Blackfin: access_ok: permit L1 stack

When apps run with their stack in L1, some system calls might be made
where a buffer is in the stack as an argument.  So make sure the core
Blackfin access code does not reject this memory location.
Signed-off-by: Barry Song <barry.song@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/kernel/process.c

@@ -493,6 +493,11 @@ int _access_ok(unsigned long addr, unsigned long size)
 		return 1;
 #endif
 
+#ifndef CONFIG_EXCEPTION_L1_SCRATCH
+	if (in_mem_const(addr, size, (unsigned long)l1_stack_base, l1_stack_len))
+		return 1;
+#endif
+
 	aret = in_async(addr, size);
 	if (aret < 2)
 		return aret;