Re: [PATCH v2] tpm: disable hwrng for fTPM on some AMD designs

Guenter Roeck
2023-02-27T14:56:13Z

On Mon, Feb 20, 2023 at 12:07:28PM -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. As this is caused by faulty firmware, it
> is plausible that such a problem could also be reproduced by other TPM
> interactions, but this hasn't been shown by any user's testing or reports.
>
> It is hypothesized to be triggered more frequently by the use of the RNG
> because userspace software will fetch random numbers regularly.
>
> Intentionally continue to register other TPM functionality so that users
> that rely upon PCR measurements or any storage of data will still have
> access to it. If it's found later that another TPM functionality is
> exacerbating this problem a module parameter it can be turned off entirely
> and a module parameter can be introduced to allow users who rely upon
> fTPM functionality to turn it on even though this problem is present.
>
> 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>
> ---
> v1->v2:
> * Minor style from Jarkko's feedback
> * Move comment above function
> * Explain further in commit message
> ---
> drivers/char/tpm/tpm-chip.c | 61 ++++++++++++++++++++++++++++++-
> drivers/char/tpm/tpm.h | 73 +++++++++++++++++++++++++++++++++++++
> 2 files changed, 133 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index 741d8f3e8fb3..1b066d7a6e21 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -512,6 +512,64 @@ 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 +
> + */
> +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);
> + if (ret)
> + goto release;

This goto is unnecessary.

> +
> +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;

checkpatch:

CHECK: braces {} should be used on all arms of this statement
#200: FILE: drivers/char/tpm/tpm-chip.c:557:
+ if ((version >> 48) == 6) {
[...]
+ } else if ((version >> 48) == 3) {
[...]
+ } else
[...]

> +
> + 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 +579,8 @@ 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_amd_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
> --
> 2.34.1
>