linux-kernel - Re: [PATCH v13 003/113] KVM: TDX: Initialize the TDX module when loading the KVM intel kernel module

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <f02637a56848cff1a39a2c7e2350c11b180a87ea.camel@intel.com>
Date:   Wed, 29 Mar 2023 23:17:31 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>
CC:     "Christopherson,, Sean" <seanjc@...gle.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "zhi.wang.linux@...il.com" <zhi.wang.linux@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v13 003/113] KVM: TDX: Initialize the TDX module when
 loading the KVM intel kernel module

On Wed, 2023-03-29 at 14:56 -0700, Isaku Yamahata wrote:
> On Wed, Mar 29, 2023 at 01:13:45AM +0000,
> "Huang, Kai" <kai.huang@...el.com> wrote:
> 
> > > 
> > > > >  
> > > > > +	/*
> > > > > +	 * TDX requires those methods to enable VMXON by
> > > > > +	 * kvm_hardware_enable/disable_all()
> > > > > +	 */
> > > > > +	static_call_update(kvm_x86_check_processor_compatibility,
> > > > > +			   ops->runtime_ops->check_processor_compatibility);
> > > > > +	static_call_update(kvm_x86_hardware_enable,
> > > > > +			   ops->runtime_ops->hardware_enable);
> > > > > +	static_call_update(kvm_x86_hardware_disable,
> > > > > +			   ops->runtime_ops->hardware_disable);
> > > > >  	r = ops->hardware_setup();
> > > > >  	if (r != 0)
> > > > >  		goto out_mmu_exit;
> > > > 
> > > > Hmm.. I think this is ugly.  Perhaps we should never do any
> > > > static_call(kvm_x86_xxx)() in hardware_setup(), because hardware_setup() is
> > > > called before kvm_ops_update() and may update vendor's kvm_x86_ops.
> > > > 
> > > > So probably use hardware_enable_all() in hardware_setup() is a bad idea.
> > > > 
> > > > I think we have below options on how to handle:
> > > > 
> > > > 1) Use VMX's kvm_x86_ops directly in tdx_hardware_setup().  For instance,
> > > > something like below:
> > > > 
> > > > int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
> > > > {
> > > > 	...
> > > > 
> > > > 	cpus_read_lock();
> > > > 	r = on_each_cpu(vt_x86_ops.hardware_enable, ...);
> > > > 	if (!r)
> > > > 		r = tdx_module_setup();
> > > > 	on_each_cpu(vt_x86_ops.hardware_disable, ...);
> > > > 	cpus_read_unlock();
> > > > 
> > > > 	...
> > > > }
> > > > 
> > > > But this doesn't clean up nicely when there's some particular cpus fail to do
> > > > hardware_enable().  To clean up nicely, we do need additional things similar to
> > > > the hardware_enable_all() code path: a per-cpu variable or a cpumask_t + a
> > > > wrapper of vt_x86_ops->hardware_enable() to track which cpus have done
> > > > hardware_enable() successfully.
> > > > 
> > > > 2) Move those static_call_update() into tdx_hardware_setup() so they are TDX
> > > > code self-contained.  But this would require exposing kvm_x86_ops as symbol,
> > > > which isn't nice either.
> > > > 
> > > > 3) Introduce another kvm_x86_init_ops->hardware_post_setup(), which is called
> > > > after kvm_ops_update().
> > > > 
> > > > Personally, I think 3) perhaps is the most elegant one, but not sure whether
> > > > Sean/Paolo has any opinion.
> > > 
> > > I think we can simply update the ops before calling hardware_enable() and
> > > clean up ops on failure.
> > > 
> > > 
> > 
> > This doesn't work because hardware_setup() may update vendor's kvm_x86_ops.
> > 
> > If you do kvm_ops_update() before hardware_setup(), you need to manually update
> > those updated (in hardware_setup()) callbacks again after. 
> 
> We can call kvm_ops_update() twice before and after hardware_setup().
> 

Personally I think it's too ugly.