bool drakvuf_get_thread_previous_mode( drakvuf_t drakvuf, addr_t kthread, privilege_mode_t *previous_mode )
{
if ( kthread )
{
*previous_mode = 0 ;
if ( vmi_read_8_va( drakvuf->vmi, kthread + drakvuf->offsets[ KTHREAD_PREVIOUSMODE ], 0,
(uint8_t *)previous_mode ) == VMI_SUCCESS )
{
if ( ( *previous_mode == KERNEL_MODE ) || ( *previous_mode == USER_MODE ) )
return true ;
}
}
return false ;
}
int main (int argc, char **argv)
{
// local variables
vmi_instance_t vmi;
int ret_val = 0; // return code for after goto
struct sigaction signal_action;
// process list vars
vmi_pid_t pid = 0;
char *procname = NULL;
addr_t list_head = 0;
addr_t next_list_entry = 0;
addr_t current_process = 0;
addr_t tmp_next = 0;
status_t status;
// breakpoint vars
char* *sym;
uint16_t *off;
vmi_pid_t *bpid;
addr_t *add;
uint8_t *byt;
addr_t lib_map_addr = 0;
addr_t BN_rand_addr = 0;
int bnrand_jump_offset = 0;
addr_t bnrand_addr = 0;
// this is the VM or file that we are looking at
if (argc < 2) {
printf("Usage: %s <vmname>\n", argv[0]);
return 1;
}
char *name = argv[1];
////////////////////
// Initialization //
////////////////////
// initialize the libvmi library
printf("Initializing libvmi for VM \"%s\"\n", name);
if (vmi_init(&vmi, VMI_XEN|VMI_INIT_COMPLETE|VMI_INIT_EVENTS, name) == VMI_FAILURE) {
printf("Failed to init LibVMI library.\n");
ret_val = 2;
goto error_exit;
}
// verify OS is Linux
printf("Verifying the VM is running Linux...");
// TODO: verify that the VM is running a *supported* Linux kernel
// if kernel is not one we recognize, don't run because we'll be mucking around in memory we don't understand
if (VMI_OS_LINUX != vmi_get_ostype(vmi)) { // this only checks if /etc/libvmi.conf says it's "Linux"
printf("\nVM is running %s, exiting...\n", vmi_get_ostype(vmi));
ret_val = 3;
goto error_exit;
}
printf(" Yup. Good to go.\n");
// pause the vm for consistent memory access
printf("Pausing the VM\n");
if (vmi_pause_vm(vmi) != VMI_SUCCESS) {
printf("Failed to pause VM\n");
ret_val = 4;
goto error_exit; // don't return directly, do cleanup first
}
tasks_offset = vmi_get_offset(vmi, "linux_tasks");
name_offset = vmi_get_offset(vmi, "linux_name");
pid_offset = vmi_get_offset(vmi, "linux_pid");
mm_offset = vmi_get_offset(vmi, "linux_mm");
// hardcoded because config_parser doesn't support dynamic config vars
mmap_offset = 0x0;
vm_area_file_offset = 0xa0;
vm_area_next_offset = 0x10;
vm_area_start_offset = 0x0;
file_path_offset = 0x10;
dentry_offset = 0x8;
iname_offset = 0x38;
//mmap_offset = vmi_get_offset(vmi, "linux_mmap");
//vm_area_file_offset = vmi_get_offset(vmi, "linux_vm_file");
//vm_area_next_offset = vmi_get_offset(vmi, "linux_vm_next");
//vm_area_start_offset = vmi_get_offset(vmi, "linux_vm_start");
//file_path_offset = vmi_get_offset(vmi, "linux_f_path");
//dentry_offset = vmi_get_offset(vmi, "linux_dentry");
//iname_offset = vmi_get_offset(vmi, "linux_d_iname");
if (0 == tasks_offset) {
printf("Failed to find tasks_offset\n");
goto error_exit;
}
if (0 == pid_offset) {
printf("Failed to find pid_offset\n");
goto error_exit;
}
if (0 == name_offset) {
printf("Failed to find name_offset\n");
goto error_exit;
}
if (0 == mm_offset) {
printf("Failed to find mm_offset\n");
goto error_exit;
}
//if (0 == mmap_offset) {
// printf("Failed to find mmap_offset\n");
// goto error_exit;
//}
//if (0 == vm_area_file_offset) {
// printf("Failed to find vm_area_file_offset\n");
// goto error_exit;
//}
//if (0 == vm_area_next_offset) {
// printf("Failed to find vm_area_next_offset\n");
// goto error_exit;
//}
//if (0 == vm_area_start_offset) {
// printf("Failed to find vm_area_start_offset\n");
// goto error_exit;
//}
//if (0 == file_path_offset) {
// printf("Failed to find file_path_offset\n");
// goto error_exit;
//}
//if (0 == dentry_offset) {
// printf("Failed to find dentry_offset\n");
// goto error_exit;
//}
//if (0 == iname_offset) {
// printf("Failed to find iname_offset\n");
// goto error_exit;
//}
// Set up breakpoints
breakpoints = (breakpoint_t*)calloc(MAX_BREAKPOINTS, sizeof(breakpoint_t)); // allocate space for each breakpoint, zero memory
//add_breakpoint("extract_entropy_user", 155, 0, 0xe8, before_extract_buf);
//add_breakpoint("extract_entropy_user", 160, 0, 0x83, after_extract_buf);
// new breakpoints created below
//////////////////////////
// Find apache2 process //
//////////////////////////
// find pid of apache2 processes
// for each process, read symbol table and find BN_rand function
// at offset +13 bytes from BN_rand, we find an offset from the instruction at BN_rand+17 (probably around -700 bytes)
// +570 bytes from the offset above, we find the instruction at which we want a breakpoint
// so, breakpoint at BN_rand+17+[BN_rand+13]+570
// then, at callback, read r13 for address of buffer, overwrite with TODO bytes
// find pid of apache2 processes
list_head = vmi_translate_ksym2v(vmi, "init_task") + tasks_offset; // find init_task struct and move to first linked list entry
next_list_entry = list_head; // iterator
do {
current_process = next_list_entry - tasks_offset; // subtract tasks_offset back off to get to head of struct
vmi_read_32_va(vmi, current_process + pid_offset, 0, (uint32_t*)&pid); // get pid of this process
procname = vmi_read_str_va(vmi, current_process + name_offset, 0); // get process name of this process
if (strncmp(procname,"apache2",sizeof("apache2")) == 0) {
printf("Finding library address in %s [pid %d]\n",procname,pid);
lib_map_addr = walk_vmmap_for_lib(vmi, current_process, "libcrypto.so.1.0.2");
if (lib_map_addr == 0) { // if failed to find lib
printf("Failed to find library in %s\n",procname);
ret_val = 9;
goto error_exit;
}
printf("Found library address: 0x%llx\n", lib_map_addr);
// for each process, read symbol table and find BN_rand function
BN_rand_addr = lib_map_addr + 0xd5a50; // static offset for BN_rand function
// at offset +13 bytes from BN_rand, we find an offset from the instruction at BN_rand+17 (probably around -700 bytes)
vmi_read_32_va(vmi, BN_rand_addr+13, pid, &bnrand_jump_offset); // get jump offset to bnrand function
//printf("jump offset: %d\n",bnrand_jump_offset);
bnrand_addr = BN_rand_addr+17+bnrand_jump_offset; // get address of bnrand function
//printf("bnrand: 0x%llx\n", bnrand_addr);
// +570 bytes from the offset above, we find the instruction at which we want a breakpoint
add_breakpoint_addr(bnrand_addr + 570, pid, 0x31, bnrand_callback);
//printf("Added breakpoint at 0x%llx\n",bnrand_addr+570);
}
status = vmi_read_addr_va(vmi, next_list_entry, 0, &next_list_entry); // follow linked-list->next to next element
if (status == VMI_FAILURE) {
printf("Failed to read next pointer in loop at %"PRIx64"\n", next_list_entry);
goto error_exit;
}
} while(next_list_entry != list_head);
for (int i = 0; i < num_breakpoints; i++) { // iterate over breakpoints and find the right addresses for them
////////////////////////////////////////////
// Find memory location to put breakpoint //
////////////////////////////////////////////
// assign short names (note: modifying these modifies the breakpoint struct)
sym = &breakpoints[i].symbol;
off = &breakpoints[i].offset;
bpid = &breakpoints[i].pid;
add = &breakpoints[i].addr;
byt = &breakpoints[i].inst_byte; // remember that if this is not set above, it should be zeroed from calloc
if (breakpoints[i].addr == 0) { // if don't have address, find symbol
// find address to break on
printf("Accessing System Map for %s symbol\n", *sym);
*add = vmi_translate_ksym2v(vmi, *sym) + *off;
printf("%s + %u is at 0x%llx\n", *sym, *off, *add);
}
// either verify the byte there is correct, or record which byte is there for later replacing
if (*byt == 0) { // if this byte was not set, we need to get it
vmi_read_8_va(vmi, *add, *bpid, byt); // read it directly into byt
printf("[pid %d] Saving byte at address 0x%llx: %x\n", *bpid, *add, *byt);
} else { // if the byte was set, verify that it's currently set to that value
uint8_t temp_byte = 0;
vmi_read_8_va(vmi, *add, *bpid, &temp_byte); // read it temporarily
printf("[pid %d] Checking byte at address 0x%llx is set to %x: %x\n", *bpid, *add, *byt, temp_byte);
if (*byt != temp_byte) { // uh oh, we have an error
ret_val = 8;
goto error_exit;
}
}
} // end first for loop after breakpoints are constructed properly
///////////////////
// Main gameplan //
// //
// https://groups.google.com/forum/#!topic/vmitools/jNGxM0LBEDM
// Based on the google groups discussion above (which I wish I found earlier, meh), it looks like the way people trap on instructions is to:
// 1) actually *modify* the memory to have the 0xcc (interrupt 3, aka breakpoint) instruction in place of the instruction it would have executed
// 2) register an event on receiving the INT3 signal and receive the callback
// 3) at the end of the callback, fix the memory to its original instruction,
// 4) single-step one instruction forward, executing the one instruction, then getting another callback
// 5) replace the previous instruction with to 0xcc, "resetting" the breakpoint, then clearing the event and continuing
// //
///////////////////
for (int i = 0; i < num_breakpoints; i++) { // iterate over breakpoints and insert them all
// assign short names (note: modifying these modifies the breakpoint struct)
add = &breakpoints[i].addr;
bpid = &breakpoints[i].pid;
byt = &breakpoints[i].inst_byte;
// Step 1: modify memory in the VM with an INT3 instruction (0xcc)
printf("[pid %d] Setting breakpoint at address 0x%llx.\n", *bpid, *add);
uint8_t int3 = INT3_INST; // create temporary variable because we can't use an address to a static #defined int
if (VMI_SUCCESS != vmi_write_8_va(vmi, *add, *bpid, &int3)) {
printf("[pid %d] Couldn't write INT3 instruction to memory... exiting.\n", *bpid);
ret_val = 5;
goto error_exit;
}
// debug: check memory is now an INT3 instruction
uint8_t temp_byte = 0;
vmi_read_8_va(vmi, *add, 0, &temp_byte);
printf("[pid %d] This should be an INT3 instruction (0xcc): 0x%x\n", *bpid, temp_byte);
} // end second for loop after breakpoints are all inserted and callback is registered
// Step 2: register an event on receiving INT3 signal
printf("Creating event for callback when breakpoint is reached.\n");
memset(&rng_event, 0, sizeof(vmi_event_t)); // clear rng_event so we can set everything fresh
rng_event.type = VMI_EVENT_INTERRUPT; // interrupt event -- trigger when interrupt occurs
rng_event.interrupt_event.intr = INT3; // trigger on INT3 instruction
rng_event.interrupt_event.reinject = 0; // swallow interrupt silently without passing it on to guest
rng_event.callback = rng_int3_event_callback; // reference to our callback function
printf("Registering event...\n");
if (VMI_SUCCESS == vmi_register_event(vmi, &rng_event)) {; // register the event!
printf("Event Registered!\n");
} else { // uh oh, event failed
printf("Problem registering event... exiting.\n");
ret_val = 6;
goto error_exit; // don't return directly, do cleanup first
}
// resume the VM
printf("Resuming the VM\n");
vmi_resume_vm(vmi);
//////////////////////////////////////
// Spin and wait for event callback //
//////////////////////////////////////
// for a clean exit, catch signals (from host, not VM), set "interrupted" to non-zero, exit while loop at end of main()
signal_action.sa_handler = close_handler;
signal_action.sa_flags = 0;
sigemptyset(&signal_action.sa_mask);
sigaction(SIGHUP, &signal_action, NULL);
sigaction(SIGTERM, &signal_action, NULL);
sigaction(SIGINT, &signal_action, NULL);
sigaction(SIGALRM, &signal_action, NULL);
while(!interrupted) { // until an interrupt happens
printf("Waiting for events...\n");
if (VMI_SUCCESS != vmi_events_listen(vmi, 500)) { // listen for events for 500ms (no event = VMI_SUCCESS)
printf("Error waiting for events... exiting.\n");
interrupted = -1;
}
}
printf("Finished with test.\n");
//////////////////
// Exit cleanly //
//////////////////
error_exit:
// attempt to remove breakpoints
for (int i = 0; i < num_breakpoints; i++) { // iterate over breakpoints and insert them all
// assign short names (note: modifying these modifies the breakpoint struct)
add = &breakpoints[i].addr;
bpid = &breakpoints[i].pid;
byt = &breakpoints[i].inst_byte;
printf("[pid %d] Removing breakpoint %d at 0x%llx.\n", *bpid, i, *add);
if (VMI_SUCCESS != vmi_write_8_va(vmi, *add, *bpid, byt)) {
printf("Couldn't write to memory... exiting.\n");
ret_val = 7;
}
}
// resume the vm
printf("Resuming the VM\n");
vmi_resume_vm(vmi);
// cleanup any memory associated with the LibVMI instance
printf("Cleaning up\n");
vmi_destroy(vmi);
return ret_val;
}
