src/security/intel/txt/romstage.c

/* SPDX-License-Identifier: GPL-2.0-only */

#include <arch/mmio.h>
#include <cf9_reset.h>
#include <console/console.h>
#include <cpu/intel/common/common.h>
#include <cpu/x86/msr.h>
#include <southbridge/intel/common/pmbase.h>
#include <timer.h>
#include <types.h>

#include <security/tpm/tis.h>

#include "txt.h"
#include "txt_register.h"
#include "txt_getsec.h"

static bool is_establishment_bit_asserted(void)
{
	struct stopwatch timer;
	uint8_t access;

	/* Spec says no less than 30 milliseconds */
	stopwatch_init_msecs_expire(&timer, 50);

	while (true) {
		access = read8((void *)TPM_ACCESS_REG);

		/* Register returns all ones if TPM is missing */
		if (access == 0xff)
			return false;

		if (access & TPM_ACCESS_VALID)
			break;

		/* On timeout, assume that the TPM is not working */
		if (stopwatch_expired(&timer))
			return false;
	}

	/* This bit uses inverted logic: if cleared, establishment is asserted */
	return !(access & TPM_ACCESS_ESTABLISHMENT);
}

static bool is_txt_cpu(void)
{
	const uint32_t ecx = cpu_get_feature_flags_ecx();

	return (ecx & (CPUID_SMX | CPUID_VMX)) == (CPUID_SMX | CPUID_VMX);
}

static bool is_txt_chipset(void)
{
	uint32_t eax;

	const bool success = getsec_capabilities(&eax);

	return success && eax & 1;
}

/* Print the bad news */
static void print_memory_is_locked(void)
{
	if (!CONFIG(INTEL_TXT_LOGGING))
		return;

	printk(BIOS_EMERG, "FATAL: Cannot run SCLEAN. Memory will remain locked.\n");
	printk(BIOS_EMERG, "\n");
	printk(BIOS_EMERG, "If you still want to boot, your options are:\n");
	printk(BIOS_EMERG, "\n");
	printk(BIOS_EMERG, "   1. Flash a coreboot image with a valid BIOS ACM.\n");
	printk(BIOS_EMERG, "      Then, try again and hope it works this time.\n");
	printk(BIOS_EMERG, "\n");
	printk(BIOS_EMERG, "   2. If possible, remove the TPM from the system.\n");
	printk(BIOS_EMERG, "      Reinstalling the TPM might lock memory again.\n");
	printk(BIOS_EMERG, "\n");
	printk(BIOS_EMERG, "   3. Disconnect all power sources, and RTC battery.\n");
	printk(BIOS_EMERG, "      This may not work on all TXT-enabled platforms.\n");
	printk(BIOS_EMERG, "\n");
}

void intel_txt_romstage_init(void)
{
	/* Bail early if the CPU doesn't support TXT */
	if (!is_txt_cpu())
		return;

	/* We need to use GETSEC here, so enable it */
	enable_getsec_or_reset();

	if (!is_txt_chipset())
		return;

	const uint8_t txt_ests = read8((void *)TXT_ESTS);

	const bool establishment = is_establishment_bit_asserted();
	const bool is_wake_error = !!(txt_ests & TXT_ESTS_WAKE_ERROR_STS);

	if (CONFIG(INTEL_TXT_LOGGING)) {

		printk(BIOS_INFO, "TEE-TXT: TPM established: %s\n",
		       establishment ? "true" : "false");
	}

	if (establishment && is_wake_error) {

		printk(BIOS_ERR, "TEE-TXT: Secrets remain in memory. SCLEAN is required.\n");

		if (txt_ests & TXT_ESTS_TXT_RESET_STS) {
			printk(BIOS_ERR, "TEE-TXT: TXT_RESET bit set, doing full reset!\n");
			full_reset();
		}

		/* FIXME: Clear SLP_TYP# */
		write_pmbase32(4, read_pmbase32(4) & ~(0x7 << 10));

		intel_txt_run_sclean();

		/* If running the BIOS ACM is impossible, manual intervention is required */
		print_memory_is_locked();

		/* FIXME: vboot A/B could be used to recover, but has not been tested */
		die("Could not execute BIOS ACM to unlock the memory.\n");
	}
}