core: REE FS: use RPMB for hash storage

REE FS uses RPMB (if available) for storage of dirfile hash.

Acked-by: Jerome Forissier <[email protected]>
Acked-by: Volodymyr Babchuk <[email protected]>
Signed-off-by: Jens Wiklander <[email protected]>

core/tee/tee_ree_fs.c

@@ -460,6 +460,59 @@ static const struct tee_fs_dirfile_operations ree_dirf_ops = {
 static struct tee_fs_dirfile_dirh *ree_fs_dirh;
 static size_t ree_fs_dirh_refcount;
 
+#ifdef CFG_RPMB_FS
+static struct tee_file_handle *ree_fs_rpmb_fh;
+
+static TEE_Result open_dirh(struct tee_fs_dirfile_dirh **dirh)
+{
+	TEE_Result res;
+	uint8_t hash[TEE_FS_HTREE_HASH_SIZE];
+	uint8_t *hashp = NULL;
+	const char fname[] = "dirfile.db.hash";
+
+	res = tee_rpmb_fs_raw_open(fname, false, &ree_fs_rpmb_fh);
+	if (!res) {
+		size_t l = sizeof(hash);
+
+		res = rpmb_fs_ops.read(ree_fs_rpmb_fh, 0, hash, &l);
+		if (res)
+			return res;
+		if (l == sizeof(hash))
+			hashp = hash;
+	} else if (res == TEE_ERROR_ITEM_NOT_FOUND) {
+		res = tee_rpmb_fs_raw_open(fname, true, &ree_fs_rpmb_fh);
+	}
+	if (res)
+		return res;
+
+	if (!tee_fs_dirfile_open(false, hashp, &ree_dirf_ops, dirh))
+		return TEE_SUCCESS;
+
+	res = tee_fs_dirfile_open(true, NULL, &ree_dirf_ops, dirh);
+	if (res)
+		rpmb_fs_ops.close(&ree_fs_rpmb_fh);
+	return res;
+}
+
+static TEE_Result commit_dirh_writes(struct tee_fs_dirfile_dirh *dirh)
+{
+	TEE_Result res;
+	uint8_t hash[TEE_FS_HTREE_HASH_SIZE];
+
+	res = tee_fs_dirfile_commit_writes(dirh, hash);
+	if (res)
+		return res;
+	return rpmb_fs_ops.write(ree_fs_rpmb_fh, 0, hash, sizeof(hash));
+}
+
+static void close_dirh(struct tee_fs_dirfile_dirh **dirh)
+{
+	tee_fs_dirfile_close(*dirh);
+	*dirh = NULL;
+	rpmb_fs_ops.close(&ree_fs_rpmb_fh);
+}
+
+#else /*!CFG_RPMB_FS*/
 static TEE_Result open_dirh(struct tee_fs_dirfile_dirh **dirh)
 {
 	if (!tee_fs_dirfile_open(false, NULL, &ree_dirf_ops, dirh))
@@ -477,6 +530,7 @@ static void close_dirh(struct tee_fs_dirfile_dirh **dirh)
 	tee_fs_dirfile_close(*dirh);
 	*dirh = NULL;
 }
+#endif /*!CFG_RPMB_FS*/
 
 static TEE_Result get_dirh(struct tee_fs_dirfile_dirh **dirh)
 {

core/tee/tee_svc.c

@@ -103,7 +103,11 @@ static const uint32_t crypto_ecc_en;
  * 100: Antirollback enforced at REE level
  * 1000: Antirollback TEE-controlled hardware
  */
+#ifdef CFG_RPMB_FS
+static const uint32_t ts_antiroll_prot_lvl = 1000;
+#else
 static const uint32_t ts_antiroll_prot_lvl;
+#endif
 
 /* Trusted OS implementation version */
 static const char trustedos_impl_version[] = TO_STR(TEE_IMPL_VERSION);

documentation/secure_storage.md

@@ -74,8 +74,9 @@ Below is an excerpt from the specification listing the most vital requirements:
    Typically, an implementation may rely on the REE for that purpose (protection
    level 100) or on hardware assets controlled by the TEE (protection level
    1000).
-   The current implementation does *not* provide any protection against
-   rollback, and therefore the protection level is set to 0.
+   If configured with CFG_RPMB_FS=y the protection against rollback is is
+   controlled by the TEE and is set to 1000. If CFG_RPMB_FS=n, there's no
+   protection against rollback, and the protection level is set to 0.
 
 ### TEE File Structure In Linux File System
 
@@ -223,17 +224,6 @@ implementations in your platform code for:
 These implementations should fetch the key data from your SoC-specific e-fuses,
 or crypto unit according to the method defined by your SoC vendor.
 
-## Future Work
-
-- **Rollback attack detection**
-
-An attacker can backup the whole `/data/tee` folder and restore it at later
-time.
-
-The basic idea of detecting rollback attack is to store information
-representing the state of `/data/tee/dirf.db` into another storage which has
-anti-rollback capability such as the eMMC RPMB partition.
-
 ## Reference
 
 * [Secure Storage Presentation](http://www.slideshare.net/linaroorg/sfo15503-secure-storage-in-optee)

documentation/secure_storage_rpmb.md

@@ -132,6 +132,12 @@ CBC block encryption is used only for RPMB (the REE implementation uses GCM).
 
 The FAT is not encrypted.
 
+## REE FS
+
+If configured with both CFG_REE_FS=y and CFG_RPMB_FS=y the REE FS will
+create a special file, "dirfile.db.hash" in RPMB which hold a hash
+representing the state of REE FS.
+
 ## References
 
 - <a name="JEDECeMMC"></a>[1] _Embedded Multi-Media Card (e•MMC) Electrical Standard (5.1)_, JEDEC JESD84-B51, February 2015