[PATCH] tpm_tis: Add a check for invalid status

* [PATCH] tpm_tis: Add a check for invalid status
@ 2020-09-28 18:00 James Bottomley
  2020-09-28 18:33 ` Jason Gunthorpe
  0 siblings, 1 reply; 5+ messages in thread
From: James Bottomley @ 2020-09-28 18:00 UTC (permalink / raw)
  To: linux-integrity; +Cc: Jarkko Sakkinen, Peter Huewe, Jason Gunthorpe

Some TIS based TPMs can return 0xff to status reads if the locality
hasn't been properly requested.  Detect this condition by checking the
bits that the TIS spec specifies must return zero are clear and return
zero in that case.  Also drop a warning so the problem can be
identified in the calling path and fixed (usually a missing
try_get_ops()).

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---

This is the patch I've been using to catch and kill all the points in
the stack where we're not properly using get/put ops on the tpm chip.

 drivers/char/tpm/tpm_tis_core.c | 11 +++++++++++
 drivers/char/tpm/tpm_tis_core.h |  1 +
 2 files changed, 12 insertions(+)

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 65ab1b027949..92c51c6cfd1b 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -239,6 +239,17 @@ static u8 tpm_tis_status(struct tpm_chip *chip)
 	if (rc < 0)
 		return 0;
 
+	if (unlikely((status & TPM_STS_READ_ZERO) != 0)) {
+		/*
+		 * If this trips, the chances are the read is
+		 * returning 0xff because the locality hasn't been
+		 * acquired.  Usually because tpm_try_get_ops() hasn't
+		 * been called before doing a TPM operation.
+		 */
+		WARN_ONCE(1, "TPM returned invalid status\n");
+		return 0;
+	}
+
 	return status;
 }
 
diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
index 7337819f5d7b..9b2d32a59f67 100644
--- a/drivers/char/tpm/tpm_tis_core.h
+++ b/drivers/char/tpm/tpm_tis_core.h
@@ -34,6 +34,7 @@ enum tis_status {
 	TPM_STS_GO = 0x20,
 	TPM_STS_DATA_AVAIL = 0x10,
 	TPM_STS_DATA_EXPECT = 0x08,
+	TPM_STS_READ_ZERO = 0x23, /* bits that must be zero on read */
 };
 
 enum tis_int_flags {
-- 
2.26.2



^ permalink raw reply related	[flat|nested] 5+ messages in thread