event_log.c

/*
 * Copyright (C) 2020 3mdeb Embedded Systems Consulting
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

#include <boot.h>
#include <sha1sum.h>
#include <sha256.h>
#include <slrt.h>
#include <string.h>
#include "tpmlib/tpm.h"
#include "tpmlib/tpm2_constants.h"

static u8 *evtlog_base;
static u8 *ptr_current;
static u8 *limit;

#define HAS_ENOUGH_SPACE(n)      ((limit - ptr_current) > (n))

static int log_write(const void *data, unsigned size)
{
    if ( size >= limit - ptr_current )
        return 1;

    memcpy(ptr_current, data, size);
    ptr_current += size;
    return 0;
}

#define EV_NO_ACTION    0x3
#define EV_TYPE_SLAUNCH 0x502

#define HASH_COUNT 2

/* For compatibility with TXT and easier operations */

#define TPM12_EVTLOG_SIGNATURE "TXT Event Container"

typedef struct __packed {
    char signature[20];
    char reserved[12];
    u8 container_ver_major;
    u8 container_ver_minor;
    u8 pcr_event_ver_major;
    u8 pcr_event_ver_minor;
    u32 container_size;
    u32 pcr_events_offset;
    u32 next_event_offset;
    /* PCREvents[] */
} tpm12_event_log_header;

typedef struct __packed {
    u64 phys_addr;
    u32 allocated_event_container_size;
    u32 first_record_offset;
    u32 next_record_offset;
} txt_event_log_pointer2_1_element;

/* Event log headers */

typedef struct __packed {
    char signature[16];
    u32  platform_class;
    u8   spec_ver_minor;
    u8   spec_ver_major;
    u8   errata;
    u8   uintn_size;        /* reserved (must be 0) for 1.21 */
} common_spec_id_ev_t;

typedef struct __packed {
    common_spec_id_ev_t c;
    u8   vendor_info_size;
    tpm12_event_log_header hdr;             /* AKA u8 vendor_info[]; */
} tpm12_spec_id_ev_t;

typedef struct __packed {
    u32  number_of_algorithms;
    /* Hardcode table size so we can use sizeof */
    struct {
        u16  id;
        u16  size;
    } digest_sizes[HASH_COUNT];
} tpm20_digest_sizes_t;

typedef struct __packed {
    common_spec_id_ev_t c;
    tpm20_digest_sizes_t sizes;
    u8   vendor_info_size;
    txt_event_log_pointer2_1_element el;    /* AKA u8 vendor_info[]; */
} tpm20_spec_id_ev_t;

/* Event log entries */

typedef struct __packed {
    u32 pcr;
    u32 event_type;
    u8  digest[SHA1_DIGEST_SIZE];
    u32 event_size;
    /* u8 event[]; */
} tpm12_event_t;

/* The same as TPML_DIGEST_VALUES but little endian, as event log expects it */
typedef struct __packed {
    u32 count;
    u16 sha1_id;
    u8 sha1_hash[SHA1_DIGEST_SIZE];
    u16 sha256_id;
    u8 sha256_hash[SHA256_DIGEST_SIZE];
} ev_log_hash_t;

typedef struct __packed {
    u32 pcr;
    u32 event_type;
    ev_log_hash_t digests;
    u32 event_size;
    /* u8 event[]; */
} tpm20_event_t;

static const tpm12_spec_id_ev_t tpm12_id_struct = {
    .c.signature = "Spec ID Event00",
    .c.spec_ver_minor = 2,
    .c.spec_ver_major = 1,
    .c.errata = 1,
    .vendor_info_size = sizeof(tpm12_event_log_header),
    .hdr.signature = TPM12_EVTLOG_SIGNATURE,
    .hdr.container_ver_major = 1,
    .hdr.container_ver_minor = 0,
    .hdr.pcr_event_ver_major = 1,
    .hdr.pcr_event_ver_minor = 0,
    /*
     * HACK: this offset should be relative to the base of Event Log, but TXT
     * creates its log starting with the .hdr.signature, not .c.signature.
     * Linux kernel sets its evtlog_base to the address of the former one in
     * order to use the same code for both of the supported CPU vendors.
     */
    .hdr.pcr_events_offset = sizeof(tpm12_event_log_header),
    .hdr.next_event_offset = sizeof(tpm12_event_log_header)
};

static const tpm20_spec_id_ev_t tpm20_id_struct = {
    .c.signature = "Spec ID Event03",
    .c.spec_ver_minor = 0,
    .c.spec_ver_major = 2,
    .c.errata = 0,
    .c.uintn_size = 2,
    .sizes.number_of_algorithms = HASH_COUNT,
    .sizes.digest_sizes[0].id = TPM_ALG_SHA1,
    .sizes.digest_sizes[0].size = 20,
    .sizes.digest_sizes[1].id = TPM_ALG_SHA256,
    .sizes.digest_sizes[1].size = 32,
    .vendor_info_size = sizeof(txt_event_log_pointer2_1_element),
    .el.first_record_offset = 0,
    .el.next_record_offset = sizeof(tpm20_spec_id_ev_t) + sizeof(tpm12_event_t)
};

int log_event_tpm12(u32 pcr, u8 sha1[SHA1_DIGEST_SIZE], char *event)
{
    tpm12_event_t ev;
    tpm12_spec_id_ev_t *base = (tpm12_spec_id_ev_t *)
                                (evtlog_base + sizeof(tpm12_event_t));

    ev.event_size = strlen(event);

    if ( HAS_ENOUGH_SPACE(sizeof(ev) + ev.event_size) )
    {
        ev.pcr = pcr;
        ev.event_type = EV_TYPE_SLAUNCH;
        memcpy(ev.digest, sha1, 20);
        base->hdr.next_event_offset += sizeof(ev) + ev.event_size;
        log_write(&ev, sizeof(ev));
        return log_write(event, ev.event_size);
    }

    return 1;
}

int log_event_tpm20(u32 pcr, u8 sha1[SHA1_DIGEST_SIZE],
                    u8 sha256[SHA256_DIGEST_SIZE], char *event)
{
    tpm20_event_t ev;
    tpm20_spec_id_ev_t *base = (tpm20_spec_id_ev_t *)
                                (evtlog_base + sizeof(tpm12_event_t));

    ev.event_size = strlen(event);

    if ( HAS_ENOUGH_SPACE(sizeof(ev) + ev.event_size) )
    {
        ev.pcr = pcr;
        ev.event_type = EV_TYPE_SLAUNCH;
        ev.digests.count = 2;
        ev.digests.sha1_id = TPM_ALG_SHA1;
        memcpy(ev.digests.sha1_hash, sha1, 20);
        ev.digests.sha256_id = TPM_ALG_SHA256;
        memcpy(ev.digests.sha256_hash, sha256, 32);
        base->el.next_record_offset += sizeof(ev) + ev.event_size;
        log_write(&ev, sizeof(ev));
        return log_write(event, ev.event_size);
    }

    return 1;
}

int event_log_init(struct tpm *tpm)
{
    unsigned int min_size;
    struct slr_entry_log_info *info;
    u8 hash[SHA1_DIGEST_SIZE];

    info = next_entry_with_tag(NULL, SLR_ENTRY_LOG_INFO);

    if ( info == NULL || next_entry_with_tag(info, SLR_ENTRY_LOG_INFO) != NULL )
        goto err;

    min_size = sizeof (tpm12_event_t);

    if ( tpm->family == TPM12 )
    {
        min_size += sizeof(tpm12_id_struct);
        min_size += 2 * sizeof(tpm12_event_t); /* SKL and kernel hashes */
    }
    else if ( tpm->family == TPM20 )
    {
        min_size += sizeof(tpm20_id_struct);
        min_size += 2 * sizeof(tpm20_event_t); /* SKL and kernel hashes */
    }
    else
    {
        goto err;
    }

    /* Note that min_size does not include tpmXX_event_t.event[] entries */
    if ( info->size < min_size )
        goto err;

    ptr_current = evtlog_base = _p(info->addr);
    limit = _p(info->addr + info->size);

    /* Check for overflow */
    if ( ptr_current > limit )
        goto err;

    /*
     * Bootloader controls location and size, so it could force SKL to overwrite
     * its code **after** it was measured. Make sure that the Event Log and SKL
     * do not overlap before wiping the memory.
     */
    if ( !(_p(limit) < _p(_start) || _p(_start + SLB_SIZE) < _p(ptr_current)) )
        goto err;

    memset(ptr_current, 0, info->size);

    /* Check if log format matches TPM family */
    if ((tpm->family == TPM12 && info->format != SLR_LOG_FORMAT_TPM12_TXT) ||
        (tpm->family == TPM20 && info->format != SLR_LOG_FORMAT_TPM20_TCG))
        goto err;

    /* Write log header */
    {
        tpm12_event_t ev;

        ev.pcr = 0;
        ev.event_type = EV_NO_ACTION;
        memset(ev.digest, 0, 20);
        if ( tpm->family == TPM12 )
            ev.event_size = sizeof(tpm12_id_struct);
        else
            ev.event_size = sizeof(tpm20_id_struct);

        log_write(&ev, sizeof(ev));
    }

    /* Sizes were checked earlier so log_write() won't fail here */
    if ( tpm->family == TPM12 ) {
        tpm12_spec_id_ev_t *id = (tpm12_spec_id_ev_t *)ptr_current;
        log_write(&tpm12_id_struct, sizeof(tpm12_id_struct));
        id->hdr.container_size = info->size;
    } else {
        tpm20_spec_id_ev_t *id = (tpm20_spec_id_ev_t *)ptr_current;
        log_write(&tpm20_id_struct, sizeof(tpm20_id_struct));
        id->el.allocated_event_container_size = info->size;
        id->el.phys_addr = _u(evtlog_base);
    }

    /* Log what was done by SKINIT */
    sha1sum(hash, _start, _end_of_measured - _start);
    if ( tpm->family == TPM12 )
    {
        return log_event_tpm12(17, hash, "SKINIT");
    }
    else if ( tpm->family == TPM20 )
    {
        u8 sha256_hash[SHA256_DIGEST_SIZE];

        sha256sum(sha256_hash, _start, _end_of_measured - _start);
        return log_event_tpm20(17, hash, sha256_hash, "SKINIT");
    }

err:
    /* Make sure that further calls to log_write() will fail */
    limit = ptr_current;
    return 1;
}