ldt_keeper.c

/* applied some modification to make make our xine friend more happy */

/*
 * Modified for use with MPlayer, detailed CVS changelog at
 * http://www.mplayerhq.hu/cgi-bin/cvsweb.cgi/main/
 * $Id: ldt_keeper.c 11593 2005-06-28 18:02:01Z courmisch $
 */

#include "ldt_keeper.h"

#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
#ifdef __linux__
#include <asm/unistd.h>
#include <asm/ldt.h>
// 2.5.xx+ calls this user_desc:
#include <linux/version.h>
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,5,47)
#define modify_ldt_ldt_s user_desc
#endif
/* prototype it here, so we won't depend on kernel headers */
#ifdef  __cplusplus
extern "C" {
#endif

#if defined(__GLIBC__) &&  (__GLIBC__ < 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ == 0))
_syscall3( int, modify_ldt, int, func, void *, ptr, unsigned long, bytecount );
#else
int modify_ldt(int func, void *ptr, unsigned long bytecount);
#endif
#ifdef  __cplusplus
}
#endif
#else
#if defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__DragonFly__)
#include <machine/segments.h>
#include <machine/sysarch.h>
#endif

#ifdef __svr4__
#include <sys/segment.h>
#include <sys/sysi86.h>

/* solaris x86: add missing prototype for sysi86() */
#ifdef  __cplusplus
extern "C" {
#endif
int sysi86(int, void*);
#ifdef  __cplusplus
}
#endif

#ifndef NUMSYSLDTS             /* SunOS 2.5.1 does not define NUMSYSLDTS */
#define NUMSYSLDTS     6       /* Let's hope the SunOS 5.8 value is OK */
#endif

#define       TEB_SEL_IDX     NUMSYSLDTS
#endif

#define LDT_ENTRIES     8192
#define LDT_ENTRY_SIZE  8
#pragma pack(4)
struct modify_ldt_ldt_s {
        unsigned int  entry_number;
        unsigned long base_addr;
        unsigned int  limit;
        unsigned int  seg_32bit:1;
        unsigned int  contents:2;
        unsigned int  read_exec_only:1;
        unsigned int  limit_in_pages:1;
        unsigned int  seg_not_present:1;
        unsigned int  useable:1;
};

#define MODIFY_LDT_CONTENTS_DATA        0
#define MODIFY_LDT_CONTENTS_STACK       1
#define MODIFY_LDT_CONTENTS_CODE        2
#endif


/* user level (privilege level: 3) ldt (1<<2) segment selector */
#define       LDT_SEL(idx) ((idx) << 3 | 1 << 2 | 3)

/* i got this value from wine sources, it's the first free LDT entry */
#if defined(__FreeBSD__) && defined(LDT_AUTO_ALLOC)
#define       TEB_SEL_IDX     LDT_AUTO_ALLOC
#endif

#ifndef       TEB_SEL_IDX
#define       TEB_SEL_IDX     17
#endif

static unsigned int fs_ldt = TEB_SEL_IDX;


#ifdef __cplusplus
extern "C"
#endif
void Setup_FS_Segment(void)
{
    unsigned int ldt_desc = LDT_SEL(fs_ldt);

    __asm__ __volatile__(
        "movl %0,%%eax; movw %%ax, %%fs" : : "r" (ldt_desc)
        :"eax"
    );
}

/* we don't need this - use modify_ldt instead */
#if 0
#ifdef __linux__
/* XXX: why is this routine from libc redefined here? */
/* NOTE: the redefined version ignores the count param, count is hardcoded as 16 */
static int LDT_Modify( int func, struct modify_ldt_ldt_s *ptr,
                       unsigned long count )
{
    int res;
#ifdef __PIC__
    __asm__ __volatile__( "pushl %%ebx\n\t"
                          "movl %2,%%ebx\n\t"
                          "int $0x80\n\t"
                          "popl %%ebx"
                          : "=a" (res)
                          : "0" (__NR_modify_ldt),
                          "r" (func),
                          "c" (ptr),
                          "d"(16)//sizeof(*ptr) from kernel point of view
                          :"esi"     );
#else
    __asm__ __volatile__("int $0x80"
                         : "=a" (res)
                         : "0" (__NR_modify_ldt),
                         "b" (func),
                         "c" (ptr),
                         "d"(16)
                         :"esi");
#endif  /* __PIC__ */
    if (res >= 0) return res;
    errno = -res;
    return -1;
}
#endif
#endif

#if defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__DragonFly__)
static void LDT_EntryToBytes( unsigned long *buffer, const struct modify_ldt_ldt_s *content )
{
    *buffer++ = ((content->base_addr & 0x0000ffff) << 16) |
        (content->limit & 0x0ffff);
    *buffer = (content->base_addr & 0xff000000) |
        ((content->base_addr & 0x00ff0000)>>16) |
        (content->limit & 0xf0000) |
        (content->contents << 10) |
        ((content->read_exec_only == 0) << 9) |
        ((content->seg_32bit != 0) << 22) |
        ((content->limit_in_pages != 0) << 23) |
        0xf000;
}
#endif

void* fs_seg=0;

ldt_fs_t* Setup_LDT_Keeper(void)
{
    struct modify_ldt_ldt_s array;
    int ret;
    ldt_fs_t* ldt_fs = (ldt_fs_t*) malloc(sizeof(ldt_fs_t));

    if (!ldt_fs)
        return NULL;

    ldt_fs->fd = open("/dev/zero", O_RDWR);
    if(ldt_fs->fd<0){
        perror( "Cannot open /dev/zero for READ+WRITE. Check permissions! error: ");
        return NULL;
    }
    fs_seg=
    ldt_fs->fs_seg = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE, MAP_PRIVATE,
                          ldt_fs->fd, 0);
    if (ldt_fs->fs_seg == (void*)-1)
    {
        perror("ERROR: Couldn't allocate memory for fs segment");
        close(ldt_fs->fd);
        free(ldt_fs);
        return NULL;
    }
    *(void**)((char*)ldt_fs->fs_seg+0x18) = ldt_fs->fs_seg;
    memset(&array, 0, sizeof(array));
    array.base_addr=(int)ldt_fs->fs_seg;
    array.entry_number=TEB_SEL_IDX;
    array.limit=array.base_addr+getpagesize()-1;
    array.seg_32bit=1;
    array.read_exec_only=0;
    array.seg_not_present=0;
    array.contents=MODIFY_LDT_CONTENTS_DATA;
    array.limit_in_pages=0;
#ifdef __linux__
    //ret=LDT_Modify(0x1, &array, sizeof(struct modify_ldt_ldt_s));
    ret=modify_ldt(0x1, &array, sizeof(struct modify_ldt_ldt_s));
    if(ret<0)
    {
        perror("install_fs");
        printf("Couldn't install fs segment, expect segfault\n");
    }
#endif /*linux*/

#if defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__DragonFly__)
    {
        unsigned long d[2];

        LDT_EntryToBytes( d, &array );
#if defined(__FreeBSD__) && defined(LDT_AUTO_ALLOC)
        ret = i386_set_ldt(LDT_AUTO_ALLOC, (union descriptor *)d, 1);
        array.entry_number = ret;
        fs_ldt = ret;
#else
        ret = i386_set_ldt(array.entry_number, (union descriptor *)d, 1);
#endif
        if (ret < 0)
        {
            perror("install_fs");
            printf("Couldn't install fs segment, expect segfault\n");
            printf("Did you reconfigure the kernel with \"options USER_LDT\"?\n");
        }
    }
#endif  /* __NetBSD__ || __FreeBSD__ || __OpenBSD__ || __DragonFly__ */

#if defined(__svr4__)
    {
        struct ssd ssd;
        ssd.sel = LDT_SEL(TEB_SEL_IDX);
        ssd.bo = array.base_addr;
        ssd.ls = array.limit - array.base_addr;
        ssd.acc1 = ((array.read_exec_only == 0) << 1) |
            (array.contents << 2) |
            0xf0;   /* P(resent) | DPL3 | S */
        ssd.acc2 = 0x4;   /* byte limit, 32-bit segment */
        if (sysi86(SI86DSCR, &ssd) < 0) {
            perror("sysi86(SI86DSCR)");
            printf("Couldn't install fs segment, expect segfault\n");
        }
    }
#endif

    Setup_FS_Segment();

    ldt_fs->prev_struct = (char*)malloc(sizeof(char) * 8);
    *(void**)array.base_addr = ldt_fs->prev_struct;

    return ldt_fs;
}

void Restore_LDT_Keeper(ldt_fs_t* ldt_fs)
{
    if (ldt_fs == NULL || ldt_fs->fs_seg == 0)
        return;
    if (ldt_fs->prev_struct)
        free(ldt_fs->prev_struct);
    munmap((char*)ldt_fs->fs_seg, getpagesize());
    ldt_fs->fs_seg = 0;
    close(ldt_fs->fd);
    free(ldt_fs);
}

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