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 "qemu/osdep.h"
  23 #include "tpm_util.h"
  24 #include "tpm_int.h"
  25
  26 /*
  27  * A basic test of a TPM device. We expect a well formatted response header
  28  * (error response is fine) within one second.
  29  */
  30 static int tpm_util_test(int fd,
  31                          unsigned char *request,
  32                          size_t requestlen,
  33                          uint16_t *return_tag)
  34 {
  35     struct tpm_resp_hdr *resp;
  36     fd_set readfds;
  37     int n;
  38     struct timeval tv = {
  39         .tv_sec = 1,
  40         .tv_usec = 0,
  41     };
  42     unsigned char buf[1024];
  43
  44     n = write(fd, request, requestlen);
  45     if (n < 0) {
  46         return errno;
  47     }
  48     if (n != requestlen) {
  49         return EFAULT;
  50     }
  51
  52     FD_ZERO(&readfds);
  53     FD_SET(fd, &readfds);
  54
  55     /* wait for a second */
  56     n = select(fd + 1, &readfds, NULL, NULL, &tv);
  57     if (n != 1) {
  58         return errno;
  59     }
  60
  61     n = read(fd, &buf, sizeof(buf));
  62     if (n < sizeof(struct tpm_resp_hdr)) {
  63         return EFAULT;
  64     }
  65
  66     resp = (struct tpm_resp_hdr *)buf;
  67     /* check the header */
  68     if (be32_to_cpu(resp->len) != n) {
  69         return EBADMSG;
  70     }
  71
  72     *return_tag = be16_to_cpu(resp->tag);
  73
  74     return 0;
  75 }
  76
  77 /*
  78  * Probe for the TPM device in the back
  79  * Returns 0 on success with the version of the probed TPM set, 1 on failure.
  80  */
  81 int tpm_util_test_tpmdev(int tpm_fd, TPMVersion *tpm_version)
  82 {
  83     /*
  84      * Sending a TPM1.2 command to a TPM2 should return a TPM1.2
  85      * header (tag = 0xc4) and error code (TPM_BADTAG = 0x1e)
  86      *
  87      * Sending a TPM2 command to a TPM 2 will give a TPM 2 tag in the
  88      * header.
  89      * Sending a TPM2 command to a TPM 1.2 will give a TPM 1.2 tag
  90      * in the header and an error code.
  91      */
  92     const struct tpm_req_hdr test_req = {
  93         .tag = cpu_to_be16(TPM_TAG_RQU_COMMAND),
  94         .len = cpu_to_be32(sizeof(test_req)),
  95         .ordinal = cpu_to_be32(TPM_ORD_GetTicks),
  96     };
  97
  98     const struct tpm_req_hdr test_req_tpm2 = {
  99         .tag = cpu_to_be16(TPM2_ST_NO_SESSIONS),
 100         .len = cpu_to_be32(sizeof(test_req_tpm2)),
 101         .ordinal = cpu_to_be32(TPM2_CC_ReadClock),
 102     };
 103     uint16_t return_tag;
 104     int ret;
 105
 106     /* Send TPM 2 command */
 107     ret = tpm_util_test(tpm_fd, (unsigned char *)&test_req_tpm2,
 108                         sizeof(test_req_tpm2), &return_tag);
 109     /* TPM 2 would respond with a tag of TPM2_ST_NO_SESSIONS */
 110     if (!ret && return_tag == TPM2_ST_NO_SESSIONS) {
 111         *tpm_version = TPM_VERSION_2_0;
 112         return 0;
 113     }
 114
 115     /* Send TPM 1.2 command */
 116     ret = tpm_util_test(tpm_fd, (unsigned char *)&test_req,
 117                         sizeof(test_req), &return_tag);
 118     if (!ret && return_tag == TPM_TAG_RSP_COMMAND) {
 119         *tpm_version = TPM_VERSION_1_2;
 120         /* this is a TPM 1.2 */
 121         return 0;
 122     }
 123
 124     *tpm_version = TPM_VERSION_UNSPEC;
 125
 126     return 1;
 127 }