Re: [Qemu-devel] [edk2-rfc] [edk2-devel] CPU hotplug using SMM with QEMU+OVMF

[Yao, Jiewen]

Thank you Mike!

That is good reference on the real hardware behavior. (Glad it is public.)

For threat model, the unique part in virtual environment is temp RAM.
The temp RAM in real platform is per CPU cache, while the temp RAM in virtual 
platform is global memory.
That brings one more potential attack surface in virtual environment, if 
hot-added CPU need run code with stack or heap before SMI rebase.

Other threats, such as SMRAM or DMA, are same.

Thank you
Yao Jiewen


> -----Original Message-----
> From: Kinney, Michael D
> Sent: Friday, August 23, 2019 9:03 AM
> To: Paolo Bonzini <address@hidden>; Laszlo Ersek
> <address@hidden>; address@hidden; Yao, Jiewen
> <address@hidden>; Kinney, Michael D <address@hidden>
> Cc: Alex Williamson <address@hidden>; address@hidden;
> qemu devel list <address@hidden>; Igor Mammedov
> <address@hidden>; Chen, Yingwen <address@hidden>;
> Nakajima, Jun <address@hidden>; Boris Ostrovsky
> <address@hidden>; Joao Marcal Lemos Martins
> <address@hidden>; Phillip Goerl <address@hidden>
> Subject: RE: [edk2-rfc] [edk2-devel] CPU hotplug using SMM with
> QEMU+OVMF
> 
> Paolo,
> 
> I find the following links related to the discussions here
> along with one example feature called GENPROTRANGE.
> 
> https://csrc.nist.gov/CSRC/media/Presentations/The-Whole-is-Greater/ima
> ges-media/day1_trusted-computing_200-250.pdf
> https://cansecwest.com/slides/2017/CSW2017_Cuauhtemoc-Rene_CPU_Ho
> t-Add_flow.pdf
> https://www.mouser.com/ds/2/612/5520-5500-chipset-ioh-datasheet-1131
> 292.pdf
> 
> Best regards,
> 
> Mike
> 
> > -----Original Message-----
> > From: Paolo Bonzini [mailto:address@hidden]
> > Sent: Thursday, August 22, 2019 4:12 PM
> > To: Kinney, Michael D <address@hidden>;
> > Laszlo Ersek <address@hidden>; address@hidden;
> > Yao, Jiewen <address@hidden>
> > Cc: Alex Williamson <address@hidden>;
> > address@hidden; qemu devel list <qemu-
> > address@hidden>; Igor Mammedov <address@hidden>;
> > Chen, Yingwen <address@hidden>; Nakajima, Jun
> > <address@hidden>; Boris Ostrovsky
> > <address@hidden>; Joao Marcal Lemos Martins
> > <address@hidden>; Phillip Goerl
> > <address@hidden>
> > Subject: Re: [edk2-rfc] [edk2-devel] CPU hotplug using
> > SMM with QEMU+OVMF
> >
> > On 23/08/19 00:32, Kinney, Michael D wrote:
> > > Paolo,
> > >
> > > It is my understanding that real HW hot plug uses the
> > SDM defined
> > > methods.  Meaning the initial SMI is to 3000:8000 and
> > they rebase to
> > > TSEG in the first SMI.  They must have chipset specific
> > methods to
> > > protect 3000:8000 from DMA.
> >
> > It would be great if you could check.
> >
> > > Can we add a chipset feature to prevent DMA to 64KB
> > range from
> > > 0x30000-0x3FFFF and the UEFI Memory Map and ACPI
> > content can be
> > > updated so the Guest OS knows to not use that range for
> > DMA?
> >
> > If real hardware does it at the chipset level, we will
> > probably use Igor's suggestion of aliasing A-seg to
> > 3000:0000.  Before starting the new CPU, the SMI handler
> > can prepare the SMBASE relocation trampoline at
> > A000:8000 and the hot-plugged CPU will find it at
> > 3000:8000 when it receives the initial SMI.  Because this
> > is backed by RAM at 0xA0000-0xAFFFF, DMA cannot access it
> > and would still go through to RAM at 0x30000.
> >
> > Paolo