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Subject: Re: [PATCH v2][next] scsi: mpt3sas: Replace one-element array with
 flexible-array in struct _MPI2_CONFIG_PAGE_IO_UNIT_3
To:     Kees Cook <keescook@chromium.org>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc:     James Bottomley <jejb@linux.ibm.com>,
        Sathya Prakash <sathya.prakash@broadcom.com>,
        Sreekanth Reddy <sreekanth.reddy@broadcom.com>,
        Suganath Prabu Subramani 
        <suganath-prabu.subramani@broadcom.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        MPT-FusionLinux.pdl@broadcom.com, linux-scsi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
References: <20210202235118.GA314410@embeddedor>
 <20210308193237.GA212624@embeddedor>
 <88d9dda39a70df25b48e72247b9752d3dc5e2e8d.camel@linux.ibm.com>
 <20210308204129.GA214076@embeddedor> <202103101058.16ED27BE3@keescook>
From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Message-ID: <855e73f8-9b84-25b9-01e3-8ce368165b25@embeddedor.com>
Date:   Wed, 10 Mar 2021 18:06:52 -0600
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On 3/10/21 13:07, Kees Cook wrote:

>> diff --git a/drivers/scsi/mpt3sas/mpi/mpi2_cnfg.h b/drivers/scsi/mpt3sas/mpi/mpi2_cnfg.h
>> index 43a3bf8ff428..d00431f553e1 100644
>> --- a/drivers/scsi/mpt3sas/mpi/mpi2_cnfg.h
>> +++ b/drivers/scsi/mpt3sas/mpi/mpi2_cnfg.h
>> @@ -992,7 +992,7 @@ typedef struct _MPI2_CONFIG_PAGE_IO_UNIT_1 {
>>   *one and check the value returned for GPIOCount at runtime.
>>   */
>>  #ifndef MPI2_IO_UNIT_PAGE_3_GPIO_VAL_MAX
>> -#define MPI2_IO_UNIT_PAGE_3_GPIO_VAL_MAX    (1)
>> +#define MPI2_IO_UNIT_PAGE_3_GPIO_VAL_MAX    (36)
>>  #endif
>>
>>  typedef struct _MPI2_CONFIG_PAGE_IO_UNIT_3 {
>> diff --git a/drivers/scsi/mpt3sas/mpt3sas_ctl.c b/drivers/scsi/mpt3sas/mpt3sas_ctl.c
>> index 44f9a05db94e..23fcf29bfd67 100644
>> --- a/drivers/scsi/mpt3sas/mpt3sas_ctl.c
>> +++ b/drivers/scsi/mpt3sas/mpt3sas_ctl.c
>> @@ -3203,7 +3203,7 @@ BRM_status_show(struct device *cdev, struct device_attribute *attr,
>>  {
>>         struct Scsi_Host *shost = class_to_shost(cdev);
>>         struct MPT3SAS_ADAPTER *ioc = shost_priv(shost);
>> -       Mpi2IOUnitPage3_t *io_unit_pg3 = NULL;
>> +       Mpi2IOUnitPage3_t io_unit_pg3;
>>         Mpi2ConfigReply_t mpi_reply;
>>         u16 backup_rail_monitor_status = 0;
>>         u16 ioc_status;
>> @@ -3221,16 +3221,10 @@ BRM_status_show(struct device *cdev, struct device_attribute *attr,
>>                 goto out;
>>
>>         /* allocate upto GPIOVal 36 entries */
>> -       sz = offsetof(Mpi2IOUnitPage3_t, GPIOVal) + (sizeof(u16) * 36);
>> -       io_unit_pg3 = kzalloc(sz, GFP_KERNEL);
>> -       if (!io_unit_pg3) {
>> -               rc = -ENOMEM;
>> -               ioc_err(ioc, "%s: failed allocating memory for iounit_pg3: (%d) bytes\n",
>> -                       __func__, sz);
>> -               goto out;
>> -       }
>> +       sz = sizeof(io_unit_pg3);
>> +       memset(&io_unit_pg3, 0, sz);
> 
> I like this a lot. It makes the code way simpler.
> 
> Putting this on the stack makes it faster, and it's less than 100 bytes,
> which seems entirely reasonable.
> 
>>
>> -       if (mpt3sas_config_get_iounit_pg3(ioc, &mpi_reply, io_unit_pg3, sz) !=
>> +       if (mpt3sas_config_get_iounit_pg3(ioc, &mpi_reply, &io_unit_pg3, sz) !=
> 
> The only thing I can imagine is if this ends up doing DMA, which isn't
> allowed on the stack. However, in looking down through the call path,
> it's _copied_ into DMA memory, so this appears entirely safe.
>  
> Can you send this as a "normal" patch? Feel free to include:
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>

Done: https://lore.kernel.org/lkml/20210310235951.GA108661@embeddedor/

Thanks for the comments!
--
Gustavo