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

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

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.

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>
---
 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;
+
+	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,
+};
 
 /* 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
-- 
2.39.1