ffi_tpm2.cpp

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/*
* (C) 2024 Jack Lloyd
* (C) 2024 René Meusel, Amos Treiber - Rohde & Schwarz Cybersecurity GmbH
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/ffi.h>
 
#include <botan/internal/ffi_pkey.h>
#include <botan/internal/ffi_rng.h>
#include <botan/internal/ffi_util.h>
 
#if defined(BOTAN_HAS_TPM2)
   #include <botan/tpm2_context.h>
   #include <botan/tpm2_key.h>
   #include <botan/tpm2_rng.h>
   #include <botan/tpm2_session.h>
#endif
 
extern "C" {
 
using namespace Botan_FFI;
 
#if defined(BOTAN_HAS_TPM2)
 
// These wrappers are required since BOTAN_FFI_DECLARE_STRUCT internally
// produces a unique pointer, but the TPM types are meant to be used as
// shared pointers.
 
struct botan_tpm2_ctx_wrapper {
      std::shared_ptr<Botan::TPM2::Context> ctx;
};
 
struct botan_tpm2_session_wrapper {
      std::shared_ptr<Botan::TPM2::Session> session;
};
 
BOTAN_FFI_DECLARE_STRUCT(botan_tpm2_ctx_struct, botan_tpm2_ctx_wrapper, 0xD2B95E15);
BOTAN_FFI_DECLARE_STRUCT(botan_tpm2_session_struct, botan_tpm2_session_wrapper, 0x9ACCAB52);
 
}  // extern "C"
 
namespace {
 
Botan::TPM2::SessionBundle sessions(botan_tpm2_session_t s1, botan_tpm2_session_t s2, botan_tpm2_session_t s3) {
   return Botan::TPM2::SessionBundle((s1 != nullptr) ? safe_get(s1).session : nullptr,
                                     (s2 != nullptr) ? safe_get(s2).session : nullptr,
                                     (s3 != nullptr) ? safe_get(s3).session : nullptr);
}
 
}  // namespace
 
extern "C" {
 
#endif
 
int botan_tpm2_supports_crypto_backend() {
#if defined(BOTAN_HAS_TPM2)
   return Botan::TPM2::Context::supports_botan_crypto_backend() ? 1 : 0;
#else
   return 0;
#endif
}
 
int botan_tpm2_ctx_init(botan_tpm2_ctx_t* ctx_out, const char* tcti_nameconf) {
#if defined(BOTAN_HAS_TPM2)
   return ffi_guard_thunk(__func__, [=]() -> int {
      if(ctx_out == nullptr) {
         return BOTAN_FFI_ERROR_NULL_POINTER;
      }
      auto ctx = std::make_unique<botan_tpm2_ctx_wrapper>();
 
      auto tcti = [=]() -> std::optional<std::string> {
         if(tcti_nameconf == nullptr) {
            return {};
         } else {
            return std::string(tcti_nameconf);
         }
      }();
 
      ctx->ctx = Botan::TPM2::Context::create(std::move(tcti));
      *ctx_out = new botan_tpm2_ctx_struct(std::move(ctx));
      return BOTAN_FFI_SUCCESS;
   });
#else
   BOTAN_UNUSED(ctx_out, tcti_nameconf);
   return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
#endif
}
 
int botan_tpm2_ctx_init_ex(botan_tpm2_ctx_t* ctx_out, const char* tcti_name, const char* tcti_conf) {
#if defined(BOTAN_HAS_TPM2)
   return ffi_guard_thunk(__func__, [=]() -> int {
      if(ctx_out == nullptr) {
         return BOTAN_FFI_ERROR_NULL_POINTER;
      }
      auto ctx = std::make_unique<botan_tpm2_ctx_wrapper>();
 
      auto tcti_name_str = [=]() -> std::optional<std::string> {
         if(tcti_name == nullptr) {
            return {};
         } else {
            return std::string(tcti_name);
         }
      }();
 
      auto tcti_conf_str = [=]() -> std::optional<std::string> {
         if(tcti_conf == nullptr) {
            return {};
         } else {
            return std::string(tcti_conf);
         }
      }();
 
      ctx->ctx = Botan::TPM2::Context::create(std::move(tcti_name_str), std::move(tcti_conf_str));
      *ctx_out = new botan_tpm2_ctx_struct(std::move(ctx));
      return BOTAN_FFI_SUCCESS;
   });
#else
   BOTAN_UNUSED(ctx_out, tcti_name, tcti_conf);
   return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
#endif
}
 
int botan_tpm2_ctx_enable_crypto_backend(botan_tpm2_ctx_t ctx, botan_rng_t rng) {
#if defined(BOTAN_HAS_TPM2)
   return BOTAN_FFI_VISIT(ctx, [=](botan_tpm2_ctx_wrapper& ctx_wrapper) -> int {
      Botan::RandomNumberGenerator& rng_ref = safe_get(rng);
 
      // The lifetime of the RNG used for the crypto backend should be managed
      // by the TPM2::Context. Here, we just need to trust the user that they
      // keep the passed-in RNG instance intact for the lifetime of the context.
      std::shared_ptr<Botan::RandomNumberGenerator> rng_ptr(&rng_ref, [](auto*) {});
      ctx_wrapper.ctx->use_botan_crypto_backend(rng_ptr);
      return BOTAN_FFI_SUCCESS;
   });
#else
   BOTAN_UNUSED(ctx, rng);
   return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
#endif
}
 
/**
 * Frees all resouces of a TPM2 context
 * @param ctx TPM2 context
 * @return 0 on success
 */
int botan_tpm2_ctx_destroy(botan_tpm2_ctx_t ctx) {
#if defined(BOTAN_HAS_TPM2)
   return BOTAN_FFI_CHECKED_DELETE(ctx);
#else
   BOTAN_UNUSED(ctx);
   return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
#endif
}
 
int botan_tpm2_rng_init(botan_rng_t* rng_out,
                        botan_tpm2_ctx_t ctx,
                        botan_tpm2_session_t s1,
                        botan_tpm2_session_t s2,
                        botan_tpm2_session_t s3) {
#if defined(BOTAN_HAS_TPM2)
   return BOTAN_FFI_VISIT(ctx, [=](botan_tpm2_ctx_wrapper& ctx_wrapper) -> int {
      if(rng_out == nullptr) {
         return BOTAN_FFI_ERROR_NULL_POINTER;
      }
 
      *rng_out = new botan_rng_struct(
         std::make_unique<Botan::TPM2::RandomNumberGenerator>(ctx_wrapper.ctx, sessions(s1, s2, s3)));
      return BOTAN_FFI_SUCCESS;
   });
#else
   BOTAN_UNUSED(rng_out, ctx, s1, s2, s3);
   return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
#endif
}
 
int botan_tpm2_unauthenticated_session_init(botan_tpm2_session_t* session_out, botan_tpm2_ctx_t ctx) {
#if defined(BOTAN_HAS_TPM2)
   return BOTAN_FFI_VISIT(ctx, [=](botan_tpm2_ctx_wrapper& ctx_wrapper) -> int {
      if(session_out == nullptr) {
         return BOTAN_FFI_ERROR_NULL_POINTER;
      }
 
      auto session = std::make_unique<botan_tpm2_session_wrapper>();
      session->session = Botan::TPM2::Session::unauthenticated_session(ctx_wrapper.ctx);
      *session_out = new botan_tpm2_session_struct(std::move(session));
      return BOTAN_FFI_SUCCESS;
   });
#else
   BOTAN_UNUSED(session_out, ctx);
   return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
#endif
}
 
int botan_tpm2_session_destroy(botan_tpm2_session_t session) {
#if defined(BOTAN_HAS_TPM2)
   return BOTAN_FFI_CHECKED_DELETE(session);
#else
   BOTAN_UNUSED(session);
   return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
#endif
}
}