tpm_common.c

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/* SPDX-License-Identifier: GPL-2.0-only */
 
#include <security/tpm/tspi.h>
#include <vb2_api.h>
#include <security/vboot/tpm_common.h>
 
#define TPM_PCR_BOOT_MODE "VBOOT: boot mode"
#define TPM_PCR_GBB_HWID_NAME "VBOOT: GBB HWID"
 
uint32_t vboot_setup_tpm(struct vb2_context *ctx)
{
        uint32_t result;
 
        result = tpm_setup(ctx->flags & VB2_CONTEXT_S3_RESUME);
        if (result == TPM_E_MUST_REBOOT)
                ctx->flags |= VB2_CONTEXT_SECDATA_WANTS_REBOOT;
 
        return result;
}
 
vb2_error_t vboot_extend_pcr(struct vb2_context *ctx, int pcr,
                             enum vb2_pcr_digest which_digest)
{
        uint8_t buffer[VB2_PCR_DIGEST_RECOMMENDED_SIZE];
        uint32_t size = sizeof(buffer);
        vb2_error_t rv;
 
        rv = vb2api_get_pcr_digest(ctx, which_digest, buffer, &size);
        if (rv != VB2_SUCCESS)
                return rv;
        if (size < TPM_PCR_MINIMUM_DIGEST_SIZE)
                return VB2_ERROR_UNKNOWN;
 
        /*
         * On TPM 1.2, all PCRs are intended for use with SHA1. We truncate our
         * SHA256 HWID hash to 20 bytes to make it fit. On TPM 2.0, we always
         * want to use the SHA256 banks, even for the boot mode which is
         * technically a SHA1 value for historical reasons. vboot has already
         * zero-extended the buffer to 32 bytes for us, so we just take it like
         * that and pretend it's a SHA256. In practice, this means we never care
         * about the (*size) value returned from vboot (which indicates how many
         * significant bytes vboot wrote, although it always extends zeroes up
         * to the end of the buffer), we always use a hardcoded size instead.
         */
        _Static_assert(sizeof(buffer) >= VB2_SHA256_DIGEST_SIZE,
                       "Buffer needs to be able to fit at least a SHA256");
        enum vb2_hash_algorithm algo = CONFIG(TPM1) ? VB2_HASH_SHA1 : VB2_HASH_SHA256;
 
        switch (which_digest) {
        /* SHA1 of (devmode|recmode|keyblock) bits */
        case BOOT_MODE_PCR:
                return tpm_extend_pcr(pcr, algo, buffer, vb2_digest_size(algo),
                                      TPM_PCR_BOOT_MODE);
         /* SHA256 of HWID */
        case HWID_DIGEST_PCR:
                return tpm_extend_pcr(pcr, algo, buffer, vb2_digest_size(algo),
                                      TPM_PCR_GBB_HWID_NAME);
        default:
                return VB2_ERROR_UNKNOWN;
        }
}