Allow for tcb migration of sealed files

Signed-off-by: njeans <nerlajeanlouis@gmail.com>

Author: njeans

Documentation/devel/encfiles.rst

@@ -542,3 +542,14 @@ Additional details
     file data. Therefore, the usual NIST limits on the total number of
     invocations of the encryption operation with the same key would be reached
     much slower.
+
+- TCB migration: Gramine supports migration between different CPU SVN versions
+  by enabling it using the ``allow_tcb_migration`` mount parameter in the 
+  Gramine manifest. This feature allows encrypted files to be accessed even when 
+  the CPU SVN has changed after applying microcode updates. The current CPU SVN 
+  is stored in the mount directory in a file named ``gramine.tcb_info``. On 
+  startup if the CPU SVN has changed, Gramine will unseal the files using the 
+  old CPU SVN and reseal them with the current CPU SVN. This feature can negatively
+  impact integrity of files, as it allows files from a platform with a lower 
+  security level to be used. It is recommended to use this feature only in controlled
+  environments where the security implications are understood.

Documentation/devel/features.md

@@ -1314,6 +1314,8 @@ grows with time, as Gramine adds functionality required by real-world workloads.
       - ☑ `/dev/attestation/keys/<key_name>` <sup>[25](#attestation)</sup>
       - ☑ `/dev/attestation/keys/_sgx_mrenclave` <sup>[25](#attestation)</sup>
       - ☑ `/dev/attestation/keys/_sgx_mrsigner` <sup>[25](#attestation)</sup>
+      - ☑ `/dev/attestation/keys/svn/_sgx_mrenclave/<cpu_svn>` <sup>[25](#attestation)</sup>
+  - ☑ `/dev/attestation/cpu_svn` <sup>[25](#attestation)</sup>
   - ☑ `/dev/null` <sup>[23](#misc)</sup>
   - ☑ `/dev/zero` <sup>[23](#misc)</sup>
   - ☑ `/dev/random` <sup>[21](#randomness)</sup>
@@ -3245,6 +3247,10 @@ Gramine <low-level-dev-attestation-interface>`.
     - ☑ `/dev/attestation/keys/<key_name>`
     - ☑ `/dev/attestation/keys/_sgx_mrenclave` (only for SGX)
     - ☑ `/dev/attestation/keys/_sgx_mrsigner` (only for SGX)
+    - ☑ `/dev/attestation/keys/svn/_sgx_mrenclave/<cpu_svn>` (only for SGX)
+
+  - ☑ `/dev/attestation/cpu_svn` (only for SGX)
+
 
 </details><br />
 

Documentation/manifest-syntax.rst

@@ -1088,7 +1088,7 @@ Encrypted files
 ::
 
     fs.mounts = [
-      { type = "encrypted", path = "[PATH]", uri = "[URI]", key_name = "[KEY_NAME]", enable_recovery = [true|false] },
+      { type = "encrypted", path = "[PATH]", uri = "[URI]", key_name = "[KEY_NAME]", enable_recovery = [true|false], allow_tcb_migration = [true|false] },
     ]
 
     fs.insecure__keys.[KEY_NAME] = "[32-character hex value]"
@@ -1160,6 +1160,14 @@ or disabling of recovery for different mounted files or directories. Note that
 enabling this feature can negatively impact performance, as it writes to a
 second shadow file for later recovery purposes on each flush.
 
+The ``allow_tcb_migration`` mount parameter (default: ``false``) determines whether
+the TCB migration feature is enabled for the mount. This feature allows sealed files to
+be migrated to latest CPU SVN version after applying microcode updates.  This feature
+is only valid for ``key_name`` of ``"_sgx_mrenclave"``. Enabling this feature can
+negatively impact security, as it allow the enclave to unseal files that were created
+with an old potentially vulnerable CPU SVN version. It is the responsibility of the 
+app developer to verify the integrity of the sealed files if this feature is enabled.
+
 .. _untrusted-shared-memory:
 
 Untrusted shared memory

Documentation/pal/host-abi.rst

@@ -364,6 +364,15 @@ random bits, to obtain an attestation report and quote, etc.
 .. doxygenfunction:: PalGetSpecialKey
    :project: pal
 
+.. doxygenfunction:: PalGetSpecialKeyForSVN
+   :project: pal
+   
+.. doxygenfunction:: PalGetCPUSVN
+   :project: pal
+   
+.. doxygenfunction:: PalSetCPUSVN
+   :project: pal
+
 .. doxygenfunction:: PalDeviceMap
    :project: pal
 

libos/include/libos_fs.h

@@ -66,6 +66,10 @@ struct libos_mount_params {
     /* Whether to enable file recovery (used by `chroot_encrypted` filesystem), false if not
      * applicable */
     bool enable_recovery;
+
+    /* Whether to allow TCB migration (used by `chroot_encrypted` filesystem), false if not
+     * applicable */
+    bool allow_tcb_migration;
 };
 
 struct libos_fs_ops {

libos/include/libos_fs_encrypted.h

@@ -24,6 +24,16 @@
 
 #define RECOVERY_FILE_URI_SUFFIX ".gramine.recovery"
 
+#define TCB_INFO_PERM_RW PERM_rw_rw_r__
+
+#define TCB_INFO_FILE_NAME "gramine.tcb_info"
+
+#define CPU_SVN_SIZE 16
+
+#define OLD_TCB_FILE_URI_SUFFIX ".old_tcb"
+
+typedef uint8_t cpu_svn_t[CPU_SVN_SIZE];
+
 /*
  * Represents a named key for opening files. The key might not be set yet: value of a key can be
  * specified in the manifest, or set using `update_encrypted_files_key`. Before the key is set,
@@ -68,6 +78,13 @@ struct libos_encrypted_file {
  */
 int init_encrypted_files(void);
 
+/*
+ * \brief sets the default CPU SVN used for encrypted file keys.
+ *
+ * This is only used for testing.
+ */
+int set_cpu_svn(const cpu_svn_t* cpu_svn);
+
 /*
  * \brief Retrieve a key.
  *
@@ -95,6 +112,15 @@ int list_encrypted_files_keys(int (*callback)(struct libos_encrypted_files_key*
  */
 int get_or_create_encrypted_files_key(const char* name, struct libos_encrypted_files_key** out_key);
 
+/*
+ * \brief Retrieve a key with a CPU SVN.
+ *
+ * Sets `*out_key` to a key with given name and CPU SVN. Creates a new key.
+ *
+ */
+int create_encrypted_files_key_for_svn(const char* name, cpu_svn_t* cpu_svn,
+                                       struct libos_encrypted_files_key** out_key);
+
 /*
  * \brief Read value of given key.
  *
@@ -183,3 +209,5 @@ int encrypted_file_get_size(struct libos_encrypted_file* enc, file_off_t* out_si
 int encrypted_file_set_size(struct libos_encrypted_file* enc, file_off_t size);
 
 int parse_pf_key(const char* key_str, pf_key_t* pf_key);
+
+int handle_tcb_migration(const char* uri, const char* key_name);

libos/src/fs/chroot/encrypted.c

@@ -40,6 +40,7 @@
 #include "libos_fs.h"
 #include "libos_fs_encrypted.h"
 #include "libos_vma.h"
+#include "pal.h"
 #include "perm.h"
 #include "stat.h"
 #include "toml_utils.h"
@@ -60,16 +61,33 @@ static int chroot_encrypted_mount(struct libos_mount_params* params, void** moun
         log_error("'%s' is invalid file URI", params->uri);
         return -EINVAL;
     }
-
+    int ret;
     const char* key_name = params->key_name ?: "default";
 
+    if (params->allow_tcb_migration) {
+        if (!strcmp(key_name, PAL_KEY_NAME_SGX_MRENCLAVE)) {
+            log_warning("TCB migration will be supported for %s", params->uri);
+            ret = handle_tcb_migration(params->uri, key_name);
+            if (ret < 0) {
+                log_error("TCB migration failed for %s", params->uri);
+                return ret;
+            }
+
+        } else {
+            log_warning(
+                "TCB migration is only supported for keys named %s, ignoring "
+                "allow_tcb_migration for %s",
+                PAL_KEY_NAME_SGX_MRENCLAVE, params->uri);
+        }
+    }
     struct libos_encrypted_files_key* key;
-    int ret = get_or_create_encrypted_files_key(key_name, &key);
+    ret = get_or_create_encrypted_files_key(key_name, &key);
     if (ret < 0)
         return ret;
 
     *mount_data = key;
-    return 0;
+    return ret;
+
 }
 
 static ssize_t chroot_encrypted_checkpoint(void** checkpoint, void* mount_data) {

libos/src/fs/dev/attestation.c

@@ -16,6 +16,7 @@
  */
 
 #include "api.h"
+#include "hex.h"
 #include "libos_fs_encrypted.h"
 #include "libos_fs_pseudo.h"
 #include "pal.h"
@@ -84,6 +85,21 @@ static int user_report_data_save(struct libos_dentry* dent, const char* data, si
     return 0;
 }
 
+#ifdef DEBUG
+static int cpu_svn_save(struct libos_dentry* dent, const char* data, size_t size) {
+    log_debug("cpu_svn_save: saving %zu bytes", size);
+    __UNUSED(dent);
+    cpu_svn_t cpu_svn;
+    if (size != sizeof(cpu_svn)) {
+        log_warning("CPU SVN must be exactly %zu bytes, got %zu", sizeof(cpu_svn), size);
+        return -EINVAL;
+    }
+    memcpy(&cpu_svn, data, sizeof(cpu_svn));
+
+    return set_cpu_svn(&cpu_svn);
+}
+#endif /* DEBUG */
+
 /*!
  * \brief Modify target info used in `report` pseudo-file.
  *
@@ -239,6 +255,32 @@ static int quote_load(struct libos_dentry* dent, char** out_data, size_t* out_si
     return 0;
 }
 
+/*!
+ * \brief Get CPU SVN of the platform.
+ */
+static int cpu_svn_load(struct libos_dentry* dent, char** out_data, size_t* out_size) {
+    __UNUSED(dent);
+
+    cpu_svn_t cpu_svn;
+    size_t cpu_svn_size = sizeof(cpu_svn);
+    int ret = PalGetCPUSVN(&cpu_svn, &cpu_svn_size);
+    if (ret < 0) {
+        log_warning("PalGetCPUSVN failed: %s", pal_strerror(ret));
+        return pal_to_unix_errno(ret);
+    }
+
+    char* str = calloc(1, cpu_svn_size);
+
+    if (!str)
+        return -ENOMEM;
+
+    memcpy(str, &cpu_svn, sizeof(cpu_svn));
+
+    *out_data = str;
+    *out_size = cpu_svn_size;
+    return 0;
+}
+
 /*!
  * \brief Get remote attestation type used.
  *
@@ -264,6 +306,22 @@ static bool key_name_exists(struct libos_dentry* parent, const char* name) {
     return key != NULL;
 }
 
+static bool key_name_exists_svn(struct libos_dentry* parent, const char* name) {
+    __UNUSED(parent);
+    if (strlen(name) != 2 * sizeof(cpu_svn_t)) {
+        log_warning("key_name_exists_svn: invalid key name length %zu of %s, expected %zu",
+                    strlen(name), name, 2 * sizeof(cpu_svn_t));
+        return false;
+    }
+    cpu_svn_t cpu_svn;
+    if (!hex2bytes((char*)name, strlen(name), &cpu_svn, sizeof(cpu_svn_t))) {
+        log_warning("key_name_exists_svn: invalid key name format");
+        return false;
+    }
+
+    return true;
+}
+
 struct key_list_names_data {
     readdir_callback_t callback;
     void* arg;
@@ -284,6 +342,13 @@ static int key_list_names(struct libos_dentry* parent, readdir_callback_t callba
     return list_encrypted_files_keys(&key_list_names_callback, &data);
 }
 
+static int key_list_names_svn(struct libos_dentry* parent, readdir_callback_t callback, void* arg) {
+    __UNUSED(parent);
+    __UNUSED(callback);
+    __UNUSED(arg);
+    return 0;
+}
+
 static int key_load(struct libos_dentry* dent, char** out_data, size_t* out_size) {
     struct libos_encrypted_files_key* key = get_encrypted_files_key(dent->name);
     if (!key)
@@ -307,6 +372,58 @@ static int key_load(struct libos_dentry* dent, char** out_data, size_t* out_size
     return 0;
 }
 
+static int key_load_svn(struct libos_dentry* dent, char** out_data, size_t* out_size) {
+    if (strlen(dent->name) != 2 * sizeof(cpu_svn_t)) {
+        log_warning("key_name_exists_svn: invalid key name length");
+        return false;
+    }
+    cpu_svn_t cpu_svn;
+
+    if (!hex2bytes((char*)dent->name, strlen(dent->name), &cpu_svn, sizeof(cpu_svn_t))) {
+        log_warning("key_name_exists_svn: invalid key name format");
+        return false;
+    }
+
+    int ret;
+
+    char * key_name = dent->parent->name;
+    struct libos_encrypted_files_key* key = NULL;
+    key = calloc(1, sizeof(*key));
+    if (!key) {
+        log_error("Cannot allocate memory for key");
+        ret = -ENOMEM;
+        goto out;
+    }
+    ret = create_encrypted_files_key_for_svn(key_name, &cpu_svn, &key);
+    if (ret < 0) {
+        log_error("Cannot create or get key for SVN");
+        goto out;
+    }
+    pf_key_t pf_key;
+    bool is_set = read_encrypted_files_key(key, &pf_key);
+
+    if (is_set) {
+        char* buf = malloc(sizeof(pf_key));
+        if (!buf)
+            return -ENOMEM;
+        memcpy(buf, &pf_key, sizeof(pf_key));
+
+        *out_data = buf;
+        *out_size = sizeof(pf_key);
+    } else {
+        *out_data = NULL;
+        *out_size = 0;
+    }
+    ret = 0;
+out:
+    if (key) {
+        if (key->name)
+            free(key->name);
+        free(key);
+    }
+    return ret;
+}
+
 static int key_save(struct libos_dentry* dent, const char* data, size_t size) {
     struct libos_encrypted_files_key* key = get_encrypted_files_key(dent->name);
     if (!key)
@@ -338,6 +455,13 @@ static int init_sgx_attestation(struct pseudo_node* attestation, struct pseudo_n
     pseudo_add_str(attestation, "attestation_type", attestation_type_load);
     pseudo_add_str(attestation, "my_target_info", &my_target_info_load);
     pseudo_add_str(attestation, "report", &report_load);
+    struct pseudo_node* cpu_svn = pseudo_add_str(attestation, "cpu_svn", &cpu_svn_load);
+#ifdef DEBUG
+    cpu_svn->perm = PSEUDO_PERM_FILE_RW;
+    cpu_svn->str.save = &cpu_svn_save;
+#else
+    cpu_svn->perm = PSEUDO_PERM_FILE_R;
+#endif /* DEBUG */
 
     struct pseudo_node* user_report_data = pseudo_add_str(attestation, "user_report_data", NULL);
     user_report_data->perm = PSEUDO_PERM_FILE_RW;
@@ -362,6 +486,13 @@ static int init_sgx_attestation(struct pseudo_node* attestation, struct pseudo_n
     pseudo_add_str(keys, PAL_KEY_NAME_SGX_MRENCLAVE, &key_load);
     pseudo_add_str(keys, PAL_KEY_NAME_SGX_MRSIGNER, &key_load);
 
+    struct pseudo_node* keys_svn = pseudo_add_dir(keys, "svn");
+    struct pseudo_node* keys_svn_mrenclave_key =
+        pseudo_add_dir(keys_svn, PAL_KEY_NAME_SGX_MRENCLAVE);
+    struct pseudo_node* key_cpu_svn = pseudo_add_str(keys_svn_mrenclave_key, NULL, &key_load_svn);
+    key_cpu_svn->name_exists = &key_name_exists_svn;
+    key_cpu_svn->list_names = &key_list_names_svn;
+
     if (!strcmp(g_pal_public_state->attestation_type, "none")) {
         log_debug("host is Linux-SGX and remote attestation type is 'none', skipping "
                   "/dev/attestation/quote file");