x86_64: check bt->bptr before calculate framesize

Previously the value of bt->bptr is not checked, which may led to a
wrong prev_sp and framesize. As a result, bt->stackbuf[] will be
accessed out of range, and segfault.

Before:
  crash> set debug 1
  crash> bt
  ...snip...
  --- <NMI exception stack> ---
   crash-utility#8 [ffffffff9a603e10] __switch_to_asm at ffffffff99800214
  rsp: ffffffff9a603e10 textaddr: ffffffff99800214 -> spo: 0 bpo: 0 spr: 0 bpr: 0 type: 0 end: 0
   crash-utility#9 [ffffffff9a603e40] __schedule at ffffffff9960dfb1
  rsp: ffffffff9a603e40 textaddr: ffffffff9960dfb1 -> spo: 16 bpo: -16 spr: 4 bpr: 1 type: 0 end: 0
  rsp: ffffffff9a603e40 rbp: ffffb9ca076e7ca8 prev_sp: ffffb9ca076e7cb8 framesize: 1829650024
  Segmentation fault (core dumped)

  (gdb) p/x bt->stackbase
  $1 = 0xffffffff9a600000
  (gdb) p/x bt->stacktop
  $2 = 0xffffffff9a604000

After:
  crash> set debug 1
  crash> bt
  ...snip...
  --- <NMI exception stack> ---
   crash-utility#8 [ffffffff9a603e10] __switch_to_asm at ffffffff99800214
  rsp: ffffffff9a603e10 textaddr: ffffffff99800214 -> spo: 0 bpo: 0 spr: 0 bpr: 0 type: 0 end: 0
   crash-utility#9 [ffffffff9a603e40] __schedule at ffffffff9960dfb1
  rsp: ffffffff9a603e40 textaddr: ffffffff9960dfb1 -> spo: 16 bpo: -16 spr: 4 bpr: 1 type: 0 end: 0
   crash-utility#10 [ffffffff9a603e98] schedule_idle at ffffffff9960e87c
  rsp: ffffffff9a603e98 textaddr: ffffffff9960e87c -> spo: 8 bpo: 0 spr: 5 bpr: 0 type: 0 end: 0
  rsp: ffffffff9a603e98 prev_sp: ffffffff9a603ea8 framesize: 0
  ...snip...

Check bt->bptr value before calculate framesize. Only bt->bptr within
the range of bt->stackbase and bt->stacktop will be regarded as valid.

Signed-off-by: Tao Liu <[email protected]>

x86_64.c

@@ -8649,7 +8649,7 @@ x86_64_get_framesize(struct bt_info *bt, ulong textaddr, ulong rsp, char *stack_
 				if (CRASHDEBUG(1))
 					fprintf(fp, "rsp: %lx prev_sp: %lx framesize: %d\n",
 							rsp, prev_sp, framesize);
-			} else if ((korc->sp_reg == ORC_REG_BP) && bt->bptr) {
+			} else if ((korc->sp_reg == ORC_REG_BP) && bt->bptr && INSTACK(bt->bptr, bt)) {
 				prev_sp = bt->bptr + korc->sp_offset;
 				framesize = (prev_sp - (rsp + 8) - 8);
 				if (CRASHDEBUG(1))