| Message ID | 20230220180729.23862-1-mario.limonciello@amd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] tpm: disable hwrng for fTPM on some AMD designs | expand |
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> > --- > 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
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 >
On 2/27/23 08:55, Guenter Roeck wrote: > 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 > [...] It was requested by Jarko explicitly in v1 to do it this way. https://lore.kernel.org/lkml/Y+%2F6G+UlTI7GpW6o@kernel.org/ > >> + >> + 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 >>
On 2/27/23 06:58, Mario Limonciello wrote: [ ... ] >>> + 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 >> [...] > > It was requested by Jarko explicitly in v1 to do it this way. > > https://lore.kernel.org/lkml/Y+%2F6G+UlTI7GpW6o@kernel.org/ > Interesting. We live and learn. Guenter
[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
On Mon, Feb 27, 2023 at 08:58:37AM -0600, Mario Limonciello wrote: > On 2/27/23 08:55, Guenter Roeck wrote: > > 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 > > [...] > > It was requested by Jarko explicitly in v1 to do it this way. > > https://lore.kernel.org/lkml/Y+%2F6G+UlTI7GpW6o@kernel.org/ OK, you're right, it is my bad, I'm sorry about that. Send v3 with that feedback reverted. BR, Jarkko
On Tue, Feb 28, 2023 at 02:37:59AM +0000, Limonciello, Mario wrote: > [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 Thanks this tested-by can be in v3 because curly braces does not affect semantics. I can ack that then and pick it up. BR, Jarkko
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
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(-)