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#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <asm/uaccess.h>
#include <asm/fcntl.h>
#include <asm/unistd.h>
#include <asm/ia32_unistd.h>
#include <asm/msr.h>
#define THIS_DESCRIPTION "Dynamically get sys_call_table/ia32_sys_call_table in kernel module.\n\t\tI don't think there would be anyone who won't enable CONFIG_IA32_EMULATION these days.\n\t\tso you can add the unessary check if you really want to."
MODULE_DESCRIPTION( THIS_DESCRIPTION );
MODULE_AUTHOR("albcamus <[email protected]>");
MODULE_LICENSE("GPL");
/**
* TODO: if you want shut this up, comment the following line.
*/
#define BY_IDT_DEBUG
#ifdef BY_IDT_DEBUG
#define dbgprint(format,args...) \
printk("get_syscall: function:%s-L%d: "format, __FUNCTION__, __LINE__, ## args);
#else
#define dbgprint(format,args...) do {} while(0);
#endif
/**
* sys call table
*/
void ** my_ia32_syscall_table;
void ** my_syscall_table;
/**
* 10 bytes -- please refer to AMD64 Architecture Programmer's
* Manuals for more information.
*/
struct idtr {
unsigned short limit;
unsigned long base; //in 64bit mode, base address is 8 bytes
} __attribute__ ((packed));
/**
* in long mode -- 64bit mode and compatity mode,
* every IDT entry has a 16-byte size
*/
struct idt {
u16 offset_low;
u16 segment;
unsigned ist : 3, zero0 : 5, type : 5, dpl :2, p : 1;
u16 offset_middle;
u32 offset_high;
u32 zero1;
} __attribute__ ((packed));
/**
* Return the first appearence of NEEDLE in HAYSTACK. -- copied from PHRACK
* */
static void *memmem(const void *haystack, size_t haystack_len,
const void *needle, size_t needle_len)
{/*{{{*/
const char *begin;
const char *const last_possible
= (const char *) haystack + haystack_len - needle_len;
if (needle_len == 0)
/* The first occurrence of the empty string is deemed to occur at
the beginning of the string. */
return (void *) haystack;
/* Sanity check, otherwise the loop might search through the whole
memory. */
if (__builtin_expect(haystack_len < needle_len, 0))
return NULL;
for (begin = (const char *) haystack; begin <= last_possible;
++begin)
if (begin[0] == ((const char *) needle)[0]
&& !memcmp((const void *) &begin[1],
(const void *) ((const char *) needle + 1),
needle_len - 1))
return (void *) begin;
return NULL;
}/*}}}*/
/**
* Find the location of ia32_sys_call_table
*/
static unsigned long get_syscall_table_ia32(void)
{/*{{{*/
#define OFFSET_SYSCALL 100 /* from system_call/ia32_syscall, we'll read first 100 bytes */
struct idtr idtr;
struct idt idt;
unsigned long sys_call_off;
unsigned long retval;
char sc_asm[OFFSET_SYSCALL], *p;
/* well, let's read IDTR */
asm("sidt %0"
:"=m"(idtr)
: );
dbgprint("idtr base at %p\n", (void *)idtr.base);
/**
* Read in IDT for vector 0x80 (syscall)
*/
memcpy(&idt, (char *) idtr.base + 16 * 0x80, sizeof(idt));
sys_call_off = ( ( (unsigned long)idt.offset_high ) << 32 ) |
( ((idt.offset_middle << 16 ) | idt.offset_low) & 0x00000000ffffffff );
dbgprint("sys_call_off at %p\n", (void *)sys_call_off);
/* we have syscall routine address now, look for syscall table
dispatch (indirect call) */
memcpy(sc_asm, (void *)sys_call_off, OFFSET_SYSCALL);
/**
* ia32_call > ia32_tracesys > ia32_do_syscall > 'call *ia32_sys_call_table(,%rax,8)'
* Find callq *ia32_sys_call_table(,%rax,8)
*
* (gdb) disassemble ia32_syscall
* Dump of assembler code for function ia32_syscall:
* 0xffffffff81066b98 <ia32_syscall+0>: swapgs
* 0xffffffff81066b9b <ia32_syscall+3>: sti
* 0xffffffff81066b9c <ia32_syscall+4>: mov %eax,%eax
* 0xffffffff81066b9e <ia32_syscall+6>: push %rax
* 0xffffffff81066b9f <ia32_syscall+7>: cld
* 0xffffffff81066ba0 <ia32_syscall+8>: sub $0x48,%rsp
* 0xffffffff81066ba4 <ia32_syscall+12>: mov %rdi,0x40(%rsp)
* 0xffffffff81066ba9 <ia32_syscall+17>: mov %rsi,0x38(%rsp)
* 0xffffffff81066bae <ia32_syscall+22>: mov %rdx,0x30(%rsp)
* 0xffffffff81066bb3 <ia32_syscall+27>: mov %rcx,0x28(%rsp)
* 0xffffffff81066bb8 <ia32_syscall+32>: mov %rax,0x20(%rsp)
* 0xffffffff81066bbd <ia32_syscall+37>: mov %gs:0x10,%r10
* 0xffffffff81066bc6 <ia32_syscall+46>: sub $0x1fd8,%r10
* 0xffffffff81066bcd <ia32_syscall+53>: orl $0x2,0x14(%r10)
* 0xffffffff81066bd2 <ia32_syscall+58>: testl $0x181,0x10(%r10)
* 0xffffffff81066bda <ia32_syscall+66>: jne 0xffffffff81066c04 <ia32_tracesys>
* End of assembler dump.
* (gdb) disassemble ia32_tracesys
* Dump of assembler code for function ia32_tracesys:
* 0xffffffff81066c04 <ia32_tracesys+0>: sub $0x30,%rsp
* 0xffffffff81066c08 <ia32_tracesys+4>: mov %rbx,0x28(%rsp)
* 0xffffffff81066c0d <ia32_tracesys+9>: mov %rbp,0x20(%rsp)
* 0xffffffff81066c12 <ia32_tracesys+14>: mov %r12,0x18(%rsp)
* 0xffffffff81066c17 <ia32_tracesys+19>: mov %r13,0x10(%rsp)
* 0xffffffff81066c1c <ia32_tracesys+24>: mov %r14,0x8(%rsp)
* 0xffffffff81066c21 <ia32_tracesys+29>: mov %r15,(%rsp)
* 0xffffffff81066c25 <ia32_tracesys+33>: movq $0xffffffffffffffda,0x50(%rsp)
* 0xffffffff81066c2e <ia32_tracesys+42>: mov %rsp,%rdi
* 0xffffffff81066c31 <ia32_tracesys+45>: callq 0xffffffff81073a02 <syscall_trace_enter>
* 0xffffffff81066c36 <ia32_tracesys+50>: mov 0x30(%rsp),%r11
* 0xffffffff81066c3b <ia32_tracesys+55>: mov 0x38(%rsp),%r10
* 0xffffffff81066c40 <ia32_tracesys+60>: mov 0x40(%rsp),%r9
* 0xffffffff81066c45 <ia32_tracesys+65>: mov 0x48(%rsp),%r8
* 0xffffffff81066c4a <ia32_tracesys+70>: mov 0x58(%rsp),%rcx
* 0xffffffff81066c4f <ia32_tracesys+75>: mov 0x60(%rsp),%rdx
* 0xffffffff81066c54 <ia32_tracesys+80>: mov 0x68(%rsp),%rsi
* 0xffffffff81066c59 <ia32_tracesys+85>: mov 0x70(%rsp),%rdi
* 0xffffffff81066c5e <ia32_tracesys+90>: mov 0x78(%rsp),%rax
* 0xffffffff81066c63 <ia32_tracesys+95>: mov (%rsp),%r15
* 0xffffffff81066c67 <ia32_tracesys+99>: mov 0x8(%rsp),%r14
* 0xffffffff81066c6c <ia32_tracesys+104>: mov 0x10(%rsp),%r13
* 0xffffffff81066c71 <ia32_tracesys+109>: mov 0x18(%rsp),%r12
* 0xffffffff81066c76 <ia32_tracesys+114>: mov 0x20(%rsp),%rbp
* 0xffffffff81066c7b <ia32_tracesys+119>: mov 0x28(%rsp),%rbx
* 0xffffffff81066c80 <ia32_tracesys+124>: add $0x30,%rsp
* 0xffffffff81066c84 <ia32_tracesys+128>: jmpq 0xffffffff81066bdc <ia32_do_syscall>
* End of assembler dump.
* (gdb) disassemble ia32_do_syscall
* Dump of assembler code for function ia32_do_syscall:
* 0xffffffff81066bdc <ia32_do_syscall+0>: cmp $0x13d,%eax
* 0xffffffff81066be1 <ia32_do_syscall+5>: ja 0xffffffff81066c89 <ia32_badsys>
* 0xffffffff81066be7 <ia32_do_syscall+11>: mov %edi,%r8d
* 0xffffffff81066bea <ia32_do_syscall+14>: mov %ebp,%r9d
* 0xffffffff81066bed <ia32_do_syscall+17>: xchg %ecx,%esi
* 0xffffffff81066bef <ia32_do_syscall+19>: mov %ebx,%edi
* 0xffffffff81066bf1 <ia32_do_syscall+21>: mov %edx,%edx
* 0xffffffff81066bf3 <ia32_do_syscall+23>: callq *0xffffffff812e7c70(,%rax,8)
* End of assembler dump.
* (gdb) x/xw ia32_do_syscall+23
* 0xffffffff81066bf3 <ia32_do_syscall+23>: 0x70c514ff
* (gdb)
*
*/
p = (char *) memmem(sc_asm, OFFSET_SYSCALL, "\xff\x14\xc5", 3);
if (p == NULL) {
printk("opcode not found, meats that we cannot find sys_call_table.\n");
return 0;
}
retval = *(unsigned long *) (p + 3);
return retval;
#undef OFFSET_SYSCALL
}/*}}}*/
/**
* Find the location of long-mode sys_call_table
*/
static unsigned long get_syscall_table_long(void)
{/*{{{*/
#define OFFSET_SYSCALL 150
unsigned long syscall_long, retval;
char sc_asm[OFFSET_SYSCALL];
rdmsrl(MSR_LSTAR, syscall_long);
dbgprint("long mode: system_call is at %p\n", (void *)syscall_long);
memcpy(sc_asm, (char *)syscall_long, OFFSET_SYSCALL);
/**
* Find callq *sys_call_table(,%rax,8)
* -------------------------------------
* (gdb) disassemble system_call
* Dump of assembler code for function system_call:
* 0xffffffff81063750 <system_call+0>: swapgs
* 0xffffffff81063753 <system_call+3>: mov %rsp,%gs:0x18
* 0xffffffff8106375c <system_call+12>: mov %gs:0x10,%rsp
* 0xffffffff81063765 <system_call+21>: sti
* 0xffffffff81063766 <system_call+22>: sub $0x50,%rsp
* 0xffffffff8106376a <system_call+26>: mov %rdi,0x40(%rsp)
* 0xffffffff8106376f <system_call+31>: mov %rsi,0x38(%rsp)
* 0xffffffff81063774 <system_call+36>: mov %rdx,0x30(%rsp)
* 0xffffffff81063779 <system_call+41>: mov %rax,0x20(%rsp)
* 0xffffffff8106377e <system_call+46>: mov %r8,0x18(%rsp)
* 0xffffffff81063783 <system_call+51>: mov %r9,0x10(%rsp)
* 0xffffffff81063788 <system_call+56>: mov %r10,0x8(%rsp)
* 0xffffffff8106378d <system_call+61>: mov %r11,(%rsp)
* 0xffffffff81063791 <system_call+65>: mov %rax,0x48(%rsp)
* 0xffffffff81063796 <system_call+70>: mov %rcx,0x50(%rsp)
* 0xffffffff8106379b <system_call+75>: mov %gs:0x10,%rcx
* 0xffffffff810637a4 <system_call+84>: sub $0x1fd8,%rcx
* 0xffffffff810637ab <system_call+91>: testl $0x181,0x10(%rcx)
* 0xffffffff810637b2 <system_call+98>: jne 0xffffffff81063889 <tracesys>
* 0xffffffff810637b8 <system_call+104>: cmp $0x117,%rax
* 0xffffffff810637be <system_call+110>: ja 0xffffffff8106387b <badsys>
* 0xffffffff810637c4 <system_call+116>: mov %r10,%rcx
* 0xffffffff810637c7 <system_call+119>: callq *0xffffffff812e6d60(,%rax,8)
* 0xffffffff810637ce <system_call+126>: mov %rax,0x20(%rsp)
* End of assembler dump.
* (gdb) x/xw system_call+119
* 0xffffffff810637c7 <system_call+119>: 0x60c514ff
* (gdb)
*/
retval = (unsigned long) memmem(sc_asm, OFFSET_SYSCALL, "\xff\x14\xc5", 3);
if ( retval != 0 ) {
dbgprint("long mode : sys_call_table is at %p\n",
(void *) (* (unsigned long *)(retval+3)) ) ;
retval = (unsigned long) ( * (unsigned long *)(retval+3) );
} else {
printk("long mode : memmem found nothing, returning NULL:( \n");
retval = 0;
}
#undef OFFSET_SYSCALL
return retval;
}/*}}}*/
static int get_syscall_init_module(void)
{/*{{{*/
printk(KERN_DEBUG "get_syscall: Hi, you fucking linux!\n");
my_ia32_syscall_table = (void **) get_syscall_table_ia32();
if (my_ia32_syscall_table == 0)
return -1;
my_syscall_table = (void **) get_syscall_table_long();
if (my_syscall_table == 0)
return -1;
dbgprint("ia32_sys_call_table address : %p\n", (void *) my_ia32_syscall_table);
dbgprint("long mode : sys_call_table address : %p\n", (void *) my_syscall_table);
#define REPLACE_IA32(x) o_sys_##x = my_ia32_syscall_table[__NR_ia32_##x];\
my_ia32_syscall_table[__NR_ia32_##x] = my_sys_##x
#define GET_OLD_IA32_SYSCALL_ADDR(x) my_ia32_syscall_table[__NR_ia32_##x]
// dbgprint("sys_read at %p, my_read at %p\n", (void *)GET_OLD_IA32_SYSCALL_ADDR(read), (void *)my_sys_read);
// REPLACE_IA32(read);
#undef REPLACE_IA32
return 0;
}/*}}}*/
static void get_syscall_exit_module(void)
{/*{{{*/
printk(KERN_DEBUG "get_syscall: bye, you fucking linux!\n");
#define RESTORE_IA32(x) my_ia32_syscall_table[__NR_ia32_##x] = o_sys_##x
// RESTORE_IA32(read);
#undef RESTORE_IA32
}/*}}}*/
module_init(get_syscall_init_module);
module_exit(get_syscall_exit_module);
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