Re: [PATCH] tpm: Disable RNG for all AMD fTPMs

On Wed Aug 2, 2023 at 12:18 AM EEST, Mario Limonciello wrote:

The TPM RNG functionality is not necessary for entropy when the CPU already supports the RDRAND instruction. The TPM RNG functionality was previously disabled on a subset of AMD fTPM series, but reports continue to show problems on some systems causing stutter root caused to TPM RNG functionality.

Expand disabling TPM RNG use for all AMD fTPMs whether they have versions that claim to have fixed or not. To accomplish this, move the detection into part of the TPM CRB registration and add a flag indicating that the TPM should opt-out of registration to hwrng.

Cc: stable@vger.kernel.org # 6.1.y+ Fixes: b006c439d58d ("hwrng: core - start hwrng kthread also for untrusted sources") Fixes: f1324bbc4011 ("tpm: disable hwrng for fTPM on some AMD designs") Reported-by: daniil.stas@posteo.net Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217719 Reported-by: bitlord0xff@gmail.com Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217212 Signed-off-by: Mario Limonciello mario.limonciello@amd.com

---

drivers/char/tpm/tpm-chip.c | 80 +++++++------------------------------ drivers/char/tpm/tpm_crb.c | 23 +++++++++++ include/linux/tpm.h | 7 ++++ 3 files changed, 44 insertions(+), 66 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c index cf5499e51999b..3154a5ef2611f 100644 --- a/drivers/char/tpm/tpm-chip.c +++ b/drivers/char/tpm/tpm-chip.c @@ -89,6 +89,14 @@ static void tpm_clk_disable(struct tpm_chip *chip) chip->ops->clk_enable(chip, false); } +static int tpm_check_flags(struct tpm_chip *chip) +{

• if (!chip->ops->check_flags)

• return 0;
  

• return chip->ops->check_flags(chip);

+}

Instead of adding a new callback, you should probably do the following in crb_acpi_add(), and get a much less complicated fix:

1. Call tpm_chip_bootstrap() (see tpm_tis_core_init()). 2. Set TPM_CHIP_FLAG_HWRNG_DISABLED if the conditions have been met. 3. Call tpm_chip_register().

/**

• tpm_chip_start() - power on the TPM
• @chip: a TPM chip to use

@@ -510,70 +518,6 @@ 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 +
• */

-#ifdef CONFIG_X86 -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);

-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;

-} -#else -static inline bool tpm_amd_is_rng_defective(struct tpm_chip *chip) -{

• return false;

-} -#endif /* CONFIG_X86 */

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); @@ -588,7 +532,7 @@ 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) ||

•    tpm_amd_is_rng_defective(chip))
  

•    tpm_is_rng_disabled(chip))
  

  return 0;

snprintf(chip->hwrng_name, sizeof(chip->hwrng_name), @@ -670,6 +614,10 @@ int tpm_chip_register(struct tpm_chip *chip) if (rc) return rc;

• rc = tpm_check_flags(chip);
• if (rc)

• return rc;
  

• tpm_sysfs_add_device(chip);

tpm_bios_log_setup(chip); @@ -719,7 +667,7 @@ void tpm_chip_unregister(struct tpm_chip *chip) { tpm_del_legacy_sysfs(chip); if (IS_ENABLED(CONFIG_HW_RANDOM_TPM) && !tpm_is_firmware_upgrade(chip) &&

•    !tpm_amd_is_rng_defective(chip))
  

•    !tpm_is_rng_disabled(chip))
  

  hwrng_unregister(&chip->hwrng); tpm_bios_log_teardown(chip); if (chip->flags & TPM_CHIP_FLAG_TPM2 && !tpm_is_firmware_upgrade(chip))

diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c index 1a5d09b185134..5614b68ef1905 100644 --- a/drivers/char/tpm/tpm_crb.c +++ b/drivers/char/tpm/tpm_crb.c @@ -463,6 +463,28 @@ static bool crb_req_canceled(struct tpm_chip *chip, u8 status) return (cancel & CRB_CANCEL_INVOKE) == CRB_CANCEL_INVOKE; } +static int crb_check_flags(struct tpm_chip *chip) +{

• u32 val;
• int ret;
• ret = crb_request_locality(chip, 0);
• if (ret)

• return ret;
  

• ret = tpm2_get_tpm_pt(chip, TPM2_PT_MANUFACTURER, &val, NULL);
• if (ret)

• goto release;
  

• if (val == 0x414D4400U /* AMD */)

• chip->flags |= TPM_CHIP_FLAG_HWRNG_DISABLED;
  

+release:

• crb_relinquish_locality(chip, 0);
• return ret;

+}

static const struct tpm_class_ops tpm_crb = { .flags = TPM_OPS_AUTO_STARTUP, .status = crb_status, @@ -476,6 +498,7 @@ static const struct tpm_class_ops tpm_crb = { .relinquish_locality = crb_relinquish_locality, .req_complete_mask = CRB_DRV_STS_COMPLETE, .req_complete_val = CRB_DRV_STS_COMPLETE,

• .check_flags = crb_check_flags,

}; static int crb_check_resource(struct acpi_resource *ares, void *data) diff --git a/include/linux/tpm.h b/include/linux/tpm.h index 6a1e8f1572551..aeb84944b0ca4 100644 --- a/include/linux/tpm.h +++ b/include/linux/tpm.h @@ -82,6 +82,7 @@ struct tpm_class_ops { int (*request_locality)(struct tpm_chip *chip, int loc); int (*relinquish_locality)(struct tpm_chip *chip, int loc); void (*clk_enable)(struct tpm_chip *chip, bool value);

• int (*check_flags)(struct tpm_chip *chip);

}; #define TPM_NUM_EVENT_LOG_FILES 3 @@ -283,6 +284,7 @@ enum tpm_chip_flags { TPM_CHIP_FLAG_FIRMWARE_POWER_MANAGED = BIT(6), TPM_CHIP_FLAG_FIRMWARE_UPGRADE = BIT(7), TPM_CHIP_FLAG_SUSPENDED = BIT(8),

• TPM_CHIP_FLAG_HWRNG_DISABLED = BIT(9),

}; #define to_tpm_chip(d) container_of(d, struct tpm_chip, dev) @@ -417,6 +419,11 @@ static inline u32 tpm2_rc_value(u32 rc) return (rc & BIT(7)) ? rc & 0xff : rc; } +static inline bool tpm_is_rng_disabled(struct tpm_chip *chip) +{

• return chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED;

+}

Please open code to the call sites.

Wrapping a flag check is not very useful and makes the bug fix only more complex.

#if defined(CONFIG_TCG_TPM) || defined(CONFIG_TCG_TPM_MODULE) extern int tpm_is_tpm2(struct tpm_chip *chip); -- 2.34.1

BR, Jarkko