Graphene-SGX PF Data Structure

April 14, 2021 at 6:37 pm

pf_contex

struct pf_context {
    metadata_node_t file_metadata; // actual data from disk's meta data node
    pf_status_t last_error;
    metadata_encrypted_t encrypted_part_plain; // encrypted part of metadata node, decrypted
    file_node_t root_mht; // the root of the mht is always needed (for files bigger than 3KB)
    pf_handle_t file;
    pf_file_mode_t mode;
    uint64_t offset; // current file position (user's view)
    bool end_of_file;
    uint64_t real_file_size;
    bool need_writing;
    pf_status_t file_status;
    pf_key_t user_kdk_key;
    pf_key_t cur_key;
    lruc_context_t* cache;
#ifdef DEBUG
    char* debug_buffer; // buffer for debug output
#endif
};

See also: SGX_PF_Class

How nodes organized

In the PF implementation, there is a function called get_node_numbers, and the comments implies the node structure of a PF:

  • What's child MHT node? why 32?
  • Three types of nodes: metadata, data, and mht
  • metadata: TODO
  • data: just to store encrypted data
  • mht: each mht node can contain key and gmac of 96 data nodes and 32 child mht nodes. Every pf has at least one root mht node, and a mht (child) node is added to this pf after every 96 consecutive data nodes.
// this is a very 'specific' function, tied to the architecture of the file layout,
// returning the node numbers according to the data offset in the file
static void get_node_numbers(uint64_t offset, uint64_t* mht_node_number, uint64_t* data_node_number,
                             uint64_t* physical_mht_node_number,
                             uint64_t* physical_data_node_number) {
    // physical nodes (file layout):
    // node 0 - meta data node
    // node 1 - mht
    // nodes 2-97 - data (ATTACHED_DATA_NODES_COUNT == 96)
    // node 98 - mht
    // node 99-195 - data
    // etc.
    uint64_t _physical_mht_node_number;
    uint64_t _physical_data_node_number;

    // "logical" nodes: sequential index of the corresponding mht/data node in all mht/data nodes
    uint64_t _mht_node_number;
    uint64_t _data_node_number;

    assert(offset >= MD_USER_DATA_SIZE);

    _data_node_number = (offset - MD_USER_DATA_SIZE) / PF_NODE_SIZE;
    _mht_node_number = _data_node_number / ATTACHED_DATA_NODES_COUNT;
    _physical_data_node_number = _data_node_number
                                 + 1 // meta data node
                                 + 1 // mht root
                                 + _mht_node_number; // number of mht nodes in the middle
                                 // (the root mht mht_node_number is 0)
    _physical_mht_node_number = _physical_data_node_number
                                - _data_node_number % ATTACHED_DATA_NODES_COUNT // now we are at
                                // the first data node attached to this mht node
                                - 1; // and now at the mht node itself!

    if (mht_node_number != NULL)
        *mht_node_number = _mht_node_number;
    if (data_node_number != NULL)
        *data_node_number = _data_node_number;
    if (physical_mht_node_number != NULL)
        *physical_mht_node_number = _physical_mht_node_number;
    if (physical_data_node_number != NULL)
        *physical_data_node_number = _physical_data_node_number;
}

file_node_t

  • This macro also defines a linked list of file_node_t
  • Two types of decrypted data in this node
DEFINE_LIST(_file_node);
typedef struct _file_node {
    LIST_TYPE(_file_node) list;
    uint8_t type;
    uint64_t node_number;
    struct _file_node* parent;
    bool need_writing;
    bool new_node;
    struct {
        uint64_t physical_node_number;
        encrypted_node_t encrypted; // the actual data from the disk
    };
    union { // decrypted data
        mht_node_t mht;
        data_node_t data;
    } decrypted;
} file_node_t;
DEFINE_LISTP(_file_node);

typedef struct _mht_node {
    gcm_crypto_data_t data_nodes_crypto[ATTACHED_DATA_NODES_COUNT];
    gcm_crypto_data_t mht_nodes_crypto[CHILD_MHT_NODES_COUNT];
} mht_node_t;

typedef struct _data_node {
    uint8_t data[PF_NODE_SIZE];
} data_node_t;

typedef struct _encrypted_node {
    uint8_t cipher[PF_NODE_SIZE];
} encrypted_node_t;

See also: SDK_PF_DataNode

metadata_node_t

  • It seems like in graphene pf, the metadata node will be padded rather than filled in with user data.
  • Similar to SDK: #define PF_NODE_SIZE 4096U and #define MD_USER_DATA_SIZE (PF_NODE_SIZE * 3 / 4)
typedef struct _metadata_node {
    metadata_plain_t          plain_part;
    metadata_encrypted_blob_t encrypted_part;
    metadata_padding_t        padding;
} metadata_node_t;

typedef struct _metadata_plain {
    uint64_t   file_id;
    uint8_t    major_version;
    uint8_t    minor_version;
    pf_keyid_t metadata_key_id;
    pf_mac_t   metadata_gmac; /* GCM mac */
} metadata_plain_t;

typedef struct _metadata_encrypted {
    char     path[PATH_MAX_SIZE];
    uint64_t size;
    pf_key_t mht_key;
    pf_mac_t mht_gmac;
    uint8_t  data[MD_USER_DATA_SIZE];
} metadata_encrypted_t;

typedef uint8_t metadata_encrypted_blob_t[sizeof(metadata_encrypted_t)];

typedef uint8_t metadata_padding_t[METADATA_NODE_SIZE -
                                   (sizeof(metadata_plain_t) + sizeof(metadata_encrypted_blob_t))];

See also: SDK_PF_metadata