Re: [RFC 17/37] DOCUMENTATION: protvirt: Instruction emulation

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Thu, 14 Nov 2019 16:15:26 +0100
Cornelia Huck <cohuck@xxxxxxxxxx> wrote:

> On Thu, 24 Oct 2019 07:40:39 -0400
> Janosch Frank <frankja@xxxxxxxxxxxxx> wrote:
> 
> > As guest memory is inaccessible and information about the guest's
> > state is very limited, new ways for instruction emulation have been
> > introduced.
> > 
> > With a bounce area for guest GRs and instruction data, guest state
> > leaks can be limited by the Ultravisor. KVM now has to move
> > instruction input and output through these areas.
> > 
> > Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
> > ---
> >  Documentation/virtual/kvm/s390-pv.txt | 47
> > +++++++++++++++++++++++++++ 1 file changed, 47 insertions(+)
> > 
> > diff --git a/Documentation/virtual/kvm/s390-pv.txt
> > b/Documentation/virtual/kvm/s390-pv.txt index
> > e09f2dc5f164..cb08d78a7922 100644 ---
> > a/Documentation/virtual/kvm/s390-pv.txt +++
> > b/Documentation/virtual/kvm/s390-pv.txt @@ -48,3 +48,50 @@
> > interception codes have been introduced. One which tells us that
> > CRs have changed. And one for PSW bit 13 changes. The CRs and the
> > PSW in the state description only contain the mask bits and no
> > further info like the current instruction address. +
> > +
> > +Instruction emulation:
> > +With the format 4 state description the SIE instruction already  
> 
> s/description/description,/
> 
> > +interprets more instructions than it does with format 2. As it is
> > not +able to interpret all instruction, the SIE and the UV
> > safeguard KVM's  
> 
> s/instruction/instructions/
> 
> > +emulation inputs and outputs.
> > +
> > +Guest GRs and most of the instruction data, like IO data
> > structures  
> 
> Hm, what 'IO data structures'?

the various IRB and ORB of I/O instructions

> > +are filtered. Instruction data is copied to and from the Secure
> > +Instruction Data Area. Guest GRs are put into / retrieved from the
> > +Interception-Data block.
> > +
> > +The Interception-Data block from the state description's offset
> > 0x380 +contains GRs 0 - 16. Only GR values needed to emulate an
> > instruction +will be copied into this area.
> > +
> > +The Interception Parameters state description field still contains
> > the +the bytes of the instruction text but with pre-set register
> > +values. I.e. each instruction always uses the same instruction
> > text, +to not leak guest instruction text.
> > +
> > +The Secure Instruction Data Area contains instruction storage
> > +data. Data for diag 500 is exempt from that and has to be moved
> > +through shared buffers to KVM.  
> 
> I find this paragraph a bit confusing. What does that imply for diag
> 500 interception? Data is still present in gprs 1-4?

no registers are leaked in the registers. registers are always only
exposed through the state description.

> (Also, why only diag 500? Because it is the 'reserved for kvm'
> diagnose call?)
> 
> > +
> > +When SIE intercepts an instruction, it will only allow data and
> > +program interrupts for this instruction to be moved to the guest
> > via +the two data areas discussed before. Other data is ignored or
> > results +in validity interceptions.
> > +
> > +
> > +Instruction emulation interceptions:
> > +There are two types of SIE secure instruction intercepts. The
> > normal +and the notification type. Normal secure instruction
> > intercepts will +make the guest pending for instruction completion
> > of the intercepted +instruction type, i.e. on SIE entry it is
> > attempted to complete +emulation of the instruction with the data
> > provided by KVM. That might +be a program exception or instruction
> > completion. +
> > +The notification type intercepts inform KVM about guest environment
> > +changes due to guest instruction interpretation. Such an
> > interception  
> 
> 'interpretation by SIE' ?
> 
> > +is recognized for the store prefix instruction and provides the new
> > +lowcore location for mapping change notification arming. Any KVM
> > data +in the data areas is ignored, program exceptions are not
> > injected and +execution continues on next SIE entry, as if no
> > intercept had +happened.  
> 




[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [Kernel Development]     [Kernel Newbies]     [IDE]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite Info]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux ATA RAID]     [Samba]     [Linux Media]     [Device Mapper]

  Powered by Linux