Re: [PATCH] tpm: Fix kexec crash due to access to ops NULL pointer (powerpc)

[Stefan Berger <stefanb@xxxxxxxxxxxxx>]

On 12/20/21 20:13, Jason Gunthorpe wrote:
> On Mon, Dec 20, 2021 at 08:05:58PM -0500, Stefan Berger wrote:
>
> > diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> > index ddaeceb7e109..4cb908349b31 100644
> > +++ b/drivers/char/tpm/tpm-chip.c
> > @@ -473,15 +473,8 @@ static void tpm_del_char_device(struct tpm_chip *chip)
> >          mutex_unlock(&idr_lock);
> >
> >          /* 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);
> > -               }
> > -       }
> > -       chip->ops = NULL;
> > -       up_write(&chip->ops_sem);
> > +       if (chip->ops)
> ops cannot be read without locking

This here could be an alternative:

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index ddaeceb7e109..7772b475ebc0 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -474,7 +474,7 @@ 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 (chip->ops && chip->flags & TPM_CHIP_FLAG_TPM2) {
                if (!tpm_chip_start(chip)) {
                        tpm2_shutdown(chip, TPM2_SU_CLEAR);
                        tpm_chip_stop(chip);

   Stefan


> Jason