tpm: Enable hwrng only for Pluton on AMD CPUs

The vendor check introduced by commit 554b841d4703 ("tpm: Disable RNG for all AMD fTPMs") doesn't work properly on a number of Intel fTPMs. On the reported systems the TPM doesn't reply at bootup and returns back the command code. This makes the TPM fail probe.

Since only Microsoft Pluton is the only known combination of AMD CPU and fTPM from other vendor, disable hwrng otherwise. In order to make sysadmin aware of this, print also info message to the klog.

Cc [email protected]

Fixes 554b841d4703 ("tpm: Disable RNG for all AMD fTPMs")

Reported-by Todd Brandt <[email protected]>

Closes https://bugzilla.kernel.org/show_bug.cgi?id=217804

Signed-off-by Jarkko Sakkinen <[email protected]>

---
v2:
* CONFIG_X86

* Removed "Reviewed-by: Jarkko Sakkinen <[email protected]>"
* Removed "Signed-off-by: Mario Limonciello <[email protected]>"

---
 drivers/char/tpm/tpm_crb.c | 31 ++++++-------------------------
 1 file changed, 6 insertions(+), 25 deletions(-)

drivers/char/tpm/tpm_crb.c +6 -25

index 65ff4d2fbe8d..28448bfd4062 100644
@@ -463,28 +463,6 @@ 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,

@@ -827,9 +805,12 @@ static int crb_acpi_add(struct acpi_device *device)
 	if (rc)
 		goto out;
 
-	rc = crb_check_flags(chip);
-	if (rc)
-		goto out;
+	/* A quirk for https://www.amd.com/en/support/kb/faq/pa-410 */
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
+	    priv->sm != ACPI_TPM2_COMMAND_BUFFER_WITH_PLUTON) {
+		dev_info(dev, "Disabling hwrng\n");
+		chip->flags |= TPM_CHIP_FLAG_HWRNG_DISABLED;
+	}
 
 	rc = tpm_chip_register(chip);
 

Signature · 1 line

2.39.2

Quoted 9 lines · Jarkko Sakkinen

The vendor check introduced by commit 554b841d4703 ("tpm: Disable RNG for all AMD fTPMs") doesn't work properly on a number of Intel fTPMs. On the reported systems the TPM doesn't reply at bootup and returns back the command code. This makes the TPM fail probe.

Since only Microsoft Pluton is the only known combination of AMD CPU and fTPM from other vendor, disable hwrng otherwise. In order to make sysadmin aware of this, print also info message to the klog.

Quoted 8 lines

Cc [email protected]

Fixes 554b841d4703 ("tpm: Disable RNG for all AMD fTPMs")

Reported-by Todd Brandt <[email protected]>

Closes https://bugzilla.kernel.org/show_bug.cgi?id=217804

Signed-off-by Jarkko Sakkinen <[email protected]>

---
v2:
* CONFIG_X86

Did you mean to wrap the crb_acpi_add chunk with CONFIG_X86?