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

- From: Jason Gunthorpe \<jgg@ziepe.ca\>
- Date: 2021-12-21 01:13:25 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/12/1614939
- Thread: https://ratatoskr.run/linux-integrity/2021/12/1605081/t.md

```text
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

Jason
```