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 20:31:27 -0500
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
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 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