romstage.c

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/* SPDX-License-Identifier: GPL-2.0-only */
 
#include <arch/cpu.h>
#include <arch/mmio.h>
#include <cf9_reset.h>
#include <console/console.h>
#include <cpu/intel/common/common.h>
#include <cpu/x86/cr.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()) {
                printk(BIOS_ERR, "TEE-TXT: CPU not TXT capable.\n");
                return;
        }
 
        /*
         * We need to use GETSEC here, so enable it.
         * CR4_SMXE is all we need to be able to call GETSEC[CAPABILITIES]
         * or GETSEC[ENTERACCS] for SCLEAN.
         */
        write_cr4(read_cr4() | CR4_SMXE);
 
        if (!is_txt_chipset()) {
                printk(BIOS_ERR, "TEE-TXT: Chipset not TXT capable.\n");
                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 global reset!\n");
                        txt_reset_platform();
                }
 
                /* 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");
        }
}