minix/lib/libexec/exec_elf.c

#define _SYSTEM 1

#include <minix/type.h>
#include <minix/const.h>
#include <sys/param.h>
#include <assert.h>
#include <unistd.h>
#include <errno.h>
#include <libexec.h>
#include <string.h>
#include <machine/elf.h>

/* For verbose logging */
#define ELF_DEBUG 0

/* Support only 32-bit ELF objects */
#define __ELF_WORD_SIZE 32

#define SECTOR_SIZE 512

static int check_header(const Elf_Ehdr *hdr);

static int elf_sane(const Elf_Ehdr *hdr)
{
  if (check_header(hdr) != OK) {
     return 0;
  }

  if((hdr->e_type != ET_EXEC) && (hdr->e_type != ET_DYN)) {
     return 0;
  }

  if ((hdr->e_phoff > SECTOR_SIZE) ||
      (hdr->e_phoff + hdr->e_phentsize * hdr->e_phnum) > SECTOR_SIZE) {
#if ELF_DEBUG
	printf("peculiar phoff\n");
#endif
     return 0;
  }

  return 1;
}

static int elf_ph_sane(const Elf_Phdr *phdr)
{
  if (rounddown((uintptr_t)phdr, sizeof(Elf_Addr)) != (uintptr_t)phdr) {
     return 0;
  }
  return 1;
}

static int elf_unpack(const char *exec_hdr,
	int hdr_len, const Elf_Ehdr **hdr, const Elf_Phdr **phdr)
{
  *hdr = (const Elf_Ehdr *)exec_hdr;
  if(!elf_sane(*hdr)) {
#if ELF_DEBUG
	printf("elf_sane failed\n");
#endif
  	return ENOEXEC;
  }
  *phdr = (const Elf_Phdr *)(exec_hdr + (*hdr)->e_phoff);
  if(!elf_ph_sane(*phdr)) {
#if ELF_DEBUG
	printf("elf_ph_sane failed\n");
#endif
  	return ENOEXEC;
  }
#if 0
  if((int)((*phdr) + (*hdr)->e_phnum) >= hdr_len) return ENOEXEC;
#endif
  return OK;
}

int read_header_elf(
  const char *exec_hdr,		/* executable header */
  int hdr_len,			/* significant bytes in exec_hdr */
  vir_bytes *text_vaddr,	/* text virtual address */
  phys_bytes *text_paddr,	/* text physical address */
  vir_bytes *text_filebytes,	/* text segment size (in the file) */
  vir_bytes *text_membytes,	/* text segment size (in memory) */
  vir_bytes *data_vaddr,	/* data virtual address */
  phys_bytes *data_paddr,	/* data physical address */
  vir_bytes *data_filebytes,	/* data segment size (in the file) */
  vir_bytes *data_membytes,	/* data segment size (in memory) */
  vir_bytes *pc,		/* program entry point (initial PC) */
  off_t *text_offset,		/* file offset to text segment */
  off_t *data_offset		/* file offset to data segment */
)
{
  const Elf_Ehdr *hdr = NULL;
  const Elf_Phdr *phdr = NULL;
  unsigned long seg_filebytes, seg_membytes;
  int e, i = 0;

  *text_vaddr = *text_paddr = 0;
  *text_filebytes = *text_membytes = 0;
  *data_vaddr = *data_paddr = 0;
  *data_filebytes = *data_membytes = 0;
  *pc = *text_offset = *data_offset = 0;

  if((e=elf_unpack(exec_hdr, hdr_len, &hdr, &phdr)) != OK) {
#if ELF_DEBUG
	printf("elf_unpack failed\n");
#endif
  	return e;
   }

#if ELF_DEBUG
  printf("Program header file offset (phoff): %ld\n", hdr->e_phoff);
  printf("Section header file offset (shoff): %ld\n", hdr->e_shoff);
  printf("Program header entry size (phentsize): %d\n", hdr->e_phentsize);
  printf("Program header entry num (phnum): %d\n", hdr->e_phnum);
  printf("Section header entry size (shentsize): %d\n", hdr->e_shentsize);
  printf("Section header entry num (shnum): %d\n", hdr->e_shnum);
  printf("Section name strings index (shstrndx): %d\n", hdr->e_shstrndx);
  printf("Entry Point: 0x%lx\n", hdr->e_entry);
#endif

  for (i = 0; i < hdr->e_phnum; i++) {
      switch (phdr[i].p_type) {
      case PT_LOAD:
	  if (phdr[i].p_memsz == 0)
	      break;
	  seg_filebytes = phdr[i].p_filesz;
	  seg_membytes = round_page(phdr[i].p_memsz + phdr[i].p_vaddr -
				    trunc_page(phdr[i].p_vaddr));

	  if (hdr->e_entry >= phdr[i].p_vaddr &&
	      hdr->e_entry < (phdr[i].p_vaddr + phdr[i].p_memsz)) {
	      *text_vaddr = phdr[i].p_vaddr;
	      *text_paddr = phdr[i].p_paddr;
	      *text_filebytes = seg_filebytes;
	      *text_membytes = seg_membytes;
	      *pc = (vir_bytes)hdr->e_entry;
	      *text_offset = phdr[i].p_offset;
	  } else {
	      *data_vaddr = phdr[i].p_vaddr;
	      *data_paddr = phdr[i].p_paddr;
	      *data_filebytes = seg_filebytes;
	      *data_membytes = seg_membytes;
	      *data_offset = phdr[i].p_offset;
	  }
	  break;
      default:
	  break;
      }
  }

#if ELF_DEBUG
  printf("Text vaddr:     0x%lx\n", *text_vaddr);
  printf("Text paddr:     0x%lx\n", *text_paddr);
  printf("Text filebytes: 0x%lx\n", *text_filebytes);
  printf("Text membytes:  0x%lx\n", *text_membytes);
  printf("Data vaddr:     0x%lx\n", *data_vaddr);
  printf("Data paddr:     0x%lx\n", *data_paddr);
  printf("Data filebyte:  0x%lx\n", *data_filebytes);
  printf("Data membytes:  0x%lx\n", *data_membytes);
  printf("PC:             0x%lx\n", *pc);
  printf("Text offset:    0x%lx\n", *text_offset);
  printf("Data offset:    0x%lx\n", *data_offset);
#endif

  return OK;
}

#define IS_ELF(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)

static int check_header(const Elf_Ehdr *hdr)
{
  if (!IS_ELF(*hdr) ||
      hdr->e_ident[EI_DATA] != ELF_TARG_DATA ||
      hdr->e_ident[EI_VERSION] != EV_CURRENT ||
      hdr->e_phentsize != sizeof(Elf_Phdr) ||
      hdr->e_version != ELF_TARG_VER)
      return ENOEXEC;

  return OK;
}

int elf_phdr(const char *exec_hdr, int hdr_len, vir_bytes *ret_phdr)
{
  const Elf_Ehdr *hdr = NULL;
  const Elf_Phdr *phdr = NULL;
  int e, i, have_computed_phdr = 1;

  if((e=elf_unpack(exec_hdr, hdr_len, &hdr, &phdr)) != OK) return e;

  for (i = 0; i < hdr->e_phnum; i++) {
      switch (phdr[i].p_type) {
      case PT_LOAD:
      		/* compute phdr based on this heuristic, to be used
		 * if there is no PT_PHDR
		 */
      		if(phdr[i].p_offset == 0) {
			*ret_phdr = phdr[i].p_vaddr + hdr->e_phoff;
			have_computed_phdr = 1;
		}
		break;
      case PT_PHDR:
      	  *ret_phdr = phdr[i].p_vaddr;
	  return OK;
      default:
	  break;;
      }
  }
  if(have_computed_phdr) return OK;
  return ENOENT;
}

/* Return >0 if there is an ELF interpreter (i.e. it is a dynamically linked
 * executable) and we could extract it successfully.
 * Return 0 if there isn't one.
 * Return <0 on error.
 */
int elf_has_interpreter(const char *exec_hdr,		/* executable header */
		int hdr_len, char *interp, int maxsz)
{
  const Elf_Ehdr *hdr = NULL;
  const Elf_Phdr *phdr = NULL;
  int e, i;

  if((e=elf_unpack(exec_hdr, hdr_len, &hdr, &phdr)) != OK) return e;

  for (i = 0; i < hdr->e_phnum; i++) {
      switch (phdr[i].p_type) {
      case PT_INTERP:
      	  if(!interp) return 1;
      	  if(phdr[i].p_filesz >= maxsz)
	  	return -1;
	  if(phdr[i].p_offset + phdr[i].p_filesz >= hdr_len)
	  	return -1;
	  memcpy(interp, exec_hdr + phdr[i].p_offset, phdr[i].p_filesz);
	  interp[phdr[i].p_filesz] = '\0';
	  return 1;
      default:
	  continue;
      }
  }
  return 0;
}