tpm: Disable RNG for all AMD fTPMs

The TPM RNG functionality is not necessary for entropy when the CPU
already supports the RDRAND instruction. The TPM RNG functionality
was previously disabled on a subset of AMD fTPM series, but reports
continue to show problems on some systems causing stutter root caused
to TPM RNG functionality.

Expand disabling TPM RNG use for all AMD fTPMs whether they have versions
that claim to have fixed or not. To accomplish this, move the detection
into part of the TPM CRB registration and add a flag indicating that
the TPM should opt-out of registration to hwrng.

Cc: [e-mail] # 6.1.y+
Fixes: b006c439d58d ("hwrng: core - start hwrng kthread also for untrusted sources")
Fixes: f1324bbc4011 ("tpm: disable hwrng for fTPM on some AMD designs")
Reported-by: [e-mail]
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217719
Reported-by: [e-mail]
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217212
Signed-off-by: Mario Limonciello <[e-mail]>
Reviewed-by: Jarkko Sakkinen <[e-mail]>
Signed-off-by: Jarkko Sakkinen <[e-mail]>

drivers/char/tpm/tpm-chip.c

···
 	return 0;
 }
 
-/*
- * Some AMD fTPM versions may cause stutter
- * https://www.amd.com/en/support/kb/faq/pa-410
- *
- * Fixes are available in two series of fTPM firmware:
- * 6.x.y.z series: 6.0.18.6 +
- * 3.x.y.z series: 3.57.y.5 +
- */
-#ifdef CONFIG_X86
-static bool tpm_amd_is_rng_defective(struct tpm_chip *chip)
-{
-	u32 val1, val2;
-	u64 version;
-	int ret;
-
-	if (!(chip->flags & TPM_CHIP_FLAG_TPM2))
-		return false;
-
-	ret = tpm_request_locality(chip);
-	if (ret)
-		return false;
-
-	ret = tpm2_get_tpm_pt(chip, TPM2_PT_MANUFACTURER, &val1, NULL);
-	if (ret)
-		goto release;
-	if (val1 != 0x414D4400U /* AMD */) {
-		ret = -ENODEV;
-		goto release;
-	}
-	ret = tpm2_get_tpm_pt(chip, TPM2_PT_FIRMWARE_VERSION_1, &val1, NULL);
-	if (ret)
-		goto release;
-	ret = tpm2_get_tpm_pt(chip, TPM2_PT_FIRMWARE_VERSION_2, &val2, NULL);
-
-release:
-	tpm_relinquish_locality(chip);
-
-	if (ret)
-		return false;
-
-	version = ((u64)val1 << 32) | val2;
-	if ((version >> 48) == 6) {
-		if (version >= 0x0006000000180006ULL)
-			return false;
-	} else if ((version >> 48) == 3) {
-		if (version >= 0x0003005700000005ULL)
-			return false;
-	} else {
-		return false;
-	}
-
-	dev_warn(&chip->dev,
-		 "AMD fTPM version 0x%llx causes system stutter; hwrng disabled\n",
-		 version);
-
-	return true;
-}
-#else
-static inline bool tpm_amd_is_rng_defective(struct tpm_chip *chip)
-{
-	return false;
-}
-#endif /* CONFIG_X86 */
-
 static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 {
 	struct tpm_chip *chip = container_of(rng, struct tpm_chip, hwrng);
···
 static int tpm_add_hwrng(struct tpm_chip *chip)
 {
 	if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM) || tpm_is_firmware_upgrade(chip) ||
-	    tpm_amd_is_rng_defective(chip))
+	    chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED)
 		return 0;
 
 	snprintf(chip->hwrng_name, sizeof(chip->hwrng_name),
···
 {
 	tpm_del_legacy_sysfs(chip);
 	if (IS_ENABLED(CONFIG_HW_RANDOM_TPM) && !tpm_is_firmware_upgrade(chip) &&
-	    !tpm_amd_is_rng_defective(chip))
+	    !(chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED))
 		hwrng_unregister(&chip->hwrng);
 	tpm_bios_log_teardown(chip);
 	if (chip->flags & TPM_CHIP_FLAG_TPM2 && !tpm_is_firmware_upgrade(chip))

drivers/char/tpm/tpm_crb.c

···
 	return (cancel & CRB_CANCEL_INVOKE) == CRB_CANCEL_INVOKE;
 }
 
+static int crb_check_flags(struct tpm_chip *chip)
+{
+	u32 val;
+	int ret;
+
+	ret = crb_request_locality(chip, 0);
+	if (ret)
+		return ret;
+
+	ret = tpm2_get_tpm_pt(chip, TPM2_PT_MANUFACTURER, &val, NULL);
+	if (ret)
+		goto release;
+
+	if (val == 0x414D4400U /* AMD */)
+		chip->flags |= TPM_CHIP_FLAG_HWRNG_DISABLED;
+
+release:
+	crb_relinquish_locality(chip, 0);
+
+	return ret;
+}
+
 static const struct tpm_class_ops tpm_crb = {
 	.flags = TPM_OPS_AUTO_STARTUP,
 	.status = crb_status,
···
 	dev_set_drvdata(&chip->dev, priv);
 	chip->acpi_dev_handle = device->handle;
 	chip->flags = TPM_CHIP_FLAG_TPM2;
+
+	rc = tpm_chip_bootstrap(chip);
+	if (rc)
+		goto out;
+
+	rc = crb_check_flags(chip);
+	if (rc)
+		goto out;
 
 	rc = tpm_chip_register(chip);
 

include/linux/tpm.h

···
 	TPM_CHIP_FLAG_FIRMWARE_POWER_MANAGED	= BIT(6),
 	TPM_CHIP_FLAG_FIRMWARE_UPGRADE		= BIT(7),
 	TPM_CHIP_FLAG_SUSPENDED			= BIT(8),
+	TPM_CHIP_FLAG_HWRNG_DISABLED		= BIT(9),
 };
 
 #define to_tpm_chip(d) container_of(d, struct tpm_chip, dev)