bpf: force strict alignment checks for stack pointers

thejh · borkmann · commit a5ec6ae161d7 · 2017-12-21T02:15:41.000+01:00
Force strict alignment checks for stack pointers because the tracking of stack spills relies on it; unaligned stack accesses can lead to corruption of spilled registers, which is exploitable. Fixes: f1174f7 ("bpf/verifier: rework value tracking") Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
@@ -1059,6 +1059,11 @@ static int check_ptr_alignment(struct bpf_verifier_env *env,
 		break;
 	case PTR_TO_STACK:
 		pointer_desc = "stack ";
+		/* The stack spill tracking logic in check_stack_write()
+		 * and check_stack_read() relies on stack accesses being
+		 * aligned.
+		 */
+		strict = true;
 		break;
 	default:
 		break;
