linux-kernel - Re: [PATCH v2 10/10] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP

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Message-ID: <cc6e40872469ccfc58e7648f12bba5a0b1a54c65.camel@intel.com>
Date: Tue, 6 Aug 2024 12:18:29 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "Hansen, Dave" <dave.hansen@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "bp@...en8.de" <bp@...en8.de>, "peterz@...radead.org"
	<peterz@...radead.org>, "hpa@...or.com" <hpa@...or.com>, "mingo@...hat.com"
	<mingo@...hat.com>, "Williams, Dan J" <dan.j.williams@...el.com>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "tglx@...utronix.de"
	<tglx@...utronix.de>
CC: "Gao, Chao" <chao.gao@...el.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Edgecombe, Rick P"
	<rick.p.edgecombe@...el.com>, "x86@...nel.org" <x86@...nel.org>, "Yamahata,
 Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v2 10/10] x86/virt/tdx: Don't initialize module that
 doesn't support NO_RBP_MOD feature

On Mon, 2024-08-05 at 21:55 -0700, Williams, Dan J wrote:
> Kai Huang wrote:
> > Old TDX modules can clobber RBP in the TDH.VP.ENTER SEAMCALL.  However
> > RBP is used as frame pointer in the x86_64 calling convention, and
> > clobbering RBP could result in bad things like being unable to unwind
> > the stack if any non-maskable exceptions (NMI, #MC etc) happens in that
> > gap.
> > 
> > A new "NO_RBP_MOD" feature was introduced to more recent TDX modules to
> > not clobber RBP.  This feature is reported in the TDX_FEATURES0 global
> > metadata field via bit 18.
> > 
> > Don't initialize the TDX module if this feature is not supported [1].
> > 
> > Link: https://lore.kernel.org/all/c0067319-2653-4cbd-8fee-1ccf21b1e646@suse.com/T/#mef98469c51e2382ead2c537ea189752360bd2bef [1]
> > Signed-off-by: Kai Huang <kai.huang@...el.com>
> > Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>
> > ---
> > 
> > v1 -> v2:
> >  - Add tag from Nikolay.
> > 
> > ---
> >  arch/x86/virt/vmx/tdx/tdx.c | 17 +++++++++++++++++
> >  arch/x86/virt/vmx/tdx/tdx.h |  1 +
> >  2 files changed, 18 insertions(+)
> > 
> > diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> > index 3c19295f1f8f..ec6156728423 100644
> > --- a/arch/x86/virt/vmx/tdx/tdx.c
> > +++ b/arch/x86/virt/vmx/tdx/tdx.c
> > @@ -484,6 +484,18 @@ static int get_tdx_sysinfo(struct tdx_sysinfo *sysinfo)
> >  	return get_tdx_tdmr_sysinfo(&sysinfo->tdmr_info);
> >  }
> >  
> > +static int check_module_compatibility(struct tdx_sysinfo *sysinfo)
> 
> How about check_features()? Almost everything having to do with TDX
> concerns the TDX module, so using "module" in a symbol name rarely adds
> any useful context.

Yeah fine to me.  Will do.
> 
> > +{
> > +	u64 tdx_features0 = sysinfo->module_info.tdx_features0;
> > +
> > +	if (!(tdx_features0 & TDX_FEATURES0_NO_RBP_MOD)) {
> > +		pr_err("NO_RBP_MOD feature is not supported\n");
> 
> A user would have no idea with this error message how about something
> like:
> 
> pr_err("frame pointer (RBP) clobber bug present, upgrade TDX module\n");

Yeah this is certainly better.  Will do.  Thanks!