tpm.cpp

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/*
* TPM 1.2 interface
* (C) 2015 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/tpm.h>
#include <botan/rsa.h>
#include <botan/hash.h>
#include <botan/hash_id.h>
#include <botan/der_enc.h>
#include <botan/workfactor.h>
#include <botan/pk_ops.h>
#include <sstream>

#include <tss/platform.h>
#include <tss/tspi.h>
#include <trousers/trousers.h>

// TODO: dynamically load the TPM libraries?

namespace Botan {

namespace {

void tss_error(TSS_RESULT res, const char* expr, const char* file, int line)
   {
   std::ostringstream err;
   err << "TPM error " << Trspi_Error_String(res)
       << " layer " << Trspi_Error_Layer(res)
       << " in " << expr << " at " << file << ":" << line;

   throw TPM_Error(err.str());
   }

TSS_FLAG bit_flag(size_t bits)
   {
   switch(bits)
      {
      // 512 supported, but ignored and rejected here
      case 1024:
         return TSS_KEY_SIZE_1024;
      case 2048:
         return TSS_KEY_SIZE_2048;

      // Most? v1.2 TPMs only support 1024 and 2048 bit keys ...
      case 4096:
         return TSS_KEY_SIZE_4096;
      case 8192:
         return TSS_KEY_SIZE_8192;
      case 16384:
         return TSS_KEY_SIZE_16384;
      default:
         throw Invalid_Argument("Unsupported TPM key size " + std::to_string(bits));
      }
   }

#if 0
bool is_srk_uuid(const UUID& uuid)
   {
   static const uint8_t srk[16] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 };
   const std::vector<uint8_t>& b = uuid.binary_value();
   return (b.size() == 16 && same_mem(b.data(), srk, 16));
   }
#endif

#define TSPI_CHECK_SUCCESS(expr) do {   \
   TSS_RESULT res = expr;           \
   if(res != TSS_SUCCESS)           \
      tss_error(res, #expr, __FILE__, __LINE__);         \
   } while(0)

std::vector<uint8_t> get_obj_attr(TSS_HCONTEXT ctx,
                                  TSS_HOBJECT obj,
                                  TSS_FLAG flag,
                                  TSS_FLAG sub_flag)
   {
   BYTE *data = nullptr;
   UINT32 data_len = 0;
   TSPI_CHECK_SUCCESS(::Tspi_GetAttribData(obj, flag, sub_flag, &data_len, &data));

   std::vector<uint8_t> r(data, data + data_len);

   TSPI_CHECK_SUCCESS(::Tspi_Context_FreeMemory(ctx, data));

   return r;
   }

void set_policy_secret(TSS_HPOLICY policy, const char* secret)
   {
   if(secret)
      {
      BYTE* as_b = const_cast<BYTE*>(reinterpret_cast<const BYTE*>(secret));
      TSPI_CHECK_SUCCESS(::Tspi_Policy_SetSecret(policy,
                                                 TSS_SECRET_MODE_PLAIN,
                                                 std::strlen(secret),
                                                 as_b));
      }
   else
      {
      static const uint8_t nullpass[20] = { 0 };

      TSPI_CHECK_SUCCESS(::Tspi_Policy_SetSecret(policy,
                                             TSS_SECRET_MODE_SHA1,
                                             sizeof(nullpass),
                                             const_cast<BYTE*>(nullpass)));
      }
   }

TSS_UUID to_tss_uuid(const UUID& uuid)
   {
   static_assert(sizeof(TSS_UUID) == 16, "Expected size of packed UUID");

   TSS_UUID tss_uuid;
   std::memcpy(&tss_uuid, uuid.binary_value().data(), 16);
   return tss_uuid;
   }

UUID from_tss_uuid(const TSS_UUID& tss_uuid)
   {
   static_assert(sizeof(TSS_UUID) == 16, "Expected size of packed UUID");

   std::vector<uint8_t> mem(16);
   std::memcpy(mem.data(), &tss_uuid, 16);
   UUID uuid(std::move(mem));
   return uuid;
   }

TPM_Storage_Type storage_type_from_tss_flag(TSS_FLAG flag)
   {
   if(flag == TSS_PS_TYPE_USER)
      return TPM_Storage_Type::User;
   else if(flag == TSS_PS_TYPE_SYSTEM)
      return TPM_Storage_Type::System;
   else
      throw TPM_Error("Invalid storage flag " + std::to_string(flag));
   }

std::string format_url(const UUID& uuid, TPM_Storage_Type storage)
   {
   std::string storage_str = (storage == TPM_Storage_Type::User) ? "user" : "system";
   return "tpmkey:uuid=" + uuid.to_string() + ";storage=" + storage_str;
   }

std::string format_url(const TSS_UUID& tss_uuid, TSS_FLAG store_type)
   {
   UUID uuid = from_tss_uuid(tss_uuid);

   return format_url(from_tss_uuid(tss_uuid),
                     storage_type_from_tss_flag(store_type));
   }

}

TPM_Context::TPM_Context(pin_cb cb, const char* srk_password) : m_pin_cb(cb)
   {
   TSPI_CHECK_SUCCESS(::Tspi_Context_Create(&m_ctx));
   TSPI_CHECK_SUCCESS(::Tspi_Context_Connect(m_ctx, nullptr));

   TSPI_CHECK_SUCCESS(::Tspi_Context_GetTpmObject(m_ctx, &m_tpm));

   const TSS_UUID SRK_UUID = TSS_UUID_SRK;

   TSPI_CHECK_SUCCESS(::Tspi_Context_LoadKeyByUUID(m_ctx, TSS_PS_TYPE_SYSTEM, SRK_UUID, &m_srk));

   TSS_HPOLICY srk_policy;
   TSPI_CHECK_SUCCESS(::Tspi_GetPolicyObject(m_srk, TSS_POLICY_USAGE, &srk_policy));
   set_policy_secret(srk_policy, srk_password);

   // TODO: leaking policy object here?
   // TODO: do we have to cache it?
   // TODO: try to use SRK with null, if it fails call the pin cb?
   }

TPM_Context::~TPM_Context()
   {
   TSPI_CHECK_SUCCESS(::Tspi_Context_CloseObject(m_ctx, m_srk));
   //TSPI_CHECK_SUCCESS(::Tspi_Context_CloseObject(m_ctx, m_tpm));
   TSPI_CHECK_SUCCESS(::Tspi_Context_Close(m_ctx));
   }

uint32_t TPM_Context::current_counter()
   {
   uint32_t r = 0;
   TSPI_CHECK_SUCCESS(::Tspi_TPM_ReadCounter(m_tpm, &r));
   return r;
   }

void TPM_Context::gen_random(uint8_t out[], size_t out_len)
   {
   BYTE* mem;
   TSPI_CHECK_SUCCESS(::Tspi_TPM_GetRandom(m_tpm, out_len, &mem));
   std::memcpy(out, mem, out_len);
   TSPI_CHECK_SUCCESS(::Tspi_Context_FreeMemory(m_ctx, mem));
   }

void TPM_Context::stir_random(const uint8_t in[], size_t in_len)
   {
   TSPI_CHECK_SUCCESS(::Tspi_TPM_StirRandom(m_tpm, in_len, const_cast<BYTE*>(in)));
   }

TPM_PrivateKey::TPM_PrivateKey(TPM_Context& ctx, size_t bits,
                               const char* key_password) : m_ctx(ctx)
   {
   // TODO: can also do OAEP decryption via binding keys
   // TODO: offer signing, binding (decrypt), or legacy (sign + decrypt) keys?

   TSS_FLAG key_flags = bit_flag(bits) | TSS_KEY_VOLATILE | TSS_KEY_TYPE_SIGNING;

   TSS_HKEY key;
   TSPI_CHECK_SUCCESS(::Tspi_Context_CreateObject(m_ctx.handle(), TSS_OBJECT_TYPE_RSAKEY, key_flags, &key));

   TSPI_CHECK_SUCCESS(::Tspi_SetAttribUint32(key, TSS_TSPATTRIB_KEY_INFO,
                                         TSS_TSPATTRIB_KEYINFO_SIGSCHEME,
                                         TSS_SS_RSASSAPKCS1V15_DER));

   TSS_HPOLICY policy;
   TSPI_CHECK_SUCCESS(::Tspi_Context_CreateObject(m_ctx.handle(), TSS_OBJECT_TYPE_POLICY, TSS_POLICY_USAGE, &policy));
   set_policy_secret(policy, key_password);
   TSPI_CHECK_SUCCESS(::Tspi_Policy_AssignToObject(policy, key));

   TSPI_CHECK_SUCCESS(::Tspi_Key_CreateKey(key, ctx.srk(), 0));
   m_key = key;
   }

// reference a registered TPM key
TPM_PrivateKey::TPM_PrivateKey(TPM_Context& ctx, const std::string& uuid_str,
                               TPM_Storage_Type storage_type) :
   m_ctx(ctx),
   m_uuid(uuid_str),
   m_storage(storage_type)
   {
   const TSS_FLAG key_ps_type =
      (m_storage == TPM_Storage_Type::User) ? TSS_PS_TYPE_USER : TSS_PS_TYPE_SYSTEM;

   TSPI_CHECK_SUCCESS(::Tspi_Context_LoadKeyByUUID(m_ctx.handle(),
                                               key_ps_type,
                                               to_tss_uuid(m_uuid),
                                               &m_key));
   }

TPM_PrivateKey::TPM_PrivateKey(TPM_Context& ctx,
                               const std::vector<uint8_t>& blob) : m_ctx(ctx)
   {
   TSPI_CHECK_SUCCESS(::Tspi_Context_LoadKeyByBlob(m_ctx.handle(), m_ctx.srk(), blob.size(),
                                               const_cast<uint8_t*>(blob.data()),
                                               &m_key));

   //TSPI_CHECK_SUCCESS(::Tspi_Key_LoadKey(m_key, m_ctx.srk()));
   }

std::string TPM_PrivateKey::register_key(TPM_Storage_Type storage_type)
   {
   if(!m_uuid.is_valid())
      {
      TPM_RNG rng(ctx()); // use system_rng or arg RNG& instead?
      m_uuid = UUID(rng);
      m_storage = storage_type;

      const TSS_UUID key_uuid = to_tss_uuid(m_uuid);
      const TSS_FLAG key_ps_type =
         (storage_type == TPM_Storage_Type::User) ? TSS_PS_TYPE_USER : TSS_PS_TYPE_SYSTEM;

      const TSS_UUID srk_uuid = TSS_UUID_SRK;

      TSPI_CHECK_SUCCESS(::Tspi_Context_RegisterKey(m_ctx.handle(),
                                                m_key,
                                                key_ps_type,
                                                key_uuid,
                                                TSS_PS_TYPE_SYSTEM,
                                                srk_uuid));

      }

   // Presumably we could re-register in the other store and same UUID
   // Doesn't seem like what is desired most of the time here
   if(storage_type != m_storage)
      {
      throw TPM_Error("TPM key " + m_uuid.to_string() +
                      " already registered with different storage type");
      }

   return format_url(m_uuid, m_storage);
   }

std::vector<std::string> TPM_PrivateKey::registered_keys(TPM_Context& ctx)
   {
   TSS_KM_KEYINFO2* key_info;
   UINT32 key_info_size;

   // TODO: does the PS type matter here at all?
   TSPI_CHECK_SUCCESS(::Tspi_Context_GetRegisteredKeysByUUID2(ctx.handle(),
                                                          TSS_PS_TYPE_SYSTEM,
                                                          nullptr,
                                                          &key_info_size,
                                                          &key_info));

   std::vector<std::string> r(key_info_size);

   for(size_t i = 0; i != key_info_size; ++i)
      {
      r[i] = format_url(key_info[i].keyUUID, key_info[i].persistentStorageType);
      }

   // TODO: are we supposed to free this memory and if so how?
   //TSPI_CHECK_SUCCESS(::Tspi_Context_FreeMemory(ctx.handle(), key_info));

   return r;
   }

BigInt TPM_PrivateKey::get_n() const
   {
   if(m_n == 0)
      {
      m_n = BigInt::decode(get_obj_attr(m_ctx.handle(), m_key,
                                        TSS_TSPATTRIB_RSAKEY_INFO,
                                        TSS_TSPATTRIB_KEYINFO_RSA_MODULUS));
      }

   return m_n;
   }

BigInt TPM_PrivateKey::get_e() const
   {
   if(m_e == 0)
      {
      m_e = BigInt::decode(get_obj_attr(m_ctx.handle(), m_key,
                                        TSS_TSPATTRIB_RSAKEY_INFO,
                                        TSS_TSPATTRIB_KEYINFO_RSA_EXPONENT));
      }

   return m_e;
   }

size_t TPM_PrivateKey::estimated_strength() const
   {
   return if_work_factor(key_length());
   }

size_t TPM_PrivateKey::key_length() const
   {
   return get_n().bits();
   }

AlgorithmIdentifier TPM_PrivateKey::algorithm_identifier() const
   {
   return AlgorithmIdentifier(get_oid(),
                              AlgorithmIdentifier::USE_NULL_PARAM);
   }

std::vector<uint8_t> TPM_PrivateKey::public_key_bits() const
   {
   return DER_Encoder()
      .start_cons(SEQUENCE)
        .encode(get_n())
        .encode(get_e())
      .end_cons()
      .get_contents_unlocked();
   }

secure_vector<uint8_t> TPM_PrivateKey::private_key_bits() const
   {
   throw TPM_Error("Private key export not supported for TPM keys");
   }

std::vector<uint8_t> TPM_PrivateKey::export_blob() const
   {
   return get_obj_attr(m_ctx.handle(), m_key,
                       TSS_TSPATTRIB_KEY_BLOB,
                       TSS_TSPATTRIB_KEYBLOB_BLOB);
   }

std::unique_ptr<Public_Key> TPM_PrivateKey::public_key() const
   {
   return std::unique_ptr<Public_Key>(new RSA_PublicKey(get_n(), get_e()));
   }

bool TPM_PrivateKey::check_key(RandomNumberGenerator&, bool) const
   {
   return true; // TODO do a kat or pairwise check
   }

namespace {

class TPM_Signing_Operation final : public PK_Ops::Signature
   {
   public:
      TPM_Signing_Operation(const TPM_PrivateKey& key,
                            const std::string& hash_name) :
         m_key(key),
         m_hash(HashFunction::create(hash_name)),
         m_hash_id(pkcs_hash_id(hash_name))
         {
         }

      void update(const uint8_t msg[], size_t msg_len) override
         {
         m_hash->update(msg, msg_len);
         }

      secure_vector<uint8_t> sign(RandomNumberGenerator&) override
         {
         /*
         * v1.2 TPMs will only sign with PKCS #1 v1.5 padding. SHA-1 is built
         * in, all other hash inputs (TSS_HASH_OTHER) are treated as the
         * concatenation of the hash OID and hash value and signed with just the
         * 01FFFF... prefix. Even when using SHA-1 we compute the hash locally
         * since it is going to be much faster than pushing data over the LPC bus.
         */
         secure_vector<uint8_t> msg_hash = m_hash->final();

         std::vector<uint8_t> id_and_msg;
         id_and_msg.reserve(m_hash_id.size() + msg_hash.size());
         id_and_msg.insert(id_and_msg.end(), m_hash_id.begin(), m_hash_id.end());
         id_and_msg.insert(id_and_msg.end(), msg_hash.begin(), msg_hash.end());

         TSS_HCONTEXT ctx = m_key.ctx().handle();
         TSS_HHASH tpm_hash;
         TSPI_CHECK_SUCCESS(::Tspi_Context_CreateObject(ctx, TSS_OBJECT_TYPE_HASH, TSS_HASH_OTHER, &tpm_hash));
         TSPI_CHECK_SUCCESS(::Tspi_Hash_SetHashValue(tpm_hash, id_and_msg.size(), id_and_msg.data()));

         BYTE* sig_bytes = nullptr;
         UINT32 sig_len = 0;
         TSPI_CHECK_SUCCESS(::Tspi_Hash_Sign(tpm_hash, m_key.handle(), &sig_len, &sig_bytes));
         secure_vector<uint8_t> sig(sig_bytes, sig_bytes + sig_len);

         // TODO: RAII for Context_FreeMemory
         TSPI_CHECK_SUCCESS(::Tspi_Context_FreeMemory(ctx, sig_bytes));

         // TODO: RAII for Context_CloseObject
         TSPI_CHECK_SUCCESS(::Tspi_Context_CloseObject(ctx, tpm_hash));

         return sig;
         }

   private:
      const TPM_PrivateKey& m_key;
      std::unique_ptr<HashFunction> m_hash;
      std::vector<uint8_t> m_hash_id;
   };

}

std::unique_ptr<PK_Ops::Signature>
TPM_PrivateKey::create_signature_op(RandomNumberGenerator& /*rng*/,
                                    const std::string& params,
                                    const std::string& /*provider*/) const
   {
   return std::unique_ptr<PK_Ops::Signature>(new TPM_Signing_Operation(*this, params));
   }

}