s390/unwind: add stack pointer alignment sanity checks

ABI requires SP to be aligned 8 bytes, report unwinding error otherwise.

Link: https://lkml.kernel.org/r/20191106095601.29986-5-mbenes@suse.czReviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Tested-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/dumpstack.c

@@ -94,6 +94,10 @@ int get_stack_info(unsigned long sp, struct task_struct *task,
 	if (!sp)
 		goto unknown;
 
+	/* Sanity check: ABI requires SP to be aligned 8 bytes. */
+	if (sp & 0x7)
+		goto unknown;
+
 	/* Check per-task stack */
 	if (in_task_stack(sp, task, info))
 		goto recursion_check;

arch/s390/kernel/unwind_bc.c

@@ -92,6 +92,10 @@ bool unwind_next_frame(struct unwind_state *state)
 		}
 	}
 
+	/* Sanity check: ABI requires SP to be aligned 8 bytes. */
+	if (sp & 0x7)
+		goto out_err;
+
 	ip = ftrace_graph_ret_addr(state->task, &state->graph_idx, ip, (void *) sp);
 
 	/* Update unwind state */