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") Fixes: 39d0099f9439 ("powerpc/pseries: Add shutdown() to vio_driver and vio_bus") Cc: stable@vger.kernel.org Tested-by: Stefan Berger stefanb@linux.ibm.com Reviewed-by: Stefan Berger stefanb@linux.ibm.com Signed-off-by: Lino Sanfilippo LinoSanfilippo@gmx.de --- Changes in v3: - added tags for Stefans review and test - corrected the source code comment
Changes in 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..03122d624670 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); + /* In case that the SPI master is unregistered in its drivers + * shutdown handler, tpm_class_shutdown() has already been called + * and set chip->ops to NULL. So check if it is still valid. + */ + 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: bc491fb12513e79702c6f936c838f792b5389129