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

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Date: Fri, 17 May 2024 17:41:08 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Juergen Gross <jgross@...e.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, 
	linux-coco@...ts.linux.dev, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/kvm/tdx: Save %rbp in TDX_MODULE_CALL

On Fri, May 17, 2024 at 05:39:51PM +0300, Kirill A. Shutemov wrote:
> On Fri, May 17, 2024 at 04:08:03PM +0200, Juergen Gross wrote:
> > On 17.05.24 15:55, Kirill A. Shutemov wrote:
> > > On Fri, May 17, 2024 at 02:14:50PM +0200, Juergen Gross wrote:
> > > > While testing TDX host support patches, a crash of the host has been
> > > > observed a few instructions after doing a seamcall. Reason was a
> > > > clobbered %rbp (set to 0), which occurred in spite of the TDX module
> > > > offering the feature NOT to modify %rbp across TDX module calls.
> > > > 
> > > > In order not having to build the host kernel with CONFIG_FRAME_POINTER,
> > > > save %rbp across a seamcall/tdcall.
> > > 
> > > There's a feature in TDX module 1.5 that prevents RBP modification across
> > > TDH.VP.ENTER SEAMCALL. See NO_RBP_MOD in TDX Module 1.5 ABI spec.
> > > 
> > > I think it has to be enabled for all TDs and TDX modules that don't
> > > support it need to be rejected.
> > > 
> > 
> > Yes, I know. I'm using the patch series:
> > 
> >   [PATCH v19 000/130] KVM TDX basic feature support
> > 
> > which I think does exactly that (see setup_tdparams() and tdx_module_setup()).
> 
> Looks like the check is broken:
> 
> https://lore.kernel.org/all/46mh5hinsv5mup2x7jv4iu2floxmajo2igrxb3haru3cgjukbg@v44nspjozm4h/

Err.. I think I confused myself. Please ignore.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov