lib/test_lockup: fix kernel pointer check for separate address spaces

test_kernel_ptr() uses access_ok() to figure out if a given address
points to user space instead of kernel space. However on architectures
that set CONFIG_ALTERNATE_USER_ADDRESS_SPACE, a pointer can be valid
for both, and the check always fails because access_ok() returns true.

Make the check for user space pointers conditional on the type of
address space layout.

Signed-off-by: Arnd Bergmann <[e-mail]>

lib/test_lockup.c

···
 		return false;
 
 	/* should be at least readable kernel address */
-	if (access_ok((void __user *)ptr, 1) ||
-	    access_ok((void __user *)ptr + size - 1, 1) ||
-	    get_kernel_nofault(buf, ptr) ||
+	if (!IS_ENABLED(CONFIG_ALTERNATE_USER_ADDRESS_SPACE) &&
+	    (access_ok((void __user *)ptr, 1) ||
+	     access_ok((void __user *)ptr + size - 1, 1))) {
+		pr_err("user space ptr invalid in kernel: %#lx\n", addr);
+		return true;
+	}
+
+	if (get_kernel_nofault(buf, ptr) ||
 	    get_kernel_nofault(buf, ptr + size - 1)) {
 		pr_err("invalid kernel ptr: %#lx\n", addr);
 		return true;