diff options
| -rw-r--r-- | arch/i386/reloc.h | 26 | ||||
| -rw-r--r-- | arch/x86_64/reloc.h | 28 | ||||
| -rw-r--r-- | src/ldso/dynlink.c | 385 | ||||
| -rw-r--r-- | src/ldso/i386/start.s | 19 | ||||
| -rw-r--r-- | src/ldso/x86_64/start.s | 8 |
5 files changed, 466 insertions, 0 deletions
diff --git a/arch/i386/reloc.h b/arch/i386/reloc.h new file mode 100644 index 00000000..02b5fa02 --- /dev/null +++ b/arch/i386/reloc.h @@ -0,0 +1,26 @@ +#include <string.h> +#include <elf.h> + +#define IS_COPY(x) ((x)==R_386_COPY) + +static inline void do_single_reloc(size_t *reloc_addr, int type, size_t sym_val, size_t sym_size, unsigned char *base_addr, size_t addend) +{ + switch(type) { + case R_386_32: + *reloc_addr += sym_val; + break; + case R_386_PC32: + *reloc_addr += sym_val - (size_t)reloc_addr; + break; + case R_386_GLOB_DAT: + case R_386_JMP_SLOT: + *reloc_addr = sym_val; + break; + case R_386_RELATIVE: + *reloc_addr += (size_t)base_addr; + break; + case R_386_COPY: + memcpy(reloc_addr, (void *)sym_val, sym_size); + break; + } +} diff --git a/arch/x86_64/reloc.h b/arch/x86_64/reloc.h new file mode 100644 index 00000000..2db6115d --- /dev/null +++ b/arch/x86_64/reloc.h @@ -0,0 +1,28 @@ +#include <stdint.h> +#include <string.h> +#include <elf.h> + +#define IS_COPY(x) ((x)==R_X86_64_COPY) + +static inline void do_single_reloc(size_t *reloc_addr, int type, size_t sym_val, size_t sym_size, unsigned char *base_addr, size_t addend) +{ + switch(type) { + case R_X86_64_GLOB_DAT: + case R_X86_64_JUMP_SLOT: + case R_X86_64_64: + *reloc_addr = sym_val + addend; + break; + case R_X86_64_32: + *(uint32_t *)reloc_addr = sym_val + addend; + break; + case R_X86_64_PC32: + *reloc_addr = sym_val + addend - (size_t)reloc_addr + (size_t)base_addr; + break; + case R_X86_64_RELATIVE: + *reloc_addr = (size_t)base_addr + addend; + break; + case R_X86_64_COPY: + memcpy(reloc_addr, (void *)sym_val, sym_size); + break; + } +} diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c new file mode 100644 index 00000000..b4444252 --- /dev/null +++ b/src/ldso/dynlink.c @@ -0,0 +1,385 @@ +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> +#include <stdint.h> +#include <elf.h> +#include <sys/mman.h> +#include <limits.h> +#include <stdint.h> +#include <fcntl.h> +#include <sys/stat.h> +#include <errno.h> +#include <limits.h> +#include <elf.h> + +#include "reloc.h" + +#if ULONG_MAX == 0xffffffff +typedef Elf32_Ehdr Ehdr; +typedef Elf32_Phdr Phdr; +typedef Elf32_Sym Sym; +#define R_TYPE(x) ((x)&255) +#define R_SYM(x) ((x)>>8) +#else +typedef Elf64_Ehdr Ehdr; +typedef Elf64_Phdr Phdr; +typedef Elf64_Sym Sym; +#define R_TYPE(x) ((x)&0xffffffff) +#define R_SYM(x) ((x)>>32) +#endif + +struct dso +{ + struct dso *next, *prev; + int refcnt; + size_t *dynv; + Sym *syms; + size_t *hashtab; + char *strings; + unsigned char *base; + unsigned char *map; + size_t map_len; + dev_t dev; + ino_t ino; + int global; + int relocated; + char name[]; +}; + +static struct dso *head, *tail, *libc; + +#define AUX_CNT 15 +#define DYN_CNT 34 + +static void decode_vec(size_t *v, size_t *a, size_t cnt) +{ + memset(a, 0, cnt*sizeof(size_t)); + for (; v[0]; v+=2) if (v[0]<cnt) { + a[0] |= 1ULL<<v[0]; + a[v[0]] = v[1]; + } +} + +static uint32_t hash(const char *s) +{ + uint_fast32_t h = 0; + while (*s) { + h = 16*h + *s++; + h ^= h>>24 & 0xf0; + } + return h & 0xfffffff; +} + +static Sym *lookup(const char *s, uint32_t h, Sym *syms, size_t *hashtab, char *strings) +{ + size_t i; + for (i=hashtab[2+h%hashtab[0]]; i; i=hashtab[2+hashtab[0]+i]) { + if (!strcmp(s, strings+syms[i].st_name)) + return syms+i; + } + return 0; +} + +#define OK_TYPES (1<<STT_NOTYPE | 1<<STT_OBJECT | 1<<STT_FUNC | 1<<STT_COMMON) + +static void *find_sym(struct dso *dso, const char *s, int need_def) +{ + uint32_t h = hash(s); + for (; dso; dso=dso->next) { + Sym *sym = lookup(s, h, dso->syms, dso->hashtab, dso->strings); + if (sym && (!need_def || sym->st_shndx) && sym->st_value + && (1<<(sym->st_info&0xf) & OK_TYPES)) + return dso->base + sym->st_value; + } + return 0; +} + +static void do_relocs(unsigned char *base, size_t *rel, size_t rel_size, size_t stride, Sym *syms, char *strings, struct dso *dso) +{ + Sym *sym; + const char *name; + size_t sym_val, sym_size; + size_t *reloc_addr; + void *ctx; + int type; + int sym_index; + + for (; rel_size; rel+=stride, rel_size-=stride*sizeof(size_t)) { + reloc_addr = (void *)(base + rel[0]); + type = R_TYPE(rel[1]); + sym_index = R_SYM(rel[1]); + if (sym_index) { + sym = syms + sym_index; + name = strings + sym->st_name; + ctx = IS_COPY(type) ? dso->next : dso; + sym_val = (size_t)find_sym(ctx, name, 1); + sym_size = sym->st_size; + } + do_single_reloc(reloc_addr, type, sym_val, sym_size, base, rel[2]); + } +} + +static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dynp) +{ + size_t buf[896/sizeof(size_t)]; + size_t phsize; + size_t addr_min=SIZE_MAX, addr_max=0, map_len; + size_t this_min, this_max; + off_t off_start; + Ehdr *eh; + Phdr *ph; + unsigned prot; + unsigned char *map, *base; + size_t dyn; + size_t i; + + ssize_t l = read(fd, buf, sizeof buf); + if (l<sizeof *eh) return 0; + eh = (void *)buf; + phsize = eh->e_phentsize * eh->e_phnum; + if (phsize + sizeof *eh > l) return 0; + if (eh->e_phoff + phsize > l) { + l = pread(fd, buf+sizeof *eh, phsize, eh->e_phoff); + if (l != phsize) return 0; + eh->e_phoff = sizeof *eh; + } + ph = (void *)((char *)buf + eh->e_phoff); + for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) { + if (ph->p_type == PT_DYNAMIC) + dyn = ph->p_vaddr; + if (ph->p_type != PT_LOAD) continue; + if (ph->p_vaddr < addr_min) { + addr_min = ph->p_vaddr; + off_start = ph->p_offset; + prot = (((ph->p_flags&PF_R) ? PROT_READ : 0) | + ((ph->p_flags&PF_W) ? PROT_WRITE: 0) | + ((ph->p_flags&PF_X) ? PROT_EXEC : 0)); + } + if (ph->p_vaddr+ph->p_memsz > addr_max) { + addr_max = ph->p_vaddr+ph->p_memsz; + } + } + if (!dyn) return 0; + addr_max += PAGE_SIZE-1; + addr_max &= -PAGE_SIZE; + addr_min &= -PAGE_SIZE; + off_start &= -PAGE_SIZE; + map_len = addr_max - addr_min + off_start; + /* The first time, we map too much, possibly even more than + * the length of the file. This is okay because we will not + * use the invalid part; we just need to reserve the right + * amount of virtual address space to map over later. */ + map = mmap(0, map_len, prot, MAP_PRIVATE, fd, off_start); + if (map==MAP_FAILED) return 0; + base = map - addr_min; + ph = (void *)((char *)buf + eh->e_phoff); + for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) { + if (ph->p_type != PT_LOAD) continue; + /* Reuse the existing mapping for the lowest-address LOAD */ + if ((ph->p_vaddr & -PAGE_SIZE) == addr_min) continue; + this_min = ph->p_vaddr & -PAGE_SIZE; + this_max = ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE; + off_start = ph->p_offset & -PAGE_SIZE; + prot = (((ph->p_flags&PF_R) ? PROT_READ : 0) | + ((ph->p_flags&PF_W) ? PROT_WRITE: 0) | + ((ph->p_flags&PF_X) ? PROT_EXEC : 0)); + if (mmap(base+this_min, this_max-this_min, prot, MAP_PRIVATE|MAP_FIXED, fd, off_start) == MAP_FAILED) { + munmap(map, map_len); + return 0; + } + if (ph->p_memsz > ph->p_filesz) { + size_t brk = (size_t)base+ph->p_vaddr+ph->p_filesz; + size_t pgbrk = brk+PAGE_SIZE-1 & -PAGE_SIZE; + memset((void *)brk, 0, pgbrk-brk & PAGE_SIZE-1); + if (pgbrk-(size_t)base < this_max && mmap((void *)pgbrk, (size_t)base+this_max-pgbrk, prot, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) == MAP_FAILED) { + munmap(map, map_len); + return 0; + } + } + } + *lenp = map_len; + *basep = base; + *dynp = dyn; + return map; +} + +static struct dso *load_library(const char *name) +{ + unsigned char *base, *map; + size_t dyno, map_len; + struct dso *p; + size_t dyn[DYN_CNT] = {0}; + int fd; + struct stat st; + + /* Catch and block attempts to reload the implementation itself */ + if (name[0]=='l' && name[1]=='i' && name[2]=='b') { + static const char *rp, reserved[] = + "c\0pthread\0rt\0m\0dl\0util\0xnet\0"; + char *z = strchr(name, '.'); + if (z) { + size_t l = z-name; + for (rp=reserved; *rp && memcmp(name+3, rp, l-3); rp+=strlen(rp)+1); + if (*rp) { + if (!libc->prev) { + tail->next = libc; + libc->prev = tail; + tail = libc; + } + return libc; + } + } + } + /* Search for the name to see if it's already loaded */ + for (p=head->next; p; p=p->next) { + if (!strcmp(p->name, name)) { + p->refcnt++; + return p; + } + } + if (name[0] == '/') { + fd = open(name, O_RDONLY); + } else { + static const char path[] = "/lib/\0/usr/local/lib/\0/usr/lib/\0"; + const char *s; + char buf[NAME_MAX+32]; + if (strlen(name) > NAME_MAX || strchr(name, '/')) return 0; + for (s=path; *s; s+=strlen(s)+1) { + strcpy(buf, s); + strcat(buf, name); + if ((fd = open(buf, O_RDONLY))>=0) break; + } + } + if (fd < 0) return 0; + if (fstat(fd, &st) < 0) { + close(fd); + return 0; + } + for (p=head->next; p; p=p->next) { + if (p->dev == st.st_dev && p->ino == st.st_ino) { + close(fd); + p->refcnt++; + return p; + } + } + map = map_library(fd, &map_len, &base, &dyno); + close(fd); + if (!map) return 0; + p = calloc(1, sizeof *p + strlen(name) + 1); + if (!p) { + munmap(map, map_len); + return 0; + } + + p->map = map; + p->map_len = map_len; + p->base = base; + p->dynv = (void *)(base + dyno); + decode_vec(p->dynv, dyn, DYN_CNT); + + p->syms = (void *)(base + dyn[DT_SYMTAB]); + p->hashtab = (void *)(base + dyn[DT_HASH]); + p->strings = (void *)(base + dyn[DT_STRTAB]); + p->dev = st.st_dev; + p->ino = st.st_ino; + p->global = 1; + p->refcnt = 1; + strcpy(p->name, name); + + tail->next = p; + p->prev = tail; + tail = p; + + return p; +} + +static void load_deps(struct dso *p) +{ + size_t i; + for (; p; p=p->next) { + for (i=0; p->dynv[i]; i+=2) { + if (p->dynv[i] != DT_NEEDED) continue; + load_library(p->strings + p->dynv[i+1]); + } + } +} + +static void reloc_all(struct dso *p) +{ + size_t dyn[DYN_CNT] = {0}; + for (; p; p=p->next) { + if (p->relocated) continue; + decode_vec(p->dynv, dyn, DYN_CNT); + do_relocs(p->base, (void *)(p->base+dyn[DT_JMPREL]), dyn[DT_PLTRELSZ], + 2+(dyn[DT_PLTREL]==DT_RELA), p->syms, p->strings, p); + do_relocs(p->base, (void *)(p->base+dyn[DT_REL]), dyn[DT_RELSZ], + 2, p->syms, p->strings, p); + do_relocs(p->base, (void *)(p->base+dyn[DT_RELA]), dyn[DT_RELASZ], + 3, p->syms, p->strings, p); + } +} + +void *__dynlink(int argc, char **argv, size_t *got) +{ + size_t *auxv, aux[AUX_CNT] = {0}; + size_t app_dyn[DYN_CNT] = {0}; + size_t lib_dyn[DYN_CNT] = {0}; + size_t i; + Phdr *phdr; + struct dso lib, app; + + /* Find aux vector just past environ[] */ + for (i=argc+1; argv[i]; i++); + auxv = (void *)(argv+i+1); + + decode_vec(auxv, aux, AUX_CNT); + + /* Relocate ldso's DYNAMIC pointer and load vector */ + decode_vec((void *)(got[0] += aux[AT_BASE]), lib_dyn, DYN_CNT); + + /* Find the program image's DYNAMIC section and decode it */ + phdr = (void *)aux[AT_PHDR]; + for (i=aux[AT_PHNUM]; i--; phdr=(void *)((char *)phdr + aux[AT_PHENT])) { + if (phdr->p_type == PT_DYNAMIC) { + decode_vec((void *)phdr->p_vaddr, app_dyn, DYN_CNT); + break; + } + } + + app = (struct dso){ + .base = 0, + .strings = (void *)(app_dyn[DT_STRTAB]), + .hashtab = (void *)(app_dyn[DT_HASH]), + .syms = (void *)(app_dyn[DT_SYMTAB]), + .dynv = (void *)(phdr->p_vaddr), + .next = &lib + }; + + lib = (struct dso){ + .base = (void *)aux[AT_BASE], + .strings = (void *)(aux[AT_BASE]+lib_dyn[DT_STRTAB]), + .hashtab = (void *)(aux[AT_BASE]+lib_dyn[DT_HASH]), + .syms = (void *)(aux[AT_BASE]+lib_dyn[DT_SYMTAB]), + .dynv = (void *)(got[0]), + .relocated = 1 + }; + + /* Relocate the dynamic linker/libc */ + do_relocs((void *)aux[AT_BASE], (void *)(aux[AT_BASE]+lib_dyn[DT_REL]), + lib_dyn[DT_RELSZ], 2, lib.syms, lib.strings, &app); + do_relocs((void *)aux[AT_BASE], (void *)(aux[AT_BASE]+lib_dyn[DT_RELA]), + lib_dyn[DT_RELASZ], 3, lib.syms, lib.strings, &app); + + /* At this point the standard library is fully functional */ + + head = tail = &app; + libc = &lib; + app.next = 0; + load_deps(head); + + reloc_all(head); + + errno = 0; + return (void *)aux[AT_ENTRY]; +} diff --git a/src/ldso/i386/start.s b/src/ldso/i386/start.s new file mode 100644 index 00000000..47c2748b --- /dev/null +++ b/src/ldso/i386/start.s @@ -0,0 +1,19 @@ +.text +.global _start +_start: + xorl %ebp,%ebp + popl %ecx + movl %esp,%eax + andl $-16,%esp + movl %eax,%esi + movl %ecx,%edi + pushl %ebp + call 1f +1: addl $_GLOBAL_OFFSET_TABLE_,(%esp) + pushl %eax + pushl %ecx + call __dynlink + movl %esi,%esp + pushl %edi + xorl %edx,%edx + jmp *%eax diff --git a/src/ldso/x86_64/start.s b/src/ldso/x86_64/start.s new file mode 100644 index 00000000..efb27454 --- /dev/null +++ b/src/ldso/x86_64/start.s @@ -0,0 +1,8 @@ +.text +.global _start +_start: + mov (%rsp),%rdi + lea 8(%rsp),%rsi + lea _GLOBAL_OFFSET_TABLE_(%rip),%rdx + call __dynlink + jmp *%rax |