Re: [PATCH 1/1] tpm: disable hwrng for fTPM on some AMD designs

On Tue, Feb 14, 2023 at 02:19:55PM -0600, Mario Limonciello wrote:

AMD has issued an advisory indicating that having fTPM enabled in BIOS can cause "stuttering" in the OS. This issue has been fixed in newer versions of the fTPM firmware, but it's up to system designers to decide whether to distribute it.

This issue has existed for a while, but is more prevalent starting with kernel 6.1 because commit b006c439d58db ("hwrng: core - start hwrng kthread also for untrusted sources") started to use the fTPM for hwrng by default. However, all uses of /dev/hwrng result in unacceptable stuttering.

So, simply disable registration of the defective hwrng when detecting these faulty fTPM versions.

Link: https://www.amd.com/en/support/kb/faq/pa-410 Link: https://bugzilla.kernel.org/show_bug.cgi?id=216989 Link: https://lore.kernel.org/all/20230209153120.261904-1-Jason@zx2c4.com/ Fixes: b006c439d58d ("hwrng: core - start hwrng kthread also for untrusted sources") Cc: stable@vger.kernel.org Cc: Jarkko Sakkinen jarkko@kernel.org Cc: Thorsten Leemhuis regressions@leemhuis.info Cc: James Bottomley James.Bottomley@hansenpartnership.com Co-developed-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Mario Limonciello mario.limonciello@amd.com

---

drivers/char/tpm/tpm-chip.c | 62 ++++++++++++++++++++++++++++++- drivers/char/tpm/tpm.h | 73 +++++++++++++++++++++++++++++++++++++ 2 files changed, 134 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c index 741d8f3e8fb3a..348dd5705fbb6 100644 --- a/drivers/char/tpm/tpm-chip.c +++ b/drivers/char/tpm/tpm-chip.c @@ -512,6 +512,65 @@ static int tpm_add_legacy_sysfs(struct tpm_chip *chip) return 0; } +static bool tpm_is_rng_defective(struct tpm_chip *chip)

Perhaps tpm_amd_* ?

Also, just a question: is there any legit use for fTPM's, which are not updated? I.e. why would want tpm_crb to initialize with a dysfunctional firmware?

I.e. the existential question is: is it better to workaround the issue and let pass through, or make the user aware that the firmware would really need an update.

+{

• int ret;
• u64 version;
• u32 val1, val2;

I'd use reverse christmas tree order here.

• /* No known-broken TPM1 chips. */
• if (!(chip->flags & TPM_CHIP_FLAG_TPM2))

• return false;
  

• ret = tpm_request_locality(chip);
• if (ret)

• return false;
  

• /* Some AMD fTPM versions may cause stutter */
• 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);
• if (ret)

• goto release;
  

+release:

• tpm_relinquish_locality(chip);
• if (ret)

• return false;
  

• version = ((u64)val1 << 32) | val2;
• /*

• * Fixes for stutter as described in
  

• * https://www.amd.com/en/support/kb/faq/pa-410
  

• * are available in two series of fTPM firmware:
  

• *   6.x.y.z series: 6.0.18.6 +
  

• *   3.x.y.z series: 3.57.x.5 +
  

• */
  

• if ((version >> 48) == 6) {

• if (version >= 0x0006000000180006ULL)
  

• 	return false;
  

• } else if ((version >> 48) == 3) {

• if (version >= 0x0003005700000005ULL)
  

• 	return false;
  

• } else {

• return false;
  

• }

You can drop the curly braces here.

• dev_warn(&chip->dev,

•  "AMD fTPM version 0x%llx causes system stutter; hwrng disabled\n",
  

•  version);
  

• return true;

+}

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); @@ -521,7 +580,8 @@ 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))

• if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM) || tpm_is_firmware_upgrade(chip) ||

•    tpm_is_rng_defective(chip))
  

  return 0;

snprintf(chip->hwrng_name, sizeof(chip->hwrng_name), diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h index 24ee4e1cc452a..830014a266090 100644 --- a/drivers/char/tpm/tpm.h +++ b/drivers/char/tpm/tpm.h @@ -150,6 +150,79 @@ enum tpm_sub_capabilities { TPM_CAP_PROP_TIS_DURATION = 0x120, }; +enum tpm2_pt_props {

• TPM2_PT_NONE = 0x00000000,
• TPM2_PT_GROUP = 0x00000100,
• TPM2_PT_FIXED = TPM2_PT_GROUP * 1,
• TPM2_PT_FAMILY_INDICATOR = TPM2_PT_FIXED + 0,
• TPM2_PT_LEVEL = TPM2_PT_FIXED + 1,
• TPM2_PT_REVISION = TPM2_PT_FIXED + 2,
• TPM2_PT_DAY_OF_YEAR = TPM2_PT_FIXED + 3,
• TPM2_PT_YEAR = TPM2_PT_FIXED + 4,
• TPM2_PT_MANUFACTURER = TPM2_PT_FIXED + 5,
• TPM2_PT_VENDOR_STRING_1 = TPM2_PT_FIXED + 6,
• TPM2_PT_VENDOR_STRING_2 = TPM2_PT_FIXED + 7,
• TPM2_PT_VENDOR_STRING_3 = TPM2_PT_FIXED + 8,
• TPM2_PT_VENDOR_STRING_4 = TPM2_PT_FIXED + 9,
• TPM2_PT_VENDOR_TPM_TYPE = TPM2_PT_FIXED + 10,
• TPM2_PT_FIRMWARE_VERSION_1 = TPM2_PT_FIXED + 11,
• TPM2_PT_FIRMWARE_VERSION_2 = TPM2_PT_FIXED + 12,
• TPM2_PT_INPUT_BUFFER = TPM2_PT_FIXED + 13,
• TPM2_PT_HR_TRANSIENT_MIN = TPM2_PT_FIXED + 14,
• TPM2_PT_HR_PERSISTENT_MIN = TPM2_PT_FIXED + 15,
• TPM2_PT_HR_LOADED_MIN = TPM2_PT_FIXED + 16,
• TPM2_PT_ACTIVE_SESSIONS_MAX = TPM2_PT_FIXED + 17,
• TPM2_PT_PCR_COUNT = TPM2_PT_FIXED + 18,
• TPM2_PT_PCR_SELECT_MIN = TPM2_PT_FIXED + 19,
• TPM2_PT_CONTEXT_GAP_MAX = TPM2_PT_FIXED + 20,
• TPM2_PT_NV_COUNTERS_MAX = TPM2_PT_FIXED + 22,
• TPM2_PT_NV_INDEX_MAX = TPM2_PT_FIXED + 23,
• TPM2_PT_MEMORY = TPM2_PT_FIXED + 24,
• TPM2_PT_CLOCK_UPDATE = TPM2_PT_FIXED + 25,
• TPM2_PT_CONTEXT_HASH = TPM2_PT_FIXED + 26,
• TPM2_PT_CONTEXT_SYM = TPM2_PT_FIXED + 27,
• TPM2_PT_CONTEXT_SYM_SIZE = TPM2_PT_FIXED + 28,
• TPM2_PT_ORDERLY_COUNT = TPM2_PT_FIXED + 29,
• TPM2_PT_MAX_COMMAND_SIZE = TPM2_PT_FIXED + 30,
• TPM2_PT_MAX_RESPONSE_SIZE = TPM2_PT_FIXED + 31,
• TPM2_PT_MAX_DIGEST = TPM2_PT_FIXED + 32,
• TPM2_PT_MAX_OBJECT_CONTEXT = TPM2_PT_FIXED + 33,
• TPM2_PT_MAX_SESSION_CONTEXT = TPM2_PT_FIXED + 34,
• TPM2_PT_PS_FAMILY_INDICATOR = TPM2_PT_FIXED + 35,
• TPM2_PT_PS_LEVEL = TPM2_PT_FIXED + 36,
• TPM2_PT_PS_REVISION = TPM2_PT_FIXED + 37,
• TPM2_PT_PS_DAY_OF_YEAR = TPM2_PT_FIXED + 38,
• TPM2_PT_PS_YEAR = TPM2_PT_FIXED + 39,
• TPM2_PT_SPLIT_MAX = TPM2_PT_FIXED + 40,
• TPM2_PT_TOTAL_COMMANDS = TPM2_PT_FIXED + 41,
• TPM2_PT_LIBRARY_COMMANDS = TPM2_PT_FIXED + 42,
• TPM2_PT_VENDOR_COMMANDS = TPM2_PT_FIXED + 43,
• TPM2_PT_NV_BUFFER_MAX = TPM2_PT_FIXED + 44,
• TPM2_PT_MODES = TPM2_PT_FIXED + 45,
• TPM2_PT_MAX_CAP_BUFFER = TPM2_PT_FIXED + 46,
• TPM2_PT_VAR = TPM2_PT_GROUP * 2,
• TPM2_PT_PERMANENT = TPM2_PT_VAR + 0,
• TPM2_PT_STARTUP_CLEAR = TPM2_PT_VAR + 1,
• TPM2_PT_HR_NV_INDEX = TPM2_PT_VAR + 2,
• TPM2_PT_HR_LOADED = TPM2_PT_VAR + 3,
• TPM2_PT_HR_LOADED_AVAIL = TPM2_PT_VAR + 4,
• TPM2_PT_HR_ACTIVE = TPM2_PT_VAR + 5,
• TPM2_PT_HR_ACTIVE_AVAIL = TPM2_PT_VAR + 6,
• TPM2_PT_HR_TRANSIENT_AVAIL = TPM2_PT_VAR + 7,
• TPM2_PT_HR_PERSISTENT = TPM2_PT_VAR + 8,
• TPM2_PT_HR_PERSISTENT_AVAIL = TPM2_PT_VAR + 9,
• TPM2_PT_NV_COUNTERS = TPM2_PT_VAR + 10,
• TPM2_PT_NV_COUNTERS_AVAIL = TPM2_PT_VAR + 11,
• TPM2_PT_ALGORITHM_SET = TPM2_PT_VAR + 12,
• TPM2_PT_LOADED_CURVES = TPM2_PT_VAR + 13,
• TPM2_PT_LOCKOUT_COUNTER = TPM2_PT_VAR + 14,
• TPM2_PT_MAX_AUTH_FAIL = TPM2_PT_VAR + 15,
• TPM2_PT_LOCKOUT_INTERVAL = TPM2_PT_VAR + 16,
• TPM2_PT_LOCKOUT_RECOVERY = TPM2_PT_VAR + 17,
• TPM2_PT_NV_WRITE_RECOVERY = TPM2_PT_VAR + 18,
• TPM2_PT_AUDIT_COUNTER_0 = TPM2_PT_VAR + 19,
• TPM2_PT_AUDIT_COUNTER_1 = TPM2_PT_VAR + 20,

+}; /* 128 bytes is an arbitrary cap. This could be as large as TPM_BUFSIZE - 18

• bytes, but 128 is still a relatively large number of random bytes and

-- 2.25.1

BR, Jarkko