Date:   Mon, 20 Dec 2021 21:13:20 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Stefan Berger <stefanb@linux.ibm.com>
Cc:     Tyrel Datwyler <tyreld@linux.ibm.com>, jarkko@kernel.org,
        peterhuewe@gmx.de, linux-integrity@vger.kernel.org,
        Korrapati.Likhitha@ibm.com, pavrampu@in.ibm.com,
        linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org, gcwilson@us.ibm.com,
        linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] tpm: Fix kexec crash due to access to ops NULL pointer
 (powerpc)
Message-ID: <20211221011320.GM6467@ziepe.ca>
References: <20211212012804.1555661-1-stefanb@linux.ibm.com>
 <1052cd36-1b85-5d36-045f-5c5bf9f0fc4e@linux.ibm.com>
 <d9eafa8f-4006-4bc2-c09b-6b02a14c6ef3@linux.ibm.com>
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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