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secret_prov_attest.c
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secret_prov_attest.c
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/* SPDX-License-Identifier: LGPL-3.0-or-later */
/* Copyright (C) 2020 Intel Labs */
/*!
* \file
*
* This file contains the implementation of secret provisioning library based on RA-TLS for
* enclavized application. It contains functions to create a self-signed RA-TLS certificate
* with an SGX quote embedded in it (using ra_tls_create_key_and_crt()), send it to one of
* the verifier/secret provisioning servers, and receive secrets in response.
*
* This file is part of the secret-provisioning client-side library which is typically linked
* into the SGX application that needs to receive secrets. This library is *not* thread-safe.
*/
#define STDC_WANT_LIB_EXT1 1
#define _XOPEN_SOURCE 700
#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "mbedtls/ctr_drbg.h"
#include "mbedtls/entropy.h"
#include "mbedtls/net_sockets.h"
#include "mbedtls/ssl.h"
#include "ra_tls.h"
#include "secret_prov.h"
#include "util.h"
/* these are globals because the user may continue using the SSL session even after invoking
* secret_provision_start() (in the user-supplied callback) */
static mbedtls_ctr_drbg_context g_ctr_drbg;
static mbedtls_entropy_context g_entropy;
static mbedtls_ssl_config g_conf;
static mbedtls_x509_crt g_verifier_ca_chain;
static mbedtls_net_context g_verifier_fd;
static mbedtls_ssl_context g_ssl;
static mbedtls_pk_context g_my_ratls_key;
static mbedtls_x509_crt g_my_ratls_cert;
static uint8_t* g_provisioned_secret = NULL;
static size_t g_provisioned_secret_size = 0;
void secret_provision_free_resources(void) {
mbedtls_x509_crt_free(&g_my_ratls_cert);
mbedtls_pk_free(&g_my_ratls_key);
mbedtls_net_free(&g_verifier_fd);
mbedtls_ssl_free(&g_ssl);
mbedtls_ssl_config_free(&g_conf);
mbedtls_x509_crt_free(&g_verifier_ca_chain);
mbedtls_ctr_drbg_free(&g_ctr_drbg);
mbedtls_entropy_free(&g_entropy);
}
int secret_provision_get(uint8_t** out_secret, size_t* out_secret_size) {
if (!out_secret || !out_secret_size)
return -EINVAL;
*out_secret = g_provisioned_secret;
*out_secret_size = g_provisioned_secret_size;
return 0;
}
void secret_provision_destroy(void) {
if (g_provisioned_secret && g_provisioned_secret_size)
#ifdef __STDC_LIB_EXT1__
memset_s(g_provisioned_secret, 0, g_provisioned_secret_size);
#else
memset(g_provisioned_secret, 0, g_provisioned_secret_size);
#endif
free(g_provisioned_secret);
g_provisioned_secret = NULL;
g_provisioned_secret_size = 0;
}
int secret_provision_start(const char* in_servers, const char* in_ca_chain_path,
struct ra_tls_ctx* out_ctx) {
int ret;
char* servers = NULL;
char* ca_chain_path = NULL;
char* connected_addr = NULL;
char* connected_port = NULL;
mbedtls_ctr_drbg_init(&g_ctr_drbg);
mbedtls_entropy_init(&g_entropy);
mbedtls_x509_crt_init(&g_verifier_ca_chain);
mbedtls_pk_init(&g_my_ratls_key);
mbedtls_x509_crt_init(&g_my_ratls_cert);
mbedtls_net_init(&g_verifier_fd);
mbedtls_ssl_config_init(&g_conf);
mbedtls_ssl_init(&g_ssl);
const char* pers = "secret-provisioning";
ret = mbedtls_ctr_drbg_seed(&g_ctr_drbg, mbedtls_entropy_func, &g_entropy,
(const uint8_t*)pers, strlen(pers));
if (ret < 0) {
goto out;
}
if (!in_ca_chain_path) {
in_ca_chain_path = getenv(SECRET_PROVISION_CA_CHAIN_PATH);
if (!in_ca_chain_path)
return -EINVAL;
}
ca_chain_path = strdup(in_ca_chain_path);
if (!ca_chain_path) {
ret = -ENOMEM;
goto out;
}
if (!in_servers) {
in_servers = getenv(SECRET_PROVISION_SERVERS);
if (!in_servers)
in_servers = DEFAULT_SERVERS;
}
servers = strdup(in_servers);
if (!servers) {
ret = -ENOMEM;
goto out;
}
char* saveptr1;
char* saveptr2;
char* str1;
for (str1 = servers; /*no condition*/; str1 = NULL) {
ret = -ECONNREFUSED;
char* token = strtok_r(str1, ",; ", &saveptr1);
if (!token)
break;
connected_addr = strtok_r(token, ":", &saveptr2);
if (!connected_addr)
continue;
connected_port = strtok_r(NULL, ":", &saveptr2);
if (!connected_port)
continue;
ret = mbedtls_net_connect(&g_verifier_fd, connected_addr, connected_port,
MBEDTLS_NET_PROTO_TCP);
if (!ret)
break;
}
if (ret < 0) {
goto out;
}
ret = mbedtls_ssl_config_defaults(&g_conf, MBEDTLS_SSL_IS_CLIENT, MBEDTLS_SSL_TRANSPORT_STREAM,
MBEDTLS_SSL_PRESET_DEFAULT);
if (ret < 0) {
goto out;
}
ret = mbedtls_x509_crt_parse_file(&g_verifier_ca_chain, ca_chain_path);
if (ret != 0) {
goto out;
}
char crt_issuer[256];
ret = mbedtls_x509_dn_gets(crt_issuer, sizeof(crt_issuer), &g_verifier_ca_chain.issuer);
if (ret < 0) {
goto out;
}
mbedtls_ssl_conf_authmode(&g_conf, MBEDTLS_SSL_VERIFY_REQUIRED);
mbedtls_ssl_conf_ca_chain(&g_conf, &g_verifier_ca_chain, NULL);
ret = ra_tls_create_key_and_crt(&g_my_ratls_key, &g_my_ratls_cert);
if (ret < 0) {
goto out;
}
mbedtls_ssl_conf_rng(&g_conf, mbedtls_ctr_drbg_random, &g_ctr_drbg);
ret = mbedtls_ssl_conf_own_cert(&g_conf, &g_my_ratls_cert, &g_my_ratls_key);
if (ret < 0) {
goto out;
}
ret = mbedtls_ssl_setup(&g_ssl, &g_conf);
if (ret < 0) {
goto out;
}
ret = mbedtls_ssl_set_hostname(&g_ssl, connected_addr);
if (ret < 0) {
goto out;
}
mbedtls_ssl_set_bio(&g_ssl, &g_verifier_fd, mbedtls_net_send, mbedtls_net_recv, NULL);
ret = -1;
while (ret < 0) {
ret = mbedtls_ssl_handshake(&g_ssl);
if (ret == MBEDTLS_ERR_SSL_WANT_READ || ret == MBEDTLS_ERR_SSL_WANT_WRITE) {
continue;
}
if (ret < 0) {
goto out;
}
}
uint32_t flags = mbedtls_ssl_get_verify_result(&g_ssl);
if (flags != 0) {
ret = MBEDTLS_ERR_X509_CERT_VERIFY_FAILED;
goto out;
}
struct ra_tls_ctx ctx = {.ssl = &g_ssl};
uint8_t buf[128] = {0};
size_t size;
static_assert(sizeof(buf) >= sizeof(SECRET_PROVISION_REQUEST),
"buffer must be sufficiently large to hold SECRET_PROVISION_REQUEST");
size = sprintf((char*)buf, SECRET_PROVISION_REQUEST);
size += 1; /* include null byte */
ret = secret_provision_write(&ctx, buf, size);
if (ret < 0) {
goto out;
}
/* remote verifier sends 32-bit integer over network; we need to ntoh it */
uint32_t received_secret_size;
static_assert(sizeof(buf) >= sizeof(SECRET_PROVISION_RESPONSE) + sizeof(received_secret_size),
"buffer must be sufficiently large to hold SECRET_PROVISION_RESPONSE + int32");
memset(buf, 0, sizeof(buf));
ret = secret_provision_read(&ctx, buf,
sizeof(SECRET_PROVISION_RESPONSE) + sizeof(received_secret_size));
if (ret < 0) {
goto out;
}
if (memcmp(buf, SECRET_PROVISION_RESPONSE, sizeof(SECRET_PROVISION_RESPONSE))) {
ret = -EINVAL;
goto out;
}
memcpy(&received_secret_size, buf + sizeof(SECRET_PROVISION_RESPONSE),
sizeof(received_secret_size));
received_secret_size = ntohl(received_secret_size);
if (received_secret_size > INT_MAX) {
ret = -EINVAL;
goto out;
}
/* destroy a previously provisioned secret, if any */
secret_provision_destroy();
g_provisioned_secret_size = received_secret_size;
g_provisioned_secret = malloc(g_provisioned_secret_size);
if (!g_provisioned_secret) {
ret = -ENOMEM;
goto out;
}
ret = secret_provision_read(&ctx, g_provisioned_secret, g_provisioned_secret_size);
if (ret < 0) {
goto out;
}
if (out_ctx) {
out_ctx->ssl = ctx.ssl;
} else {
secret_provision_close(&ctx);
}
ret = 0;
out:
if (ret < 0) {
secret_provision_destroy();
secret_provision_free_resources();
}
free(servers);
free(ca_chain_path);
return ret;
}
static bool truthy(const char* s) {
return !strcmp(s, "1") || !strcmp(s, "true") || !strcmp(s, "TRUE");
}
__attribute__((constructor)) static void secret_provision_constructor(void) {
const char* constructor = getenv(SECRET_PROVISION_CONSTRUCTOR);
if (constructor && truthy(constructor)) {
/* user wants to provision secret before application runs */
uint8_t* secret = NULL;
size_t secret_size = 0;
/* immediately unset envvar so that execve'd child processes do not land here (otherwise
* secret provisioning would happen for each new child, but each child already got all the
* secrets from the parent process during checkpoint-and-restore) */
unsetenv(SECRET_PROVISION_CONSTRUCTOR);
unsetenv(SECRET_PROVISION_SECRET_STRING);
int ret = secret_provision_start(/*in_servers=*/NULL, /*in_ca_chain_path=*/NULL,
/*out_ctx=*/NULL);
if (ret < 0)
return;
ret = secret_provision_get(&secret, &secret_size);
if (ret < 0 || !secret || !secret_size || secret_size > PATH_MAX ||
secret[secret_size - 1] != '\0') {
/* secret is not a null-terminated string, cannot do anything about such secret */
return;
}
/* successfully retrieved the secret: is it a key for encrypted files? */
const char* key_name = getenv(SECRET_PROVISION_SET_KEY);
if (!key_name) {
/* no key name specified - check old PF env var for compatibility */
const char* pf_key = getenv(SECRET_PROVISION_SET_PF_KEY);
if (pf_key && truthy(pf_key)) {
INFO(SECRET_PROVISION_SET_PF_KEY " is deprecated, consider setting "
SECRET_PROVISION_SET_KEY "=default instead.\n");
key_name = "default";
}
}
if (key_name) {
sgx_key_128bit_t keydata;
if (parse_hex((char*)secret, keydata, sizeof(keydata), "provisioned secret") < 0)
return;
char path_buf[256];
if (snprintf(path_buf, 256, "/dev/attestation/keys/%s", key_name) >= 256) {
ERROR("Key name '%s' too long\n", key_name);
return;
}
int fd = open(path_buf, O_WRONLY);
if (fd < 0)
return;
size_t total_written = 0;
while (total_written < sizeof(keydata)) {
ssize_t written = write(fd, keydata + total_written,
sizeof(keydata) - total_written);
if (written > 0) {
total_written += written;
} else if (written == 0) {
/* end of file */
break;
} else if (errno == EAGAIN || errno == EINTR) {
continue;
} else {
close(fd);
return;
}
}
close(fd); /* applies retrieved encryption key */
}
/* put the secret into an environment variable */
setenv(SECRET_PROVISION_SECRET_STRING, (const char*)secret, /*overwrite=*/1);
secret_provision_destroy();
}
}