arm64: Fix again segfault in arm64_is_kernel_exception_frame() when c…

…orrupt stack pointer address is given

This is the second trial from the commit
9868ebc that was reverted at the
previous commit.

As described in the previous commit, result of STACK_OFFSET_TYPE() can
be an address out of bt->stackbuf and hence the address needs to be
checked prior to being referred to as an pt_regs object.

So, to fix the issue, let's check if stkptr points to within the range
of the kernel stack first.

[ kh: added a warning at Lianbo's suggestion ]

Signed-off-by: HATAYAMA Daisuke <d.hatayama@fujitsu.com>

arm64.c

@@ -2381,6 +2381,12 @@ arm64_is_kernel_exception_frame(struct bt_info *bt, ulong stkptr)
         struct arm64_pt_regs *regs;
 	struct machine_specific *ms = machdep->machspec;
 
+	if (stkptr > STACKSIZE() && !INSTACK(stkptr, bt)) {
+		if (CRASHDEBUG(1))
+			error(WARNING, "stkptr: %lx is outside the kernel stack range\n", stkptr);
+		return FALSE;
+	}
+
         regs = (struct arm64_pt_regs *)&bt->stackbuf[(ulong)(STACK_OFFSET_TYPE(stkptr))];
 
 	if (INSTACK(regs->sp, bt) && INSTACK(regs->regs[29], bt) &&