/*
* Copyright (C) 2004 aCaB <acab@clamav.net>
*
* 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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
** upxdec.c
**
** 05/05/2k4 - 1st attempt
** 08/05/2k4 - Now works as a charm :D
** 09/05/2k4 - Moved code outta main(), got rid of globals for thread safety, added bound checking, minor cleaning
** 04/06/2k4 - Now we handle 2B, 2D and 2E :D
** 28/08/2k4 - PE rebuild for nested packers
** 12/12/2k4 - Improved PE rebuild code and added some debug info on failure
*/
/*
** This code unpacks a dumped UPX1 section to a file.
** It was written reversing the loader found on some Win32 UPX compressed trojans; while porting
** it to C i've kinda followed the asm flow so it will probably be a bit hard to read.
** This code DOES NOT revert the uncompressed section to its original state as no E8/E9 fixup and
** of cause no IAT rebuild are performed.
**
** The Win32 asm unpacker is really a little programming jewel, pretty damn rare in these days of
** bloatness. My gratitude to whoever wrote it.
*/
#if HAVE_CONFIG_H
#include "clamav-config.h"
#endif
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <string.h>
#include "cltypes.h"
#include "others.h"
#define HEADERS "\
\x4D\x5A\x90\x00\x02\x00\x00\x00\x04\x00\x0F\x00\xFF\xFF\x00\x00\
\xB0\x00\x00\x00\x00\x00\x00\x00\x40\x00\x1A\x00\x00\x00\x00\x00\
\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\
\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xD0\x00\x00\x00\
\x0E\x1F\xB4\x09\xBA\x0D\x00\xCD\x21\xB4\x4C\xCD\x21\x54\x68\x69\
\x73\x20\x66\x69\x6C\x65\x20\x77\x61\x73\x20\x63\x72\x65\x61\x74\
\x65\x64\x20\x62\x79\x20\x43\x6C\x61\x6D\x41\x56\x20\x66\x6F\x72\
\x20\x69\x6E\x74\x65\x72\x6E\x61\x6C\x20\x75\x73\x65\x20\x61\x6E\
\x64\x20\x73\x68\x6F\x75\x6C\x64\x20\x6E\x6F\x74\x20\x62\x65\x20\
\x72\x75\x6E\x2E\x0D\x0A\x43\x6C\x61\x6D\x41\x56\x20\x2D\x20\x41\
\x20\x47\x50\x4C\x20\x76\x69\x72\x75\x73\x20\x73\x63\x61\x6E\x6E\
\x65\x72\x20\x2D\x20\x68\x74\x74\x70\x3A\x2F\x2F\x77\x77\x77\x2E\
\x63\x6C\x61\x6D\x61\x76\x2E\x6E\x65\x74\x0D\x0A\x24\x00\x00\x00\
"
/* PE from UPX */
int pefromupx (char *src, char *dst, uint32_t *dsize, uint32_t ep, uint32_t upx0, uint32_t upx1, uint32_t magic)
{
char *imports, *sections, *pehdr, *newbuf;
int sectcnt, upd=1;
uint32_t realstuffsz;
uint32_t foffset=0xd0+0xf8;
if((dst == NULL) || (src == NULL))
return 0;
imports = dst + cli_readint32(src + ep - upx1 + magic);
realstuffsz = imports-dst;
if (realstuffsz >= *dsize ) {
cli_dbgmsg("UPX: wrong realstuff size - giving up rebuild\n");
return 0;
}
pehdr = imports;
while (CLI_ISCONTAINED(dst, *dsize, pehdr, 8) && cli_readint32(pehdr)) {
pehdr+=8;
while(CLI_ISCONTAINED(dst, *dsize, pehdr, 2) && *pehdr) {
pehdr++;
while (CLI_ISCONTAINED(dst, *dsize, pehdr, 2) && *pehdr)
pehdr++;
pehdr++;
}
pehdr++;
}
pehdr+=4;
if (!CLI_ISCONTAINED(dst, *dsize, pehdr, 0xf8)) {
cli_dbgmsg("UPX: sections out of bounds - giving up rebuild\n");
return 0;
}
if ( cli_readint32(pehdr) != 0x4550 ) {
cli_dbgmsg("UPX: No magic for PE - giving up rebuild\n");
return 0;
}
if (! cli_readint32(pehdr+0x38)) {
cli_dbgmsg("UPX: Cant align to a NULL bound - giving up rebuild\n");
return 0;
}
sections = pehdr+0xf8;
if ( ! (sectcnt = (unsigned char)pehdr[6]+256*(unsigned char)pehdr[7])) {
cli_dbgmsg("UPX: No sections? - giving up rebuild\n");
return 0;
}
foffset+=0x28*sectcnt;
if (!CLI_ISCONTAINED(dst, *dsize, sections, 0x28*sectcnt)) {
cli_dbgmsg("UPX: Not enough space for all sects - giving up rebuild\n");
return 0;
}
for (upd = 0; upd <sectcnt ; upd++) {
uint32_t vsize=cli_readint32(sections+8)-1;
uint32_t rsize=cli_readint32(sections+16);
uint32_t urva=cli_readint32(sections+12);
vsize=(((vsize/0x1000)+1)*0x1000); /* FIXME: get bounds from header */
/* Within bounds ? */
if (!CLI_ISCONTAINED(upx0, realstuffsz, urva, vsize)) {
cli_dbgmsg("UPX: Sect %d out of bounds - giving up rebuild\n", upd);
return 0;
}
/* Rsize -gt Vsize ? */
if ( rsize > vsize ) {
cli_dbgmsg("UPX: Raw size for sect %d is greater than virtual (%x / %x) - giving up rebuild\n", upd, rsize, vsize);
return 0;
}
/* Am i been fooled? There are better ways ;) */
if ( rsize+4 < vsize && cli_readint32(dst+urva-upx0+rsize) ) {
cli_dbgmsg("UPX: Am i been fooled? - giving up rebuild\n", upd);
return 0;
}
cli_writeint32(sections+8, vsize);
cli_writeint32(sections+20, foffset);
foffset+=rsize;
if (foffset > *dsize) {
cli_dbgmsg("UPX: wrong raw size - giving up rebuild\n");
return 0;
}
sections+=0x28;
}
cli_writeint32(pehdr+8, 0x4d414c43);
if (!(newbuf = (char *) cli_malloc(foffset))) {
cli_dbgmsg("UPX: malloc failed - giving up rebuild\n", upd);
return 0;
}
memcpy(newbuf, HEADERS, 0xd0);
memcpy(newbuf+0xd0, pehdr,0xf8+0x28*sectcnt);
sections = pehdr+0xf8;
for (upd = 0; upd <sectcnt ; upd++) {
memcpy(newbuf+cli_readint32(sections+20), dst+cli_readint32(sections+12)-upx0, cli_readint32(sections+16));
sections+=0x28;
}
/* CBA restoring the imports they'll look different from the originals anyway... */
/* ...and yeap i miss the icon too :P */
memcpy(dst, newbuf, foffset);
*dsize = foffset;
free(newbuf);
cli_dbgmsg("UPX: PE structure rebuilt from compressed file\n");
return 1;
}
/* [doubleebx] */
static int doubleebx(char *src, int32_t *myebx, int *scur, int ssize)
{
int32_t oldebx = *myebx;
*myebx*=2;
if ( !(oldebx & 0x7fffffff)) {
if (! CLI_ISCONTAINED(src, ssize, src+*scur, 4))
return -1;
oldebx = cli_readint32(src+*scur);
*myebx = oldebx*2+1;
*scur+=4;
}
return (oldebx>>31)&1;
}
/* [inflate] */
int upx_inflate2b(char *src, uint32_t ssize, char *dst, uint32_t *dsize, uint32_t upx0, uint32_t upx1, uint32_t ep)
{
int32_t backbytes, unp_offset = -1, myebx = 0;
int scur=0, dcur=0, i, backsize, oob;
while (1) {
while ((oob = doubleebx(src, &myebx, &scur, ssize)) == 1) {
if (scur<0 || scur>=ssize || dcur<0 || dcur>=*dsize)
return -1;
dst[dcur++] = src[scur++];
}
if ( oob == -1 )
return -1;
backbytes = 1;
while (1) {
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
backbytes = backbytes*2+oob;
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
if (oob)
break;
}
backsize = 0;
backbytes-=3;
if ( backbytes >= 0 ) {
if (scur<0 || scur>=ssize)
return -1;
backbytes<<=8;
backbytes+=(unsigned char)(src[scur++]);
backbytes^=0xffffffff;
if (!backbytes)
break;
unp_offset = backbytes;
}
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1)
return -1;
backsize = oob;
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1)
return -1;
backsize = backsize*2 + oob;
if (!backsize) {
backsize++;
do {
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1)
return -1;
backsize = backsize*2 + oob;
} while ((oob = doubleebx(src, &myebx, &scur, ssize)) == 0);
if ( oob == -1 )
return -1;
backsize+=2;
}
if ( (uint32_t)unp_offset < 0xfffff300 )
backsize++;
backsize++;
for (i = 0; i < backsize; i++) {
if (dcur+i<0 || dcur+i>=*dsize || dcur+unp_offset+i<0 || dcur+unp_offset+i>=*dsize)
return -1;
dst[dcur + i] = dst[dcur + unp_offset + i];
}
dcur+=backsize;
}
if ( ep - upx1 + 0x108 <= ssize-5 && /* Wondering how we got so far?! */
src[ep - upx1 + 0x106] == '\x8d' && /* lea edi, ... */
src[ep - upx1 + 0x107] == '\xbe' ) /* ... [esi + offset] */
return pefromupx (src, dst, dsize, ep, upx0, upx1, 0x108);
cli_dbgmsg("UPX: bad magic for 2b\n");
return 0;
}
int upx_inflate2d(char *src, uint32_t ssize, char *dst, uint32_t *dsize, uint32_t upx0, uint32_t upx1, uint32_t ep)
{
int32_t backbytes, unp_offset = -1, myebx = 0;
int scur=0, dcur=0, i, backsize, oob;
while (1) {
while ( (oob = doubleebx(src, &myebx, &scur, ssize)) == 1) {
if (scur<0 || scur>=ssize || dcur<0 || dcur>=*dsize)
return -1;
dst[dcur++] = src[scur++];
}
if ( oob == -1 )
return -1;
backbytes = 1;
while (1) {
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
backbytes = backbytes*2+oob;
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
if (oob)
break;
backbytes--;
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
backbytes=backbytes*2+oob;
}
backsize = 0;
backbytes-=3;
if ( backbytes >= 0 ) {
if (scur<0 || scur>=ssize)
return -1;
backbytes<<=8;
backbytes+=(unsigned char)(src[scur++]);
backbytes^=0xffffffff;
if (!backbytes)
break;
backsize = backbytes & 1;
backbytes>>=1;
unp_offset = backbytes;
}
else {
if ( (backsize = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
}
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
backsize = backsize*2 + oob;
if (!backsize) {
backsize++;
do {
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
backsize = backsize*2 + oob;
} while ( (oob = doubleebx(src, &myebx, &scur, ssize)) == 0);
if ( oob == -1 )
return -1;
backsize+=2;
}
if ( (uint32_t)unp_offset < 0xfffffb00 )
backsize++;
backsize++;
for (i = 0; i < backsize; i++) {
if (dcur+i<0 || dcur+i>=*dsize || dcur+unp_offset+i<0 || dcur+unp_offset+i>=*dsize)
return -1;
dst[dcur + i] = dst[dcur + unp_offset + i];
}
dcur+=backsize;
}
if ( ep - upx1 + 0x124 <= ssize-5 ) { /* Wondering how we got so far?! */
if ( src[ep - upx1 + 0x11a] == '\x8d' && src[ep - upx1 + 0x11b] == '\xbe' )
return pefromupx (src, dst, dsize, ep, upx0, upx1, 0x11c);
if ( src[ep - upx1 + 0x122] == '\x8d' && src[ep - upx1 + 0x123] == '\xbe' )
return pefromupx (src, dst, dsize, ep, upx0, upx1, 0x124);
}
cli_dbgmsg("UPX: bad magic for 2d\n");
return 0;
}
int upx_inflate2e(char *src, uint32_t ssize, char *dst, uint32_t *dsize, uint32_t upx0, uint32_t upx1, uint32_t ep)
{
int32_t backbytes, unp_offset = -1, myebx = 0;
int scur=0, dcur=0, i, backsize, oob;
for(;;) {
while ( (oob = doubleebx(src, &myebx, &scur, ssize)) ) {
if (oob == -1)
return -1;
if (scur<0 || scur>=ssize || dcur<0 || dcur>=*dsize)
return -1;
dst[dcur++] = src[scur++];
}
backbytes = 1;
for(;;) {
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
backbytes = backbytes*2+oob;
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
if ( oob )
break;
backbytes--;
if ( (oob = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
backbytes=backbytes*2+oob;
}
backsize = 0;
backbytes-=3;
if ( backbytes >= 0 ) {
if (scur<0 || scur>=ssize)
return -1;
backbytes<<=8;
backbytes+=(unsigned char)(src[scur++]);
backbytes^=0xffffffff;
if (!backbytes)
break;
backsize = backbytes & 1; /* Using backsize to carry on the shifted out bit (UPX uses CF) */
backbytes>>=1;
unp_offset = backbytes;
}
else {
if ( (backsize = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
} /* Using backsize to carry on the doubleebx result (UPX uses CF) */
if (backsize) { /* i.e. IF ( last sar shifted out 1 bit || last doubleebx()==1 ) */
if ( (backsize = doubleebx(src, &myebx, &scur, ssize)) == -1 )
return -1;
}
else {
backsize = 1;
if ((oob = doubleebx(src, &myebx, &scur, ssize)) == -1)
return -1;
if (oob) {
if ((oob = doubleebx(src, &myebx, &scur, ssize)) == -1)
return -1;
backsize = 2 + oob;
}
else {
do {
if ((oob = doubleebx(src, &myebx, &scur, ssize)) == -1)
return -1;
backsize = backsize * 2 + oob;
} while ((oob = doubleebx(src, &myebx, &scur, ssize)) == 0);
if (oob == -1)
return -1;
backsize+=2;
}
}
if ( (uint32_t)unp_offset < 0xfffffb00 )
backsize++;
backsize+=2;
for (i = 0; i < backsize; i++) {
if (dcur+i<0 || dcur+i>=*dsize || dcur+unp_offset+i<0 || dcur+unp_offset+i>=*dsize)
return -1;
dst[dcur + i] = dst[dcur + unp_offset + i];
}
dcur+=backsize;
}
if ( ep - upx1 + 0x130 <= ssize-5 ) { /* Wondering how we got so far?! */
if ( src[ep - upx1 + 0x126] == '\x8d' && src[ep - upx1 + 0x127] == '\xbe' )
return pefromupx (src, dst, dsize, ep, upx0, upx1, 0x128);
if ( src[ep - upx1 + 0x12e] == '\x8d' && src[ep - upx1 + 0x12f] == '\xbe' )
return pefromupx (src, dst, dsize, ep, upx0, upx1, 0x130);
}
cli_dbgmsg("UPX: bad magic for 2e\n");
return 0;
}