coregrind/ume.c

/*--------------------------------------------------------------------*/
/*--- User-mode execve(), and other stuff shared between stage1    ---*/
/*--- and stage2.                                            ume.c ---*/
/*--------------------------------------------------------------------*/

/*
   This file is part of Valgrind, a dynamic binary instrumentation
   framework.

   Copyright (C) 2000-2005 Julian Seward 
      jseward@acm.org

   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; either version 2 of the
   License, or (at your option) any later version.

   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.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307, USA.

   The GNU General Public License is contained in the file COPYING.
*/


#define _GNU_SOURCE
#define _FILE_OFFSET_BITS 64

#include "core.h"

#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>

#include "ume.h"

#if	ELFSZ == 64
#define ESZ(x)	Elf64_##x
#elif	ELFSZ == 32
#define ESZ(x)	Elf32_##x
#else
#error ELFSZ needs to ==32 or ==64
#endif

struct elfinfo
{
   ESZ(Ehdr)	e;
   ESZ(Phdr)	*p;
   int		fd;
};

static void check_mmap(void* res, void* base, int len)
{
   if ((void*)-1 == res) {
      fprintf(stderr, "valgrind: mmap(%p, %d) failed in UME.\n", base, len);
      exit(1);
   }
}

// 'extra' allows the caller to pass in extra args to 'fn', like free
// variables to a closure.
void foreach_map(int (*fn)(char *start, char *end,
			   const char *perm, off_t offset,
			   int maj, int min, int ino, void* extra),
                 void* extra)
{
   static char buf[10240];
   char *bufptr = buf;
   int ret, fd;

   fd = open("/proc/self/maps", O_RDONLY);

   if (fd == -1) {
      perror("open /proc/self/maps");
      return;
   }

   ret = read(fd, buf, sizeof(buf));

   if (ret == -1) {
      perror("read /proc/self/maps");
      close(fd);
      return;
   }
   close(fd);

   if (ret == sizeof(buf)) {
      fprintf(stderr, "buf too small\n");
      return;
   }

   while(bufptr && bufptr < buf+ret) {
      char perm[5];
      ULong offset;
      int maj, min;
      int ino;
      void *segstart, *segend;

      sscanf(bufptr, "%p-%p %s %llx %x:%x %d",
	     &segstart, &segend, perm, &offset, &maj, &min, &ino);
      bufptr = strchr(bufptr, '\n');
      if (bufptr != NULL)
	 bufptr++; /* skip \n */

      if (!(*fn)(segstart, segend, perm, offset, maj, min, ino, extra))
	 break;
   }
}

/*------------------------------------------------------------*/
/*--- Finding auxv on the stack                            ---*/
/*------------------------------------------------------------*/

struct ume_auxv *find_auxv(UWord* sp)
{
   sp++;                // skip argc (Nb: is word-sized, not int-sized!)

   while (*sp != 0)     // skip argv
      sp++;
   sp++;

   while (*sp != 0)     // skip env
      sp++;
   sp++;
   
   return (struct ume_auxv *)sp;
}

/*------------------------------------------------------------*/
/*--- Loading ELF files                                    ---*/
/*------------------------------------------------------------*/

static 
struct elfinfo *readelf(int fd, const char *filename)
{
   struct elfinfo *e = malloc(sizeof(*e));
   int phsz;

   assert(e);
   e->fd = fd;

   if (pread(fd, &e->e, sizeof(e->e), 0) != sizeof(e->e)) {
      fprintf(stderr, "valgrind: %s: can't read ELF header: %s\n", 
	      filename, strerror(errno));
      return NULL;
   }

   if (memcmp(&e->e.e_ident[0], ELFMAG, SELFMAG) != 0) {
      fprintf(stderr, "valgrind: %s: bad ELF magic number\n", filename);
      return NULL;
   }
   if (e->e.e_ident[EI_CLASS] != VGA_ELF_CLASS) {
      fprintf(stderr, 
              "valgrind: wrong ELF executable class "
              "(eg. 32-bit instead of 64-bit)\n");
      return NULL;
   }
   if (e->e.e_ident[EI_DATA] != VGA_ELF_ENDIANNESS) {
      fprintf(stderr, "valgrind: executable has wrong endian-ness\n");
      return NULL;
   }
   if (!(e->e.e_type == ET_EXEC || e->e.e_type == ET_DYN)) {
      fprintf(stderr, "valgrind: this is not an executable\n");
      return NULL;
   }

   if (e->e.e_machine != VGA_ELF_MACHINE) {
      fprintf(stderr, "valgrind: executable is not for "
                      "this architecture\n");
      return NULL;
   }

   if (e->e.e_phentsize != sizeof(ESZ(Phdr))) {
      fprintf(stderr, "valgrind: sizeof ELF Phdr wrong\n");
      return NULL;
   }

   phsz = sizeof(ESZ(Phdr)) * e->e.e_phnum;
   e->p = malloc(phsz);
   assert(e->p);

   if (pread(fd, e->p, phsz, e->e.e_phoff) != phsz) {
      fprintf(stderr, "valgrind: can't read phdr: %s\n", strerror(errno));
      return NULL;
   }

   return e;
}

/* Map an ELF file.  Returns the brk address. */
static
ESZ(Addr) mapelf(struct elfinfo *e, ESZ(Addr) base)
{
   int i;
   void* res;
   ESZ(Addr) elfbrk = 0;

   for(i = 0; i < e->e.e_phnum; i++) {
      ESZ(Phdr) *ph = &e->p[i];
      ESZ(Addr) addr, brkaddr;
      ESZ(Word) memsz;

      if (ph->p_type != PT_LOAD)
	 continue;

      addr    = ph->p_vaddr+base;
      memsz   = ph->p_memsz;
      brkaddr = addr+memsz;

      if (brkaddr > elfbrk)
	 elfbrk = brkaddr;
   }

   for(i = 0; i < e->e.e_phnum; i++) {
      ESZ(Phdr) *ph = &e->p[i];
      ESZ(Addr) addr, bss, brkaddr;
      ESZ(Off) off;
      ESZ(Word) filesz;
      ESZ(Word) memsz;
      unsigned prot = 0;

      if (ph->p_type != PT_LOAD)
	 continue;

      if (ph->p_flags & PF_X) prot |= PROT_EXEC;
      if (ph->p_flags & PF_W) prot |= PROT_WRITE;
      if (ph->p_flags & PF_R) prot |= PROT_READ;

      addr    = ph->p_vaddr+base;
      off     = ph->p_offset;
      filesz  = ph->p_filesz;
      bss     = addr+filesz;
      memsz   = ph->p_memsz;
      brkaddr = addr+memsz;

      // Tom says: In the following, do what the Linux kernel does and only
      // map the pages that are required instead of rounding everything to
      // the specified alignment (ph->p_align).  (AMD64 doesn't work if you
      // use ph->p_align -- part of stage2's memory gets trashed somehow.)
      //
      // The condition handles the case of a zero-length segment.
      if (PGROUNDUP(bss)-PGROUNDDN(addr) > 0) {
         res = mmap((char *)PGROUNDDN(addr), PGROUNDUP(bss)-PGROUNDDN(addr),
                    prot, MAP_FIXED|MAP_PRIVATE, e->fd, PGROUNDDN(off));
         check_mmap(res, (char*)PGROUNDDN(addr),
                    PGROUNDUP(bss)-PGROUNDDN(addr));
      }

      // if memsz > filesz, fill the remainder with zeroed pages
      if (memsz > filesz) {
	 UInt bytes;

	 bytes = PGROUNDUP(brkaddr)-PGROUNDUP(bss);
	 if (bytes > 0) {
	    res = mmap((char *)PGROUNDUP(bss), bytes,
		       prot, MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
            check_mmap(res, (char*)PGROUNDUP(bss), bytes);
         }

	 bytes = bss & (VKI_PAGE_SIZE - 1);

         // The 'prot' condition allows for a read-only bss
         if ((prot & PROT_WRITE) && (bytes > 0)) {
	    bytes = VKI_PAGE_SIZE - bytes;
	    memset((char *)bss, 0, bytes);
	 }
      }
   }

   return elfbrk;
}

// Forward declaration.
static int do_exec_inner(const char *exe, struct exeinfo *info);

static int match_ELF(const char *hdr, int len)
{
   ESZ(Ehdr) *e = (ESZ(Ehdr) *)hdr;
   return (len > sizeof(*e)) && memcmp(&e->e_ident[0], ELFMAG, SELFMAG) == 0;
}

static int load_ELF(char *hdr, int len, int fd, const char *name,
                    struct exeinfo *info)
{
   struct elfinfo *e;
   struct elfinfo *interp = NULL;
   ESZ(Addr) minaddr = ~0;	/* lowest mapped address */
   ESZ(Addr) maxaddr = 0;	/* highest mapped address */
   ESZ(Addr) interp_addr = 0;	/* interpreter (ld.so) address */
   ESZ(Word) interp_size = 0;	/* interpreter size */
   ESZ(Word) interp_align = VKI_PAGE_SIZE;
   int i;
   void *entry;
   ESZ(Addr) ebase = 0;

#ifdef HAVE_PIE
   ebase = info->exe_base;
#endif

   e = readelf(fd, name);

   if (e == NULL)
      return ENOEXEC;

   info->phnum = e->e.e_phnum;
   info->entry = e->e.e_entry + ebase;
   info->phdr = 0;

   for(i = 0; i < e->e.e_phnum; i++) {
      ESZ(Phdr) *ph = &e->p[i];

      switch(ph->p_type) {
      case PT_PHDR:
	 info->phdr = ph->p_vaddr + ebase;
	 break;

      case PT_LOAD:
	 if (ph->p_vaddr < minaddr)
	    minaddr = ph->p_vaddr;
	 if (ph->p_vaddr+ph->p_memsz > maxaddr)
	    maxaddr = ph->p_vaddr+ph->p_memsz;
	 break;
			
      case PT_INTERP: {
	 char *buf = malloc(ph->p_filesz+1);
	 int j;
	 int intfd;
	 int baseaddr_set;

         assert(buf);
	 pread(fd, buf, ph->p_filesz, ph->p_offset);
	 buf[ph->p_filesz] = '\0';

	 intfd = open(buf, O_RDONLY);
	 if (intfd == -1) {
	    perror("open interp");
	    exit(1);
	 }

	 interp = readelf(intfd, buf);
	 if (interp == NULL) {
	    fprintf(stderr, "Can't read interpreter\n");
	    return 1;
	 }
	 free(buf);

	 baseaddr_set = 0;
	 for(j = 0; j < interp->e.e_phnum; j++) {
	    ESZ(Phdr) *iph = &interp->p[j];
	    ESZ(Addr) end;

	    if (iph->p_type != PT_LOAD)
	       continue;
	    
	    if (!baseaddr_set) {
	       interp_addr  = iph->p_vaddr;
	       interp_align = iph->p_align;
	       baseaddr_set = 1;
	    }

	    /* assumes that all segments in the interp are close */
	    end = (iph->p_vaddr - interp_addr) + iph->p_memsz;

	    if (end > interp_size)
	       interp_size = end;
	 }
	 break;

      default:
         // do nothing
         break;
      }
      }
   }

   if (info->phdr == 0)
      info->phdr = minaddr + e->e.e_phoff;

   if (info->exe_base != info->exe_end) {
      if (minaddr >= maxaddr ||
	  (minaddr + ebase < info->exe_base ||
	   maxaddr + ebase > info->exe_end)) {
	 fprintf(stderr, "Executable range %p-%p is outside the\n"
                         "acceptable range %p-%p\n",
		 (void *)minaddr + ebase, (void *)maxaddr + ebase,
		 (void *)info->exe_base,  (void *)info->exe_end);
	 return ENOMEM;
      }
   }

   info->brkbase = mapelf(e, ebase);	/* map the executable */

   if (info->brkbase == 0)
      return ENOMEM;

   if (interp != NULL) {
      /* reserve a chunk of address space for interpreter */
      void* res;
      char* base = (char *)info->exe_base;
      char* baseoff;
      int flags = MAP_PRIVATE|MAP_ANONYMOUS;

      if (info->map_base != 0) {
	 base = (char *)ROUNDUP(info->map_base, interp_align);
	 flags |= MAP_FIXED;
      }

      res = mmap(base, interp_size, PROT_NONE, flags, -1, 0);
      check_mmap(res, base, interp_size);
      base = res;

      baseoff = base - interp_addr;

      mapelf(interp, (ESZ(Addr))baseoff);

      close(interp->fd);

      entry = baseoff + interp->e.e_entry;
      info->interp_base = (ESZ(Addr))base;

      free(interp->p);
      free(interp);
   } else
      entry = (void *)e->e.e_entry;

   info->exe_base = minaddr + ebase;
   info->exe_end  = maxaddr + ebase;

   info->init_eip = (Addr)entry;

   free(e->p);
   free(e);

   return 0;
}


static int match_script(const char *hdr, Int len)
{
   return (len > 2) && memcmp(hdr, "#!", 2) == 0;
}

static int load_script(char *hdr, int len, int fd, const char *name,
                       struct exeinfo *info)
{
   char *interp;
   char *const end = hdr+len;
   char *cp;
   char *arg = NULL;
   int eol;

   interp = hdr + 2;
   while(interp < end && (*interp == ' ' || *interp == '\t'))
      interp++;

   if (*interp != '/')
      return ENOEXEC;		/* absolute path only for interpreter */

   /* skip over interpreter name */
   for(cp = interp; cp < end && *cp != ' ' && *cp != '\t' && *cp != '\n'; cp++)
      ;

   eol = (*cp == '\n');

   *cp++ = '\0';

   if (!eol && cp < end) {
      /* skip space before arg */
      while (cp < end && (*cp == '\t' || *cp == ' '))
	 cp++;

      /* arg is from here to eol */
      arg = cp;
      while (cp < end && *cp != '\n')
	 cp++;
      *cp = '\0';
   }
   
   info->interp_name = strdup(interp);
   assert(NULL != info->interp_name);
   if (arg != NULL && *arg != '\0') {
      info->interp_args = strdup(arg);
      assert(NULL != info->interp_args);
   }

   if (info->argv && info->argv[0] != NULL)
      info->argv[0] = (char *)name;

   if (0)
      printf("#! script: interp_name=\"%s\" interp_args=\"%s\"\n",
	     info->interp_name, info->interp_args);

   return do_exec_inner(interp, info);
}

/* 
   Emulate the normal Unix permissions checking algorithm.

   If owner matches, then use the owner permissions, else
   if group matches, then use the group permissions, else
   use other permissions.

   Note that we can't deal with SUID/SGID, so we refuse to run them
   (otherwise the executable may misbehave if it doesn't have the
   permissions it thinks it does).
*/
static int check_perms(int fd)
{
   struct stat st;

   if (fstat(fd, &st) == -1) 
      return errno;

   if (st.st_mode & (S_ISUID | S_ISGID)) {
      //fprintf(stderr, "Can't execute suid/sgid executable %s\n", exe);
      return EACCES;
   }

   if (geteuid() == st.st_uid) {
      if (!(st.st_mode & S_IXUSR))
	 return EACCES;
   } else {
      int grpmatch = 0;

      if (getegid() == st.st_gid)
	 grpmatch = 1;
      else {
	 gid_t groups[32];
	 int ngrp = getgroups(32, groups);
	 int i;

	 for(i = 0; i < ngrp; i++)
	    if (groups[i] == st.st_gid) {
	       grpmatch = 1;
	       break;
	    }
      }

      if (grpmatch) {
	 if (!(st.st_mode & S_IXGRP))
	    return EACCES;
      } else if (!(st.st_mode & S_IXOTH))
	 return EACCES;
   }

   return 0;
}

static int do_exec_inner(const char *exe, struct exeinfo *info)
{
   int fd;
   int err;
   char buf[VKI_PAGE_SIZE];
   int bufsz;
   int i;
   int ret;
   static const struct {
      int (*match)(const char *hdr, int len);
      int (*load) (      char *hdr, int len, int fd2, const char *name,
                         struct exeinfo *);
   } formats[] = {
      { match_ELF,    load_ELF },
      { match_script, load_script },
   };

   fd = open(exe, O_RDONLY);
   if (fd == -1) {
      if (0)
	 fprintf(stderr, "Can't open executable %s: %s\n",
		 exe, strerror(errno));
      return errno;
   }

   err = check_perms(fd);
   if (err != 0) {
      close(fd);
      return err;
   }

   bufsz = pread(fd, buf, sizeof(buf), 0);
   if (bufsz < 0) {
      fprintf(stderr, "Can't read executable header: %s\n",
	      strerror(errno));
      close(fd);
      return errno;
   }

   ret = ENOEXEC;
   for(i = 0; i < sizeof(formats)/sizeof(*formats); i++) {
      if ((formats[i].match)(buf, bufsz)) {
	 ret = (formats[i].load)(buf, bufsz, fd, exe, info);
	 break;
      }
   }

   close(fd);

   return ret;
}

// See ume.h for an indication of which entries of 'info' are inputs, which
// are outputs, and which are both.
int do_exec(const char *exe, struct exeinfo *info)
{
   info->interp_name = NULL;
   info->interp_args = NULL;

   return do_exec_inner(exe, info);
}

/*--------------------------------------------------------------------*/
/*--- end                                                    ume.c ---*/
/*--------------------------------------------------------------------*/