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: [email protected] # 6.1.y+
Fixes: b006c43 ("hwrng: core - start hwrng kthread also for untrusted sources")
Fixes: f1324bb ("tpm: disable hwrng for fTPM on some AMD designs")
Reported-by: [email protected]
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217719
Reported-by: [email protected]
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217212
Signed-off-by: Mario Limonciello <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
Signed-off-by: Jarkko Sakkinen <[email protected]>

Author: superm1

drivers/char/tpm/tpm-chip.c

@@ -510,70 +510,6 @@ static int tpm_add_legacy_sysfs(struct tpm_chip *chip)
 	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);
@@ -588,7 +524,7 @@ static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 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),
@@ -719,7 +655,7 @@ void tpm_chip_unregister(struct tpm_chip *chip)
 {
 	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

@@ -463,6 +463,28 @@ static bool crb_req_canceled(struct tpm_chip *chip, u8 status)
 	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,
@@ -800,6 +822,14 @@ static int crb_acpi_add(struct acpi_device *device)
 	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);
 
 out:

include/linux/tpm.h

@@ -283,6 +283,7 @@ enum tpm_chip_flags {
 	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)