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0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  * genelf.c
0004  * Copyright (C) 2014, Google, Inc
0005  *
0006  * Contributed by:
0007  *  Stephane Eranian <eranian@gmail.com>
0008  */
0009 
0010 #include <sys/types.h>
0011 #include <stddef.h>
0012 #include <libelf.h>
0013 #include <string.h>
0014 #include <stdlib.h>
0015 #include <unistd.h>
0016 #include <inttypes.h>
0017 #include <fcntl.h>
0018 #include <err.h>
0019 #ifdef HAVE_DWARF_SUPPORT
0020 #include <dwarf.h>
0021 #endif
0022 
0023 #include "genelf.h"
0024 #include "../util/jitdump.h"
0025 #include <linux/compiler.h>
0026 
0027 #ifndef NT_GNU_BUILD_ID
0028 #define NT_GNU_BUILD_ID 3
0029 #endif
0030 
0031 #define BUILD_ID_URANDOM /* different uuid for each run */
0032 
0033 #ifdef HAVE_LIBCRYPTO_SUPPORT
0034 
0035 #define BUILD_ID_MD5
0036 #undef BUILD_ID_SHA /* does not seem to work well when linked with Java */
0037 #undef BUILD_ID_URANDOM /* different uuid for each run */
0038 
0039 #ifdef BUILD_ID_SHA
0040 #include <openssl/sha.h>
0041 #endif
0042 
0043 #ifdef BUILD_ID_MD5
0044 #include <openssl/evp.h>
0045 #include <openssl/md5.h>
0046 #endif
0047 #endif
0048 
0049 
0050 typedef struct {
0051   unsigned int namesz;  /* Size of entry's owner string */
0052   unsigned int descsz;  /* Size of the note descriptor */
0053   unsigned int type;    /* Interpretation of the descriptor */
0054   char         name[0]; /* Start of the name+desc data */
0055 } Elf_Note;
0056 
0057 struct options {
0058     char *output;
0059     int fd;
0060 };
0061 
0062 static char shd_string_table[] = {
0063     0,
0064     '.', 't', 'e', 'x', 't', 0,         /*  1 */
0065     '.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', 0, /*  7 */
0066     '.', 's', 'y', 'm', 't', 'a', 'b', 0,       /* 17 */
0067     '.', 's', 't', 'r', 't', 'a', 'b', 0,       /* 25 */
0068     '.', 'n', 'o', 't', 'e', '.', 'g', 'n', 'u', '.', 'b', 'u', 'i', 'l', 'd', '-', 'i', 'd', 0, /* 33 */
0069     '.', 'd', 'e', 'b', 'u', 'g', '_', 'l', 'i', 'n', 'e', 0, /* 52 */
0070     '.', 'd', 'e', 'b', 'u', 'g', '_', 'i', 'n', 'f', 'o', 0, /* 64 */
0071     '.', 'd', 'e', 'b', 'u', 'g', '_', 'a', 'b', 'b', 'r', 'e', 'v', 0, /* 76 */
0072     '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', '_', 'h', 'd', 'r', 0, /* 90 */
0073     '.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', 0, /* 104 */
0074 };
0075 
0076 static struct buildid_note {
0077     Elf_Note desc;      /* descsz: size of build-id, must be multiple of 4 */
0078     char     name[4];   /* GNU\0 */
0079     char     build_id[20];
0080 } bnote;
0081 
0082 static Elf_Sym symtab[]={
0083     /* symbol 0 MUST be the undefined symbol */
0084     { .st_name  = 0, /* index in sym_string table */
0085       .st_info  = ELF_ST_TYPE(STT_NOTYPE),
0086       .st_shndx = 0, /* for now */
0087       .st_value = 0x0,
0088       .st_other = ELF_ST_VIS(STV_DEFAULT),
0089       .st_size  = 0,
0090     },
0091     { .st_name  = 1, /* index in sym_string table */
0092       .st_info  = ELF_ST_BIND(STB_LOCAL) | ELF_ST_TYPE(STT_FUNC),
0093       .st_shndx = 1,
0094       .st_value = 0, /* for now */
0095       .st_other = ELF_ST_VIS(STV_DEFAULT),
0096       .st_size  = 0, /* for now */
0097     }
0098 };
0099 
0100 #ifdef BUILD_ID_URANDOM
0101 static void
0102 gen_build_id(struct buildid_note *note,
0103          unsigned long load_addr __maybe_unused,
0104          const void *code __maybe_unused,
0105          size_t csize __maybe_unused)
0106 {
0107     int fd;
0108     size_t sz = sizeof(note->build_id);
0109     ssize_t sret;
0110 
0111     fd = open("/dev/urandom", O_RDONLY);
0112     if (fd == -1)
0113         err(1, "cannot access /dev/urandom for buildid");
0114 
0115     sret = read(fd, note->build_id, sz);
0116 
0117     close(fd);
0118 
0119     if (sret != (ssize_t)sz)
0120         memset(note->build_id, 0, sz);
0121 }
0122 #endif
0123 
0124 #ifdef BUILD_ID_SHA
0125 static void
0126 gen_build_id(struct buildid_note *note,
0127          unsigned long load_addr __maybe_unused,
0128          const void *code,
0129          size_t csize)
0130 {
0131     if (sizeof(note->build_id) < SHA_DIGEST_LENGTH)
0132         errx(1, "build_id too small for SHA1");
0133 
0134     SHA1(code, csize, (unsigned char *)note->build_id);
0135 }
0136 #endif
0137 
0138 #ifdef BUILD_ID_MD5
0139 static void
0140 gen_build_id(struct buildid_note *note, unsigned long load_addr, const void *code, size_t csize)
0141 {
0142     EVP_MD_CTX *mdctx;
0143 
0144     if (sizeof(note->build_id) < 16)
0145         errx(1, "build_id too small for MD5");
0146 
0147     mdctx = EVP_MD_CTX_new();
0148     if (!mdctx)
0149         errx(2, "failed to create EVP_MD_CTX");
0150 
0151     EVP_DigestInit_ex(mdctx, EVP_md5(), NULL);
0152     EVP_DigestUpdate(mdctx, &load_addr, sizeof(load_addr));
0153     EVP_DigestUpdate(mdctx, code, csize);
0154     EVP_DigestFinal_ex(mdctx, (unsigned char *)note->build_id, NULL);
0155     EVP_MD_CTX_free(mdctx);
0156 }
0157 #endif
0158 
0159 static int
0160 jit_add_eh_frame_info(Elf *e, void* unwinding, uint64_t unwinding_header_size,
0161               uint64_t unwinding_size, uint64_t base_offset)
0162 {
0163     Elf_Data *d;
0164     Elf_Scn *scn;
0165     Elf_Shdr *shdr;
0166     uint64_t unwinding_table_size = unwinding_size - unwinding_header_size;
0167 
0168     /*
0169      * setup eh_frame section
0170      */
0171     scn = elf_newscn(e);
0172     if (!scn) {
0173         warnx("cannot create section");
0174         return -1;
0175     }
0176 
0177     d = elf_newdata(scn);
0178     if (!d) {
0179         warnx("cannot get new data");
0180         return -1;
0181     }
0182 
0183     d->d_align = 8;
0184     d->d_off = 0LL;
0185     d->d_buf = unwinding;
0186     d->d_type = ELF_T_BYTE;
0187     d->d_size = unwinding_table_size;
0188     d->d_version = EV_CURRENT;
0189 
0190     shdr = elf_getshdr(scn);
0191     if (!shdr) {
0192         warnx("cannot get section header");
0193         return -1;
0194     }
0195 
0196     shdr->sh_name = 104;
0197     shdr->sh_type = SHT_PROGBITS;
0198     shdr->sh_addr = base_offset;
0199     shdr->sh_flags = SHF_ALLOC;
0200     shdr->sh_entsize = 0;
0201 
0202     /*
0203      * setup eh_frame_hdr section
0204      */
0205     scn = elf_newscn(e);
0206     if (!scn) {
0207         warnx("cannot create section");
0208         return -1;
0209     }
0210 
0211     d = elf_newdata(scn);
0212     if (!d) {
0213         warnx("cannot get new data");
0214         return -1;
0215     }
0216 
0217     d->d_align = 4;
0218     d->d_off = 0LL;
0219     d->d_buf = unwinding + unwinding_table_size;
0220     d->d_type = ELF_T_BYTE;
0221     d->d_size = unwinding_header_size;
0222     d->d_version = EV_CURRENT;
0223 
0224     shdr = elf_getshdr(scn);
0225     if (!shdr) {
0226         warnx("cannot get section header");
0227         return -1;
0228     }
0229 
0230     shdr->sh_name = 90;
0231     shdr->sh_type = SHT_PROGBITS;
0232     shdr->sh_addr = base_offset + unwinding_table_size;
0233     shdr->sh_flags = SHF_ALLOC;
0234     shdr->sh_entsize = 0;
0235 
0236     return 0;
0237 }
0238 
0239 /*
0240  * fd: file descriptor open for writing for the output file
0241  * load_addr: code load address (could be zero, just used for buildid)
0242  * sym: function name (for native code - used as the symbol)
0243  * code: the native code
0244  * csize: the code size in bytes
0245  */
0246 int
0247 jit_write_elf(int fd, uint64_t load_addr, const char *sym,
0248           const void *code, int csize,
0249           void *debug __maybe_unused, int nr_debug_entries __maybe_unused,
0250           void *unwinding, uint64_t unwinding_header_size, uint64_t unwinding_size)
0251 {
0252     Elf *e;
0253     Elf_Data *d;
0254     Elf_Scn *scn;
0255     Elf_Ehdr *ehdr;
0256     Elf_Phdr *phdr;
0257     Elf_Shdr *shdr;
0258     uint64_t eh_frame_base_offset;
0259     char *strsym = NULL;
0260     int symlen;
0261     int retval = -1;
0262 
0263     if (elf_version(EV_CURRENT) == EV_NONE) {
0264         warnx("ELF initialization failed");
0265         return -1;
0266     }
0267 
0268     e = elf_begin(fd, ELF_C_WRITE, NULL);
0269     if (!e) {
0270         warnx("elf_begin failed");
0271         goto error;
0272     }
0273 
0274     /*
0275      * setup ELF header
0276      */
0277     ehdr = elf_newehdr(e);
0278     if (!ehdr) {
0279         warnx("cannot get ehdr");
0280         goto error;
0281     }
0282 
0283     ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN;
0284     ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS;
0285     ehdr->e_machine = GEN_ELF_ARCH;
0286     ehdr->e_type = ET_DYN;
0287     ehdr->e_entry = GEN_ELF_TEXT_OFFSET;
0288     ehdr->e_version = EV_CURRENT;
0289     ehdr->e_shstrndx= unwinding ? 4 : 2; /* shdr index for section name */
0290 
0291     /*
0292      * setup program header
0293      */
0294     phdr = elf_newphdr(e, 1);
0295     phdr[0].p_type = PT_LOAD;
0296     phdr[0].p_offset = 0;
0297     phdr[0].p_vaddr = 0;
0298     phdr[0].p_paddr = 0;
0299     phdr[0].p_filesz = csize;
0300     phdr[0].p_memsz = csize;
0301     phdr[0].p_flags = PF_X | PF_R;
0302     phdr[0].p_align = 8;
0303 
0304     /*
0305      * setup text section
0306      */
0307     scn = elf_newscn(e);
0308     if (!scn) {
0309         warnx("cannot create section");
0310         goto error;
0311     }
0312 
0313     d = elf_newdata(scn);
0314     if (!d) {
0315         warnx("cannot get new data");
0316         goto error;
0317     }
0318 
0319     d->d_align = 16;
0320     d->d_off = 0LL;
0321     d->d_buf = (void *)code;
0322     d->d_type = ELF_T_BYTE;
0323     d->d_size = csize;
0324     d->d_version = EV_CURRENT;
0325 
0326     shdr = elf_getshdr(scn);
0327     if (!shdr) {
0328         warnx("cannot get section header");
0329         goto error;
0330     }
0331 
0332     shdr->sh_name = 1;
0333     shdr->sh_type = SHT_PROGBITS;
0334     shdr->sh_addr = GEN_ELF_TEXT_OFFSET;
0335     shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
0336     shdr->sh_entsize = 0;
0337 
0338     /*
0339      * Setup .eh_frame_hdr and .eh_frame
0340      */
0341     if (unwinding) {
0342         eh_frame_base_offset = ALIGN_8(GEN_ELF_TEXT_OFFSET + csize);
0343         retval = jit_add_eh_frame_info(e, unwinding,
0344                            unwinding_header_size, unwinding_size,
0345                            eh_frame_base_offset);
0346         if (retval)
0347             goto error;
0348     }
0349 
0350     /*
0351      * setup section headers string table
0352      */
0353     scn = elf_newscn(e);
0354     if (!scn) {
0355         warnx("cannot create section");
0356         goto error;
0357     }
0358 
0359     d = elf_newdata(scn);
0360     if (!d) {
0361         warnx("cannot get new data");
0362         goto error;
0363     }
0364 
0365     d->d_align = 1;
0366     d->d_off = 0LL;
0367     d->d_buf = shd_string_table;
0368     d->d_type = ELF_T_BYTE;
0369     d->d_size = sizeof(shd_string_table);
0370     d->d_version = EV_CURRENT;
0371 
0372     shdr = elf_getshdr(scn);
0373     if (!shdr) {
0374         warnx("cannot get section header");
0375         goto error;
0376     }
0377 
0378     shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */
0379     shdr->sh_type = SHT_STRTAB;
0380     shdr->sh_flags = 0;
0381     shdr->sh_entsize = 0;
0382 
0383     /*
0384      * setup symtab section
0385      */
0386     symtab[1].st_size  = csize;
0387     symtab[1].st_value = GEN_ELF_TEXT_OFFSET;
0388 
0389     scn = elf_newscn(e);
0390     if (!scn) {
0391         warnx("cannot create section");
0392         goto error;
0393     }
0394 
0395     d = elf_newdata(scn);
0396     if (!d) {
0397         warnx("cannot get new data");
0398         goto error;
0399     }
0400 
0401     d->d_align = 8;
0402     d->d_off = 0LL;
0403     d->d_buf = symtab;
0404     d->d_type = ELF_T_SYM;
0405     d->d_size = sizeof(symtab);
0406     d->d_version = EV_CURRENT;
0407 
0408     shdr = elf_getshdr(scn);
0409     if (!shdr) {
0410         warnx("cannot get section header");
0411         goto error;
0412     }
0413 
0414     shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */
0415     shdr->sh_type = SHT_SYMTAB;
0416     shdr->sh_flags = 0;
0417     shdr->sh_entsize = sizeof(Elf_Sym);
0418     shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */
0419 
0420     /*
0421      * setup symbols string table
0422      * 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry
0423      */
0424     symlen = 2 + strlen(sym);
0425     strsym = calloc(1, symlen);
0426     if (!strsym) {
0427         warnx("cannot allocate strsym");
0428         goto error;
0429     }
0430     strcpy(strsym + 1, sym);
0431 
0432     scn = elf_newscn(e);
0433     if (!scn) {
0434         warnx("cannot create section");
0435         goto error;
0436     }
0437 
0438     d = elf_newdata(scn);
0439     if (!d) {
0440         warnx("cannot get new data");
0441         goto error;
0442     }
0443 
0444     d->d_align = 1;
0445     d->d_off = 0LL;
0446     d->d_buf = strsym;
0447     d->d_type = ELF_T_BYTE;
0448     d->d_size = symlen;
0449     d->d_version = EV_CURRENT;
0450 
0451     shdr = elf_getshdr(scn);
0452     if (!shdr) {
0453         warnx("cannot get section header");
0454         goto error;
0455     }
0456 
0457     shdr->sh_name = 25; /* offset in shd_string_table */
0458     shdr->sh_type = SHT_STRTAB;
0459     shdr->sh_flags = 0;
0460     shdr->sh_entsize = 0;
0461 
0462     /*
0463      * setup build-id section
0464      */
0465     scn = elf_newscn(e);
0466     if (!scn) {
0467         warnx("cannot create section");
0468         goto error;
0469     }
0470 
0471     d = elf_newdata(scn);
0472     if (!d) {
0473         warnx("cannot get new data");
0474         goto error;
0475     }
0476 
0477     /*
0478      * build-id generation
0479      */
0480     gen_build_id(&bnote, load_addr, code, csize);
0481     bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */
0482     bnote.desc.descsz = sizeof(bnote.build_id);
0483     bnote.desc.type   = NT_GNU_BUILD_ID;
0484     strcpy(bnote.name, "GNU");
0485 
0486     d->d_align = 4;
0487     d->d_off = 0LL;
0488     d->d_buf = &bnote;
0489     d->d_type = ELF_T_BYTE;
0490     d->d_size = sizeof(bnote);
0491     d->d_version = EV_CURRENT;
0492 
0493     shdr = elf_getshdr(scn);
0494     if (!shdr) {
0495         warnx("cannot get section header");
0496         goto error;
0497     }
0498 
0499     shdr->sh_name = 33; /* offset in shd_string_table */
0500     shdr->sh_type = SHT_NOTE;
0501     shdr->sh_addr = 0x0;
0502     shdr->sh_flags = SHF_ALLOC;
0503     shdr->sh_size = sizeof(bnote);
0504     shdr->sh_entsize = 0;
0505 
0506 #ifdef HAVE_DWARF_SUPPORT
0507     if (debug && nr_debug_entries) {
0508         retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries);
0509         if (retval)
0510             goto error;
0511     } else
0512 #endif
0513     {
0514         if (elf_update(e, ELF_C_WRITE) < 0) {
0515             warnx("elf_update 4 failed");
0516             goto error;
0517         }
0518     }
0519 
0520     retval = 0;
0521 error:
0522     (void)elf_end(e);
0523 
0524     free(strsym);
0525 
0526 
0527     return retval;
0528 }
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