hw/tpm/tpm_util.c

   1 /*
   2  * TPM utility functions
   3  *
   4  *  Copyright (c) 2010 - 2015 IBM Corporation
   5  *  Authors:
   6  *    Stefan Berger <stefanb@us.ibm.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2 of the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, see <http://www.gnu.org/licenses/>
  20  */
  21
  22 #include "tpm_util.h"
  23 #include "tpm_int.h"
  24
  25 /*
  26  * A basic test of a TPM device. We expect a well formatted response header
  27  * (error response is fine) within one second.
  28  */
  29 static int tpm_util_test(int fd,
  30                          unsigned char *request,
  31                          size_t requestlen,
  32                          uint16_t *return_tag)
  33 {
  34     struct tpm_resp_hdr *resp;
  35     fd_set readfds;
  36     int n;
  37     struct timeval tv = {
  38         .tv_sec = 1,
  39         .tv_usec = 0,
  40     };
  41     unsigned char buf[1024];
  42
  43     n = write(fd, request, requestlen);
  44     if (n < 0) {
  45         return errno;
  46     }
  47     if (n != requestlen) {
  48         return EFAULT;
  49     }
  50
  51     FD_ZERO(&readfds);
  52     FD_SET(fd, &readfds);
  53
  54     /* wait for a second */
  55     n = select(fd + 1, &readfds, NULL, NULL, &tv);
  56     if (n != 1) {
  57         return errno;
  58     }
  59
  60     n = read(fd, &buf, sizeof(buf));
  61     if (n < sizeof(struct tpm_resp_hdr)) {
  62         return EFAULT;
  63     }
  64
  65     resp = (struct tpm_resp_hdr *)buf;
  66     /* check the header */
  67     if (be32_to_cpu(resp->len) != n) {
  68         return EBADMSG;
  69     }
  70
  71     *return_tag = be16_to_cpu(resp->tag);
  72
  73     return 0;
  74 }
  75
  76 /*
  77  * Probe for the TPM device in the back
  78  * Returns 0 on success with the version of the probed TPM set, 1 on failure.
  79  */
  80 int tpm_util_test_tpmdev(int tpm_fd, TPMVersion *tpm_version)
  81 {
  82     /*
  83      * Sending a TPM1.2 command to a TPM2 should return a TPM1.2
  84      * header (tag = 0xc4) and error code (TPM_BADTAG = 0x1e)
  85      *
  86      * Sending a TPM2 command to a TPM 2 will give a TPM 2 tag in the
  87      * header.
  88      * Sending a TPM2 command to a TPM 1.2 will give a TPM 1.2 tag
  89      * in the header and an error code.
  90      */
  91     const struct tpm_req_hdr test_req = {
  92         .tag = cpu_to_be16(TPM_TAG_RQU_COMMAND),
  93         .len = cpu_to_be32(sizeof(test_req)),
  94         .ordinal = cpu_to_be32(TPM_ORD_GetTicks),
  95     };
  96
  97     const struct tpm_req_hdr test_req_tpm2 = {
  98         .tag = cpu_to_be16(TPM2_ST_NO_SESSIONS),
  99         .len = cpu_to_be32(sizeof(test_req_tpm2)),
 100         .ordinal = cpu_to_be32(TPM2_CC_ReadClock),
 101     };
 102     uint16_t return_tag;
 103     int ret;
 104
 105     /* Send TPM 2 command */
 106     ret = tpm_util_test(tpm_fd, (unsigned char *)&test_req_tpm2,
 107                         sizeof(test_req_tpm2), &return_tag);
 108     /* TPM 2 would respond with a tag of TPM2_ST_NO_SESSIONS */
 109     if (!ret && return_tag == TPM2_ST_NO_SESSIONS) {
 110         *tpm_version = TPM_VERSION_2_0;
 111         return 0;
 112     }
 113
 114     /* Send TPM 1.2 command */
 115     ret = tpm_util_test(tpm_fd, (unsigned char *)&test_req,
 116                         sizeof(test_req), &return_tag);
 117     if (!ret && return_tag == TPM_TAG_RSP_COMMAND) {
 118         *tpm_version = TPM_VERSION_1_2;
 119         /* this is a TPM 1.2 */
 120         return 0;
 121     }
 122
 123     *tpm_version = TPM_VERSION_UNSPEC;
 124
 125     return 1;
 126 }