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/* $OpenBSD: testldt.c,v 1.5 2001/11/11 23:26:35 deraadt Exp $ */
/* $NetBSD: testldt.c,v 1.4 1995/04/20 22:42:38 cgd Exp $ */
#include <stdio.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <machine/segments.h>
extern int i386_get_ldt(int, union descriptor *, int);
extern int i386_set_ldt(int, union descriptor *, int);
int verbose = 0;
struct sigaction segv_act;
inline void set_fs(unsigned long val)
{
__asm__ __volatile__("mov %0,%%fs"::"r" ((unsigned short) val));
}
inline unsigned char get_fs_byte(const char * addr)
{
unsigned register char _v;
__asm__ ("movb %%fs:%1,%0":"=q" (_v):"m" (*addr));
return _v;
}
inline unsigned short get_cs(void)
{
unsigned register short _v;
__asm__ ("movw %%cs,%0"::"r" ((unsigned short) _v));
return _v;
}
int
check_desc(unsigned int desc)
{
desc = LSEL(desc, SEL_UPL);
set_fs(desc);
return(get_fs_byte((char *) 0));
}
void
gated_call()
{
printf("Called from call gate...");
__asm__ __volatile__("popl %ebp");
__asm__ __volatile__(".byte 0xcb");
}
struct segment_descriptor *
make_sd(unsigned base, unsigned limit, int type, int dpl, int seg32, int inpgs)
{
static struct segment_descriptor d;
d.sd_lolimit = limit & 0x0000ffff;
d.sd_lobase = base & 0x00ffffff;
d.sd_type = type & 0x01f;
d.sd_dpl = dpl & 0x3;
d.sd_p = 1;
d.sd_hilimit = (limit & 0x00ff0000) >> 16;
d.sd_xx = 0;
d.sd_def32 = seg32?1:0;
d.sd_gran = inpgs?1:0;
d.sd_hibase = (base & 0xff000000) >> 24;
return (&d);
}
struct gate_descriptor *
make_gd(unsigned offset, unsigned int sel, unsigned stkcpy, int type, int dpl)
{
static struct gate_descriptor d;
d.gd_looffset = offset & 0x0000ffff;
d.gd_selector = sel & 0xffff;
d.gd_stkcpy = stkcpy & 0x1ff;
d.gd_type = type & 0x1ff;
d.gd_dpl = dpl & 0x3;
d.gd_p = 1;
d.gd_hioffset = (offset & 0xffff0000) >> 16;
return(&d);
}
void
print_ldt(union descriptor *dp)
{
unsigned long base_addr, limit, offset, selector, stack_copy;
int type, dpl, i;
unsigned long *lp = (unsigned long *)dp;
/* First 32 bits of descriptor */
selector = base_addr = (*lp >> 16) & 0x0000FFFF;
offset = limit = *lp & 0x0000FFFF;
lp++;
/* First 32 bits of descriptor */
base_addr |= (*lp & 0xFF000000) | ((*lp << 16) & 0x00FF0000);
limit |= (*lp & 0x000F0000);
type = dp->sd.sd_type;
dpl = dp->sd.sd_dpl;
stack_copy = dp->gd.gd_stkcpy;
offset |= (*lp >> 16) & 0x0000FFFF;
if (type == SDT_SYS386CGT || type == SDT_SYS286CGT)
printf("LDT: Gate Off %08.8x, Sel %05.5x, Stkcpy %d DPL %d, Type %d\n",
offset, selector, stack_copy, dpl, type);
else
printf("LDT: Seg Base %08.8x, Limit %05.5x, DPL %d, Type %d\n",
base_addr, limit, dpl, type);
printf(" ");
if (*lp & 0x100)
printf("Accessed, ");
if (*lp & 8000)
printf("Present, ");
if (type != SDT_SYS386CGT && type != SDT_SYS286CGT) {
if (*lp & 0x100000)
printf("User, ");
if (*lp & 0x200000)
printf("X, ");
if (*lp & 0x400000)
printf("32, ");
else
printf("16, ");
if (*lp & 0x800000)
printf("page limit, ");
else
printf("byte limit, ");
}
printf("\n");
printf(" %08.8x %08.8x\n", *(lp), *(lp-1));
}
static void busfault(int signal, int code, struct sigcontext *sc)
{
fprintf(stderr, "\nbus fault - investigate.\n");
_exit(1);
}
static void usage(int status)
{
fprintf(stderr, "Usage: testldt [-v]\n");
exit(status);
}
#define MAX_USER_LDT 1024
main(int argc, char *argv[])
{
union descriptor ldt[MAX_USER_LDT];
int num, n, ch;
unsigned int cs = get_cs();
char *data;
struct segment_descriptor *sd;
struct gate_descriptor *gd;
segv_act.sa_handler = (sig_t) busfault;
if (sigaction(SIGBUS, &segv_act, NULL) < 0) {
perror("sigaction");
exit(1);
}
while ((ch = getopt(argc, argv, "v")) != -1) {
switch (ch) {
case 'v':
verbose++;
break;
default:
usage(1);
break;
}
}
printf("Testing i386_get_ldt...\n");
if ((num = i386_get_ldt(0, ldt, MAX_USER_LDT)) < 0) {
perror("get_ldt");
exit(2);
}
if (num == 0) {
fprintf(stderr, "ERROR: i386_get_ldt() return 0 default LDT entries.\n");
exit(1);
}
if (verbose) {
printf("Got %d (default) LDTs\n", num);
for (n=0; n < num; n++) {
printf("Entry %d: ", n);
print_ldt(&ldt[n]);
}
}
/*
* mmap a data area and assign an LDT to it
*/
printf("Testing i386_set_ldt...\n");
data = (void *) mmap( (char *)0x005f0000, 0x0fff,
PROT_EXEC | PROT_READ | PROT_WRITE,
MAP_FIXED | MAP_PRIVATE | MAP_ANON, -1, 0);
if (data == MAP_FAILED) {
perror("mmap");
exit(1);
}
if (verbose) printf("data address: %8.8x\n", data);
*data = 0x97;
/* Get the next free LDT and set it to the allocated data. */
sd = make_sd((unsigned)data, 4096, SDT_MEMRW, SEL_UPL, 0, 0);
if ((num = i386_set_ldt(6, (union descriptor *)sd, 1)) < 0) {
perror("set_ldt");
exit(1);
}
if (verbose) printf("setldt returned: %d\n", num);
if ((n = i386_get_ldt(num, ldt, 1)) < 0) {
perror("get_ldt");
exit(1);
}
if (verbose) {
printf("Entry %d: ", num);
print_ldt(&ldt[0]);
}
if (verbose) printf("Checking desc (should be 0x97): 0x%x\n", check_desc(num));
if (check_desc(num) != 0x97) {
fprintf(stderr, "ERROR: descriptor check failed: (should be 0x97): 0x%x\n", check_desc(num));
exit(1);
}
/*
* Test a Call Gate
*/
printf("Testing Call Gate...");
gd = make_gd((unsigned)gated_call, cs, 0, SDT_SYS386CGT, SEL_UPL);
if ((num = i386_set_ldt(5, (union descriptor *)gd, 1)) < 0) {
perror("set_ldt: call gate");
exit(1);
}
if (verbose) printf("setldt returned: %d\n", num);
if (verbose) printf("Call gate sel = 0x%x\n", LSEL(num, SEL_UPL));
if ((n = i386_get_ldt(num, ldt, 1)) < 0) {
perror("get_ldt");
exit(1);
}
if (verbose) printf("Entry %d: ", num);
if (verbose) print_ldt(&ldt[0]);
#if 0
err = setldt(5,
gated_call, /* Offset */
0x0001, /* This selector is for the executable segment descriptor. It
is the standard linux text descriptor. */
0x00008c00); /* Descriptor flags (you can't set all, the OS protects some) */
printf("setldt returned: %d\n", err);
#endif
__asm__ __volatile__(".byte 0x9a"); /* This is a call to a call gate. */
__asm__ __volatile__(".byte 0x00"); /* Value is ignored in a call gate but can be used. */
__asm__ __volatile__(".byte 0x00"); /* by the called procedure. */
__asm__ __volatile__(".byte 0x00");
__asm__ __volatile__(".byte 0x00");
__asm__ __volatile__(".byte 0x2f"); /* Selector 0x002f. This is index = 5 (the call gate), */
__asm__ __volatile__(".byte 0x00"); /* and a requestor priveledge level of 3. */
printf("Gated call returned\n");
exit (0);
}
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