Re: [PATCH RFC] tpm: disable hwrng for known-defective AMD RNGs

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Feb 09, 2023 at 12:31:20PM -0300, Jason A. Donenfeld wrote:
> Do not register a hwrng for certain AMD TPMs that are running an old

What do you mean by "certain AMD TPMs"?

> known-buggy revision. Do this by probing the TPM2_PT_MANUFACTURER,

Which revision?

> TPM2_PT_FIRMWARE_VERSION_1, and TPM2_PT_FIRMWARE_VERSION_2 properties,
> and failing when an "AMD"-manufactured TPM2 chip is below a threshold.

What do you mean by "threshold"?

This also lacks desription of:

1. What kind of changes are done.
2. Why do they they are reasonable.

E.g. "failing" does not have any useful and measurable meaning...

> BROKEN BROKEN BROKEN - I just made the version numbers up and haven't
> tested this because I don't actually have hardware for it. I'm posting
> this so that Mario can take over its development and submit a v2 himself
> once he has confirmed the versioning info from inside AMD.

Is this paragraph meant for commit log?

> Suggested-by: Mario Limonciello <mario.limonciello@amd.com>
> Cc: Jarkko Sakkinen <jarkko@kernel.org>
> Cc: Thorsten Leemhuis <regressions@leemhuis.info>
> Cc: James Bottomley <James.Bottomley@hansenpartnership.com>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  drivers/char/tpm/tpm-chip.c | 34 ++++++++++++++++-
>  drivers/char/tpm/tpm.h      | 73 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 106 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index 741d8f3e8fb3..e0f8134d31a3 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -512,6 +512,37 @@ static int tpm_add_legacy_sysfs(struct tpm_chip *chip)
>  	return 0;
>  }
>  
> +static bool tpm_is_rng_defective(struct tpm_chip *chip)
> +{
> +	int ret;
> +	u32 val1, val2;
> +	u64 version;
> +
> +	/* No known-broken TPM1 chips. */
> +	if (!(chip->flags & TPM_CHIP_FLAG_TPM2))
> +		return false;
> +
> +	/* Only known-broken are AMD. */
> +	ret = tpm2_get_tpm_pt(chip, TPM2_PT_MANUFACTURER, &val1, NULL);
> +	if (ret < 0 || val1 != 0x414D4400U /* AMD */)
> +		return false;
> +
> +	/* Grab and concat the version values. */
> +	ret = tpm2_get_tpm_pt(chip, TPM2_PT_FIRMWARE_VERSION_1, &val1, NULL);
> +	if (ret < 0)
> +		return false;
> +	ret = tpm2_get_tpm_pt(chip, TPM2_PT_FIRMWARE_VERSION_2, &val2, NULL);
> +	if (ret < 0)
> +		return false;
> +	version = ((u64)val1 << 32) | val2;
> +
> +	/* Versions below 3.4e.2.9 are broken. */
> +	if (version < 0x0003004E0002009ULL)
> +		return true;
> +
> +	return false;
> +}
> +
>  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 +552,8 @@ 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 24ee4e1cc452..830014a26609 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
> -- 
> 2.39.1
> 

BR, Jarkko