Re: [PATCH v7 03/20] x86/virt/tdx: Disable TDX if X2APIC is not enabled

[Huang, Kai]

On Sun, 2022-11-20 at 19:51 -0800, Sathyanarayanan Kuppuswamy wrote:
> 
> On 11/20/22 4:26 PM, Kai Huang wrote:
> > The MMIO/xAPIC interface has some problems, most notably the APIC LEAK
> 
> "some problems" looks more generic. May be we can be specific here. Like
> it has security issues?

It was quoted from below upstream commit id (I only kept the one that I quoted
to save space):

commit b8d1d163604bd1e600b062fb00de5dc42baa355f (tag: x86_apic_for_v6.1_rc1,
tip/x86/apic)
Author: Daniel Sneddon <daniel.sneddon@xxxxxxxxxxxxxxx>
Date:   Tue Aug 16 16:19:42 2022 -0700

    x86/apic: Don't disable x2APIC if locked
    
    ....
    
    The MMIO/xAPIC interface has some problems, most notably the APIC LEAK
    [1].  This bug allows an attacker to use the APIC MMIO interface to
    extract data from the SGX enclave.
    
    ....
    
    [1]: https://aepicleak.com/aepicleak.pdf
    
    Signed-off-by: Daniel Sneddon <daniel.sneddon@xxxxxxxxxxxxxxx>
    Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
    Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
    Tested-by: Neelima Krishnan <neelima.krishnan@xxxxxxxxx>
    Link:
https://lkml.kernel.org/r/20220816231943.1152579-1-daniel.sneddon@xxxxxxxxxxxxxxx


> 
> > [1].  This bug allows an attacker to use the APIC MMIO interface to
> > extract data from the SGX enclave.
> > 
> > TDX is not immune from this either.  Early check X2APIC and disable TDX
> > if X2APIC is not enabled, and make INTEL_TDX_HOST depend on X86_X2APIC.
> > 
> > [1]: https://aepicleak.com/aepicleak.pdf
> > 
> > Link: https://lore.kernel.org/lkml/d6ffb489-7024-ff74-bd2f-d1e06573bb82@xxxxxxxxx/
> > Link: https://lore.kernel.org/lkml/ba80b303-31bf-d44a-b05d-5c0f83038798@xxxxxxxxx/
> > Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> > ---
> > 
> > v6 -> v7:
> >  - Changed to use "Link" for the two lore links to get rid of checkpatch
> >    warning.
> > 
> > ---
> >  arch/x86/Kconfig            |  1 +
> >  arch/x86/virt/vmx/tdx/tdx.c | 11 +++++++++++
> >  2 files changed, 12 insertions(+)
> > 
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index cced4ef3bfb2..dd333b46fafb 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -1958,6 +1958,7 @@ config INTEL_TDX_HOST
> >  	depends on CPU_SUP_INTEL
> >  	depends on X86_64
> >  	depends on KVM_INTEL
> > +	depends on X86_X2APIC
> >  	help
> >  	  Intel Trust Domain Extensions (TDX) protects guest VMs from malicious
> >  	  host and certain physical attacks.  This option enables necessary TDX
> > diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> > index 982d9c453b6b..8d943bdc8335 100644
> > --- a/arch/x86/virt/vmx/tdx/tdx.c
> > +++ b/arch/x86/virt/vmx/tdx/tdx.c
> > @@ -12,6 +12,7 @@
> >  #include <linux/printk.h>
> >  #include <asm/msr-index.h>
> >  #include <asm/msr.h>
> > +#include <asm/apic.h>
> >  #include <asm/tdx.h>
> >  #include "tdx.h"
> >  
> > @@ -81,6 +82,16 @@ static int __init tdx_init(void)
> >  		goto no_tdx;
> >  	}
> >  
> > +	/*
> > +	 * TDX requires X2APIC being enabled to prevent potential data
> > +	 * leak via APIC MMIO registers.  Just disable TDX if not using
> > +	 * X2APIC.
> 
> Remove the double space.

Sorry which "double space"?

> 
> > +	 */
> > +	if (!x2apic_enabled()) {
> > +		pr_info("Disable TDX as X2APIC is not enabled.\n");
> 
> pr_warn()?

Why?