linux-kernel - Re: [PATCH v12 1/3] x86/tdx: Add TDX Guest attestation interface driver

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Date:   Thu, 8 Sep 2022 12:07:28 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.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 v12 1/3] x86/tdx: Add TDX Guest attestation interface
 driver

Hi,

On 9/7/22 10:31 PM, Greg Kroah-Hartman wrote:
> On Wed, Sep 07, 2022 at 05:27:20PM -0700, Kuppuswamy Sathyanarayanan wrote:
>> +	/*
>> +	 * Per TDX Module 1.0 specification, section titled
>> +	 * "TDG.MR.REPORT", REPORTDATA length is fixed as
>> +	 * TDX_REPORTDATA_LEN, TDREPORT length is fixed as
>> +	 * TDX_REPORT_LEN, and TDREPORT subtype is fixed as
>> +	 * 0. Also check for valid user pointers.
>> +	 */
>> +	if (!req.reportdata || !req.tdreport || req.subtype ||
>> +		req.rpd_len != TDX_REPORTDATA_LEN ||
>> +		req.tdr_len != TDX_REPORT_LEN)
>> +		return -EINVAL;
> 
> You never verify that your reserved[7] fields are actually set to 0,
> which means you can never use them in the future :(

Currently, we don't use those fields in our code. Why do we have to
make sure they are set to zero? Can't we add checks when we really use
them in future?

If your suggestion is to define allowed values of these fields for user,
we can add some help in structure definition of "tdx_report_req" in
arch/x86/include/uapi/asm/tdx.h

> 
> Please fix that up, thanks.
> 
> greg k-h

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer