linux-kernel - Re: [PATCH v14 1/3] x86/tdx: Make __tdx_module

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Date:   Wed, 12 Oct 2022 10:13:50 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Kai Huang <kai.huang@...el.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v14 1/3] x86/tdx: Make __tdx_module_call() usable in
 driver module

Hi,

On 10/12/22 9:23 AM, Greg Kroah-Hartman wrote:
> On Wed, Oct 12, 2022 at 08:44:04AM -0700, Sathyanarayanan Kuppuswamy wrote:
>>
>>
>> On 10/12/22 7:27 AM, Borislav Petkov wrote:
>>> On Wed, Oct 12, 2022 at 06:35:56AM -0700, Sathyanarayanan Kuppuswamy wrote:
>>>> So we should create a new wrapper for this use case or use
>>>
>>> Yes, you got it - a new wrapper pls.
>>
>> Ok. I will add a new wrapper to get the TDREPORT. 
>>
>> +/*
>>
>> + * Add a wrapper for TDG.MR.REPORT TDCALL. It is used in TDX guest
>>
>> + * driver module to get the TDREPORT.
>>
>> + */
>>
>> +long tdx_mcall_get_report(void *reportdata, void *tdreport, u8 subtype)
> 
> Why "long"?

We used long because __tdx_module_call() call returns u64 value.

Alternatively, we can also check for return value of __tdx_module_call() here
and return 0/-EIO as return values. In this case we can change return value
to int.

> 
> Why void *?  Don't you have real types for these?

We use these buffers as an intermediary to transfer data between userspace and
the TDX module. In the kernel we don't consume these datas. So we did not define
the type of the data.

> 
> 
> 
>>
>> +{
>>
>> +       if (subtype || !reportdata || !tdreport)
>>
>> +               return -EINVAL;
> 
> How could that happen if you control all callers?

I have added it as a safety check against any incorrect usage in future. I
will remove it.


> 
> thanks,
> 
> greg k-h

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer