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

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Date: Thu, 23 May 2024 14:43:02 +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 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


Juergen