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

Limonciello, Mario
2023-02-28T02:38:13Z

[Public]

> -----Original Message-----
> From: Limonciello, Mario
> Sent: Monday, February 27, 2023 08:53
> To: Peter Huewe <peterhuewe@gmx.de>; Jarkko Sakkinen
> <jarkko@kernel.org>; Jason Gunthorpe <jgg@ziepe.ca>; Dominik Brodowski
> <linux@dominikbrodowski.net>; Herbert Xu
> <herbert@gondor.apana.org.au>
> Cc: stable@vger.kernel.org; Thorsten Leemhuis
> <regressions@leemhuis.info>; James Bottomley
> <James.Bottomley@hansenpartnership.com>; Jason A . Donenfeld
> <Jason@zx2c4.com>; linux-integrity@vger.kernel.org; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH v2] tpm: disable hwrng for fTPM on some AMD designs
>
> On 2/20/23 12:07, 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
>
> One of the reporters on the kernel bugzilla did confirm the v2 patch,
> forwarding their tag.
>
> Tested-by: Bell <1138267643@qq.com>

Here's another tag.

Tested-by: reach622@mailcuk.com

> > ---
> > 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;
> > +
> > +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;
> > +}
> > +
> > 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