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

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Date: Mon, 20 May 2024 11:54:03 +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 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)?

View attachment "print_tdx_version.diff" of type "text/x-patch" (1584 bytes)