common/rollback: Add support for rollback protection

Implement actual rollback protection. First, we add a new field
in the version structure, which is an incrementing integer
(we'll start by shipping images with version 0, and gradually
increase the number as required). This allows us to release
new versions of the EC without necessarily bumping the rollback
protection.

For the rollback protection block itself, it contains 2 sub-blocks
of equal size (normally, 2k), that are individually erasable.
The rollback code looks at both, and takes the most restrictive one
to determine the desired rollback minimum version. The blocks
are also allowed to be erased (full of 1's), in which case the
rollback minimum version is assumed to be 0.

We also add an FMAP entry, in case we later decide to allow the
signer to increment the rollback version.

Also note that, like any version_data struct change, this change
breaks compatibility between old and new RO/RW.

Follow-up code will take care of auto-updating the rollback block
as required, and properly manage block protection.

BRANCH=none
BUG=b:35586219
TEST=Flash hammer
     rollbackinfo => 1 version 0 block, 1 empty block, RW verifies
           correctly.
     rollbackupdate 0; rollbackinfo => No change
     rollbackupdate 1; reboot => RO refuses to jump to RW
     rollbackupdate 2, 3, 4; rollbackinfo => Writes alternate
           between the 2 blocks.
     rollbackupdate 2 => Refuses to downgrade version

Change-Id: Ia969afb481a93deb912b9153bdd95ace01ad8fa7
Reviewed-on: https://chromium-review.googlesource.com/452815
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/include/rollback.h b/include/rollback.h
new file mode 100644
index 0000000000..7221691c1f
--- /dev/null
+++ b/include/rollback.h
@@ -0,0 +1,32 @@
+/* Copyright 2017 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef __CROS_EC_ROLLBACK_H
+#define __CROS_EC_ROLLBACK_H
+
+#define CROS_EC_ROLLBACK_COOKIE 0x0b112233
+
+#ifndef __ASSEMBLER__
+
+/**
+ * Get minimum version set by rollback protection blocks.
+ *
+ * @return Minimum rollback version, 0 if neither block is initialized,
+ * negative value on error.
+ */
+int rollback_get_minimum_version(void);
+
+/**
+ * Update rollback protection block to the version passed as parameter.
+ *
+ * @param next_min_version	Minimum version to write in rollback block.
+ *
+ * @return EC_SUCCESS on success, EC_ERROR_* on error.
+ */
+int rollback_update(int32_t next_min_version);
+
+#endif
+
+#endif  /* __CROS_EC_ROLLBACK_H */