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

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Date:   Mon, 20 Dec 2021 21:13:20 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Stefan Berger <stefanb@...ux.ibm.com>
Cc:     Tyrel Datwyler <tyreld@...ux.ibm.com>, jarkko@...nel.org,
        peterhuewe@....de, linux-integrity@...r.kernel.org,
        Korrapati.Likhitha@....com, pavrampu@...ibm.com,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, gcwilson@...ibm.com,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] tpm: Fix kexec crash due to access to ops NULL pointer
 (powerpc)

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