Some SPI controller drivers unregister the controller in the shutdown
handler (e.g. BCM2835). If such a controller is used with a TPM 2 slave
chip->ops may be accessed when it is already NULL:
At system shutdown the pre-shutdown handler tpm_class_shutdown() shuts down
TPM 2 and sets chip->ops to NULL. Then at SPI controller unregistration
tpm_tis_spi_remove() is called and eventually calls tpm_del_char_device()
which tries to shut down TPM 2 again. Thereby it accesses chip->ops again:
(tpm_del_char_device calls tpm_chip_start which calls tpm_clk_enable which
calls chip->ops->clk_enable).
Avoid the NULL pointer access by testing if chip->ops is valid and skipping
the TPM 2 shutdown procedure in case it is NULL.
Fixes: dcbeab1946454 ("tpm: fix crash in tpm_tis deinitialization")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Lino Sanfilippo <LinoSanfilippo@xxxxxx>
---
Changes to v2:
- rephrased the commit message to clarify the circumstances under which
this bug triggers (as requested by Jarkko)
I was able to reproduce this issue with a SLB 9670 TPM chip controlled by
a BCM2835 SPI controller.
The approach to fix this issue in the BCM2835 driver was rejected after a
discussion on the mailing list:
https://marc.info/?l=linux-integrity&m=163285906725367&w=2
The reason for the rejection was the realization, that this issue should rather
be fixed in the TPM code:
https://marc.info/?l=linux-spi&m=163311087423271&w=2
So this is the reworked version of a patch that is supposed to do that.
drivers/char/tpm/tpm-chip.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index ddaeceb7e109..7960da490e72 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -474,13 +474,19 @@ static void tpm_del_char_device(struct tpm_chip *chip)
/* Make the driver uncallable. */
down_write(&chip->ops_sem);
- if (chip->flags & TPM_CHIP_FLAG_TPM2) {
- if (!tpm_chip_start(chip)) {
- tpm2_shutdown(chip, TPM2_SU_CLEAR);
- tpm_chip_stop(chip);
+ /* Check if chip->ops is still valid: In case that the controller
+ * drivers shutdown handler unregisters the controller in its
+ * shutdown handler we are called twice and chip->ops to NULL.
+ */
+ if (chip->ops) {
+ if (chip->flags & TPM_CHIP_FLAG_TPM2) {
+ if (!tpm_chip_start(chip)) {
+ tpm2_shutdown(chip, TPM2_SU_CLEAR);
+ tpm_chip_stop(chip);
+ }
}
+ chip->ops = NULL;
}
- chip->ops = NULL;
up_write(&chip->ops_sem);
}
base-commit: a7904a538933c525096ca2ccde1e60d0ee62c08e
--
2.34.1
