hw/tpm/tpm_util.c

/*
 * TPM utility functions
 *
 *  Copyright (c) 2010 - 2015 IBM Corporation
 *  Authors:
 *    Stefan Berger <stefanb@us.ibm.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, see <http://www.gnu.org/licenses/>
 */

#include "tpm_util.h"
#include "tpm_int.h"

/*
 * A basic test of a TPM device. We expect a well formatted response header
 * (error response is fine) within one second.
 */
static int tpm_util_test(int fd,
                         unsigned char *request,
                         size_t requestlen,
                         uint16_t *return_tag)
{
    struct tpm_resp_hdr *resp;
    fd_set readfds;
    int n;
    struct timeval tv = {
        .tv_sec = 1,
        .tv_usec = 0,
    };
    unsigned char buf[1024];

    n = write(fd, request, requestlen);
    if (n < 0) {
        return errno;
    }
    if (n != requestlen) {
        return EFAULT;
    }

    FD_ZERO(&readfds);
    FD_SET(fd, &readfds);

    /* wait for a second */
    n = select(fd + 1, &readfds, NULL, NULL, &tv);
    if (n != 1) {
        return errno;
    }

    n = read(fd, &buf, sizeof(buf));
    if (n < sizeof(struct tpm_resp_hdr)) {
        return EFAULT;
    }

    resp = (struct tpm_resp_hdr *)buf;
    /* check the header */
    if (be32_to_cpu(resp->len) != n) {
        return EBADMSG;
    }

    *return_tag = be16_to_cpu(resp->tag);

    return 0;
}

/*
 * Probe for the TPM device in the back
 * Returns 0 on success with the version of the probed TPM set, 1 on failure.
 */
int tpm_util_test_tpmdev(int tpm_fd, TPMVersion *tpm_version)
{
    /*
     * Sending a TPM1.2 command to a TPM2 should return a TPM1.2
     * header (tag = 0xc4) and error code (TPM_BADTAG = 0x1e)
     *
     * Sending a TPM2 command to a TPM 2 will give a TPM 2 tag in the
     * header.
     * Sending a TPM2 command to a TPM 1.2 will give a TPM 1.2 tag
     * in the header and an error code.
     */
    const struct tpm_req_hdr test_req = {
        .tag = cpu_to_be16(TPM_TAG_RQU_COMMAND),
        .len = cpu_to_be32(sizeof(test_req)),
        .ordinal = cpu_to_be32(TPM_ORD_GetTicks),
    };

    const struct tpm_req_hdr test_req_tpm2 = {
        .tag = cpu_to_be16(TPM2_ST_NO_SESSIONS),
        .len = cpu_to_be32(sizeof(test_req_tpm2)),
        .ordinal = cpu_to_be32(TPM2_CC_ReadClock),
    };
    uint16_t return_tag;
    int ret;

    /* Send TPM 2 command */
    ret = tpm_util_test(tpm_fd, (unsigned char *)&test_req_tpm2,
                        sizeof(test_req_tpm2), &return_tag);
    /* TPM 2 would respond with a tag of TPM2_ST_NO_SESSIONS */
    if (!ret && return_tag == TPM2_ST_NO_SESSIONS) {
        *tpm_version = TPM_VERSION_2_0;
        return 0;
    }

    /* Send TPM 1.2 command */
    ret = tpm_util_test(tpm_fd, (unsigned char *)&test_req,
                        sizeof(test_req), &return_tag);
    if (!ret && return_tag == TPM_TAG_RSP_COMMAND) {
        *tpm_version = TPM_VERSION_1_2;
        /* this is a TPM 1.2 */
        return 0;
    }

    *tpm_version = TPM_VERSION_UNSPEC;

    return 1;
}