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

["Jason A. Donenfeld" <Jason@zx2c4.com>]

On Thu, Feb 9, 2023 at 12:41 PM Limonciello, Mario
<mario.limonciello@amd.com> wrote:
>
> On 2/9/2023 09:31, Jason A. Donenfeld wrote:
> > Do not register a hwrng for certain AMD TPMs that are running an old
> > known-buggy revision. Do this by probing the TPM2_PT_MANUFACTURER,
> > TPM2_PT_FIRMWARE_VERSION_1, and TPM2_PT_FIRMWARE_VERSION_2 properties,
> > and failing when an "AMD"-manufactured TPM2 chip is below a threshold.
> >
> > 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.
>
> Thanks, happy to do that.  As I'll take over some comments are inline
> mostly for my future self when this is resubmitted.
>
> Perhaps one of the people who can reproduce this right now can confirm
> this works?  The version number string should at least trigger one of
> the reported systems to avoid doing this.
>
> >
> > 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>
>
> At least as a note for myself this needs:
> 1. 'Link' tag to the public advisory for this fTPM issue
> 2. A 'Fixes' tag to the commit that enabled fTPM as a hwrng source by
> default and exposed the issue.
> 3. A 'Link' tag to the bugzilla.
>
> > ---
> >   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;
>
> We probably want to also do a 'dev_info_once' or 'dev_warn_once' here to
> let people know that they're not getting a fTPM RNG so it's not a surprise.

AFAICT, this runs once per TPM device. So maybe a simple dev_warn()
without the _once part will be good, so you actually see in dmesg each
buggy device.

>
> > +
> > +     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,
> > +};
> >
>
> I guess these properties should be split out to a separate patch in a
> series.

That will make backporting this more annoying. Up to Jarkko,
obviously, but personally I wouldn't bother.