linux-kernel - Re: [PATCH] x86/kvm/tdx: Save %rbp in TDX_MODULE

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Date: Fri, 24 May 2024 07:46:55 +0200
From: Jürgen Groß <jgross@...e.com>
To: "Huang, Kai" <kai.huang@...el.com>,
 "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
 "Hansen, Dave" <dave.hansen@...el.com>
Cc: "bp@...en8.de" <bp@...en8.de>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
 "hpa@...or.com" <hpa@...or.com>, "mingo@...hat.com" <mingo@...hat.com>,
 "tglx@...utronix.de" <tglx@...utronix.de>, "x86@...nel.org"
 <x86@...nel.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>,
 "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>
Subject: Re: [PATCH] x86/kvm/tdx: Save %rbp in TDX_MODULE_CALL

On 24.05.24 00:34, Huang, Kai wrote:
> 
> 
> On 24/05/2024 12:43 am, Jürgen Groß wrote:
>> On 23.05.24 14:26, Huang, Kai wrote:
>>> On Thu, 2024-05-23 at 10:30 +0000, Huang, Kai wrote:
>>>> On Thu, 2024-05-23 at 07:56 +0200, Jürgen Groß wrote:
>>>>> On 20.05.24 13:54, Huang, Kai wrote:
>>>>>> On Fri, 2024-05-17 at 09:48 -0700, Dave Hansen wrote:
>>>>>>> On 5/17/24 08:58, Juergen Gross wrote:
>>>>>>>> On 17.05.24 17:52, Dave Hansen wrote:
>>>>>>> ..
>>>>>>>>> Once we have the specific TDX module version, we can go ask the folks
>>>>>>>>> who write it if there were any RBP clobbering bugs.
>>>>>>>>
>>>>>>>> Okay, how to get the TDX module version?
>>>>>>>
>>>>>>> You need something like this:
>>>>>>>
>>>>>>>> https://lore.kernel.org/all/20231012134136.1310650-1-yi.sun@intel.com/
>>>>>>
>>>>>> This one prints TDX version info in the TDX guest, but not host.
>>>>>>
>>>>>> The attached diff prints the TDX version (something like below) during
>>>>>> module initialization, and should meet Juergen's needs for temporary use:
>>>>>>
>>>>>> [  113.543538] virt/tdx: module verson: major 1, minor 5, internal 0
>>>>>>
>>>>>>>
>>>>>>> .. and yeah, this needs to be upstream.
>>>>>>>
>>>>>>
>>>>>>   From this thread I think it makes sense to add code to the TDX host code
>>>>>> to print the TDX version during module initialization.  I'll start to work
>>>>>> on this.
>>>>>>
>>>>>> One thing is from the spec TDX has "4 versions": major, minor, update,
>>>>>> internal.  They are all 16-bit, and the overall version can be written in:
>>>>>>
>>>>>>     <Major>.<Minor>.<Update>.<Internal>, e.g., 1.5.05.01
>>>>>>
>>>>>> (see TDX module 1.5 API spec, section 3.3.2 "TDX Module Version".)
>>>>>>
>>>>>> The attached diff only prints major, minor and internal, but leaves the
>>>>>> update out because I believe it is for module runtime update (yet to
>>>>>> confirm).
>>>>>>
>>>>>> Given there are 4 versions, I think it makes sense to implement reading
>>>>>> them based on this patchset ...
>>>>>>
>>>>>> https://lore.kernel.org/kvm/6940c326-bfca-4c67-badf-ab5c086bf492@intel.com/T/
>>>>>>
>>>>>> ... which extends the global metadata reading code to support any
>>>>>> arbitrary struct and all element sizes (although all 4 versions are 16-
>>>>>> bit)?
>>>>>
>>>>> With that I got:
>>>>>
>>>>> [   29.328484] virt/tdx: module verson: major 1, minor 5, internal 0
>>>>>
>>>>>
>>>>
>>>> Let me check TDX module guys on this and get back to you.
>>>
>>> Hi Jurgen,
>>>
>>> I was told the module starting with "1.5.06." has NO_RBP_MOD support.
>>>
>>> And I think I was wrong about the <update> part of the version, and we
>>> need that to determine the third part of the module version.
>>>
>>> I was also told the 1.5.06 module hasn't been released to public yet, so I
>>> guess your module doesn't support it.
>>>
>>> I did another patch (attached) to check NO_RBP_MOD and reject module
>>> initialization if it is not supported, and print out module version:
>>>
>>> [  146.566641] virt/tdx: NO_RBP_MOD feature is not supported
>>> [  146.572797] virt/tdx: module verson: 1.5.0.0
>>> [  146.577731] virt/tdx: module initialization failed (-22)
>>>
>>> You can have another try to verify at your side, if that helps.
>>>
>>
>> [   29.362806] virt/tdx: 4071192 KB allocated for PAMT
>> [   29.362828] virt/tdx: module verson: 1.5.1.0
>> [   29.362830] virt/tdx: module initialized
> 
> Seems your module supports NO_RBP_MOD.
> 
> This feature is per-VM and also requires to be explicitly opt-in when creating 
> the guest.  Could you check in your code whether the setup_tdparams() function 
> has below code?
> 
>      td_params->exec_controls = TDX_CONTROL_FLAG_NO_RBP_MOD;

I can confirm that it does have that.


Juergen