security/intel/txt: Create Intel TXT lib with helper functions

This patch decouples useful TXT related operations from the romstage.c
file alone and moves them into a helper txtlib.c. This effort will be
helpful for SoC users to perform TXT related operations
(like Disabling TXT) even without selecting INTEL_TXT config.

At present, those helper functions are only available upon selecting
INTEL_TXT which is not getting enabled for most of the SoC platform in
the scope of the Chromebooks.

TEST=Able to access functions from txtlib.c even without selecting
INTEL_TXT config.

Signed-off-by: Subrata Banik <subratabanik@google.com>
Change-Id: Iff5b4e705e18cbaf181b4c71bfed368c3ed047ed
Reviewed-on: https://review.coreboot.org/c/coreboot/+/71573
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tarun Tuli <taruntuli@google.com>
Reviewed-by: Sridhar Siricilla <sridhar.siricilla@intel.com>

src/security/intel/txt/Kconfig

@@ -1,8 +1,17 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
+config INTEL_TXT_LIB
+	bool
+	default n
+	help
+	  This option includes library functions related to the TXT
+	  operation which SoC would still like to access without enabling
+	  INTEL_TXT config.
+
 config INTEL_TXT
 	bool "Intel TXT support"
 	default n
+	select INTEL_TXT_LIB
 	select MRC_SETTINGS_PROTECT if CACHE_MRC_SETTINGS
 	select ENABLE_VMX if CPU_INTEL_COMMON
 	select AP_IN_SIPI_WAIT

src/security/intel/txt/Makefile.inc

@@ -1,3 +1,5 @@
+romstage-$(CONFIG_INTEL_TXT_LIB) += txtlib.c
+
 ifeq ($(CONFIG_INTEL_TXT),y)
 
 all-y += logging.c

src/security/intel/txt/romstage.c

@@ -4,52 +4,15 @@
 #include <console/console.h>
 #include <cpu/intel/common/common.h>
 #include <cpu/x86/cr.h>
-#include <cpu/x86/msr.h>
 #include <device/mmio.h>
 #include <southbridge/intel/common/pmbase.h>
-#include <timer.h>
 #include <types.h>
 
-#include <security/tpm/tis.h>
-
 #include "txt.h"
+#include "txtlib.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;

src/security/intel/txt/txtlib.c

@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <arch/cpu.h>
+#include <cpu/intel/common/common.h>
+#include <cpu/x86/msr.h>
+#include <device/mmio.h>
+#include <security/intel/txt/txt.h>
+#include <security/tpm/tis.h>
+#include <timer.h>
+
+#include "txtlib.h"
+#include "txt_register.h"
+
+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);
+}
+
+bool is_txt_cpu(void)
+{
+	const uint32_t ecx = cpu_get_feature_flags_ecx();
+
+	return (ecx & (CPUID_SMX | CPUID_VMX)) == (CPUID_SMX | CPUID_VMX);
+}

src/security/intel/txt/txtlib.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef SECURITY_INTEL_TXT_LIB_H_
+#define SECURITY_INTEL_TXT_LIB_H_
+
+#include <types.h>
+
+bool is_establishment_bit_asserted(void);
+
+bool is_txt_cpu(void);
+
+#endif /* SECURITY_INTEL_TXT_LIB_H_ */