
uint64_t eh_frame_base_offset;
char *strsym = NULL;
int symlen;
int retval = -1;
if (elf_version(EV_CURRENT) == EV_NONE) {
warnx("ELF initialization failed");
return -1;
}
e = elf_begin(fd, ELF_C_WRITE, NULL);
if (!e) {
warnx("elf_begin failed");
goto error;
}
/*
* setup ELF header
*/
ehdr = elf_newehdr(e);
if (!ehdr) {
warnx("cannot get ehdr");
goto error;
}
ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN;
ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS;
ehdr->e_machine = GEN_ELF_ARCH;
ehdr->e_type = ET_DYN;
ehdr->e_entry = GEN_ELF_TEXT_OFFSET;
ehdr->e_version = EV_CURRENT;
ehdr->e_shstrndx= unwinding ? 4 : 2; /* shdr index for section name */
/*
* setup program header
*/
phdr = elf_newphdr(e, 1);
phdr[0].p_type = PT_LOAD;
phdr[0].p_offset = GEN_ELF_TEXT_OFFSET;
phdr[0].p_vaddr = GEN_ELF_TEXT_OFFSET;
phdr[0].p_paddr = GEN_ELF_TEXT_OFFSET;
phdr[0].p_filesz = csize;
phdr[0].p_memsz = csize;
phdr[0].p_flags = PF_X | PF_R;
phdr[0].p_align = 8;
/*
* setup text section
*/
scn = elf_newscn(e);
if (!scn) {
warnx("cannot create section");
goto error;
}
d = elf_newdata(scn);
if (!d) {
warnx("cannot get new data");
goto error;
}
d->d_align = 16;
d->d_off = 0LL;
d->d_buf = (void *)code;
d->d_type = ELF_T_BYTE;
d->d_size = csize;
d->d_version = EV_CURRENT;
shdr = elf_getshdr(scn);
if (!shdr) {
warnx("cannot get section header");
goto error;
}
shdr->sh_name = 1;
shdr->sh_type = SHT_PROGBITS;
shdr->sh_addr = GEN_ELF_TEXT_OFFSET;
shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
shdr->sh_entsize = 0;
/*
* Setup .eh_frame_hdr and .eh_frame
*/
if (unwinding) {
eh_frame_base_offset = ALIGN_8(GEN_ELF_TEXT_OFFSET + csize);
retval = jit_add_eh_frame_info(e, unwinding,
unwinding_header_size, unwinding_size,
eh_frame_base_offset);
if (retval)
goto error;
retval = -1;
}
/*
* setup section headers string table
*/
scn = elf_newscn(e);
if (!scn) {
warnx("cannot create section");
goto error;
}
d = elf_newdata(scn);
if (!d) {
warnx("cannot get new data");
goto error;
}
d->d_align = 1;
d->d_off = 0LL;
d->d_buf = shd_string_table;
d->d_type = ELF_T_BYTE;
d->d_size = sizeof(shd_string_table);
d->d_version = EV_CURRENT;
shdr = elf_getshdr(scn);
if (!shdr) {
warnx("cannot get section header");
goto error;
}
shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */
shdr->sh_type = SHT_STRTAB;
shdr->sh_flags = 0;
shdr->sh_entsize = 0;
/*
* setup symtab section
*/
symtab[1].st_size = csize;
symtab[1].st_value = GEN_ELF_TEXT_OFFSET;
scn = elf_newscn(e);
if (!scn) {
warnx("cannot create section");
goto error;
}
d = elf_newdata(scn);
if (!d) {
warnx("cannot get new data");
goto error;
}
d->d_align = 8;
d->d_off = 0LL;
d->d_buf = symtab;
d->d_type = ELF_T_SYM;
d->d_size = sizeof(symtab);
d->d_version = EV_CURRENT;
shdr = elf_getshdr(scn);
if (!shdr) {
warnx("cannot get section header");
goto error;
}
shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */
shdr->sh_type = SHT_SYMTAB;
shdr->sh_flags = 0;
shdr->sh_entsize = sizeof(Elf_Sym);
shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */
/*
* setup symbols string table
* 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry
*/
symlen = 2 + strlen(sym);
strsym = calloc(1, symlen);
if (!strsym) {
warnx("cannot allocate strsym");
goto error;
}
strcpy(strsym + 1, sym);
scn = elf_newscn(e);
if (!scn) {
warnx("cannot create section");
goto error;
}
d = elf_newdata(scn);
if (!d) {
warnx("cannot get new data");
goto error;
}
d->d_align = 1;
d->d_off = 0LL;
d->d_buf = strsym;
d->d_type = ELF_T_BYTE;
d->d_size = symlen;
d->d_version = EV_CURRENT;
shdr = elf_getshdr(scn);
if (!shdr) {
warnx("cannot get section header");
goto error;
}
shdr->sh_name = 25; /* offset in shd_string_table */
shdr->sh_type = SHT_STRTAB;
shdr->sh_flags = 0;
shdr->sh_entsize = 0;
/*
* setup build-id section
*/
scn = elf_newscn(e);
if (!scn) {
warnx("cannot create section");
goto error;
}
d = elf_newdata(scn);
if (!d) {
warnx("cannot get new data");
goto error;
}
/*
* build-id generation
*/
gen_build_id(&bnote, load_addr, code, csize);
bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */
bnote.desc.descsz = sizeof(bnote.build_id);
bnote.desc.type = NT_GNU_BUILD_ID;
strcpy(bnote.name, "GNU");
d->d_align = 4;
d->d_off = 0LL;
d->d_buf = &bnote;
d->d_type = ELF_T_BYTE;
d->d_size = sizeof(bnote);
d->d_version = EV_CURRENT;
shdr = elf_getshdr(scn);
if (!shdr) {
warnx("cannot get section header");
goto error;
}
shdr->sh_name = 33; /* offset in shd_string_table */
shdr->sh_type = SHT_NOTE;
shdr->sh_addr = 0x0;
shdr->sh_flags = SHF_ALLOC;
shdr->sh_size = sizeof(bnote);
shdr->sh_entsize = 0;
#ifdef HAVE_DWARF_SUPPORT
if (debug && nr_debug_entries) {
retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries);
if (retval)
goto error;
} else
#endif
{
if (elf_update(e, ELF_C_WRITE) < 0) {
warnx("elf_update 4 failed");
goto error;
}
}
retval = 0;
error:
(void)elf_end(e);
free(strsym);
return retval;
}
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