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

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Message-ID: <a9bbb31e6660343e95d3351febc6e3b9661a7944.camel@intel.com>
Date: Thu, 23 May 2024 12:26:43 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"jgross@...e.com" <jgross@...e.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 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.


View attachment "check_no_rbp_mod.diff" of type "text/x-patch" (2708 bytes)