s390: Recognize confidential-guest-support option

At least some s390 cpu models support "Protected Virtualization" (PV),
a mechanism to protect guests from eavesdropping by a compromised
hypervisor.

This is similar in function to other mechanisms like AMD's SEV and
POWER's PEF, which are controlled by the "confidential-guest-support"
machine option.  s390 is a slightly special case, because we already
supported PV, simply by using a CPU model with the required feature
(S390_FEAT_UNPACK).

To integrate this with the option used by other platforms, we
implement the following compromise:

 - When the confidential-guest-support option is set, s390 will
   recognize it, verify that the CPU can support PV (failing if not)
   and set virtio default options necessary for encrypted or protected
   guests, as on other platforms.  i.e. if confidential-guest-support
   is set, we will either create a guest capable of entering PV mode,
   or fail outright.

 - If confidential-guest-support is not set, guests might still be
   able to enter PV mode, if the CPU has the right model.  This may be
   a little surprising, but shouldn't actually be harmful.

To start a guest supporting Protected Virtualization using the new
option use the command line arguments:
    -object s390-pv-guest,id=pv0 -machine confidential-guest-support=pv0

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
This commit is contained in:
David Gibson 2020-07-23 14:36:45 +10:00
parent 9f88a7a3df
commit 651615d92d
5 changed files with 98 additions and 6 deletions

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@ -43,4 +43,7 @@ AMD Secure Encrypted Virtualization (SEV)
POWER Protected Execution Facility (PEF)
docs/papr-pef.txt
s390x Protected Virtualization (PV)
docs/system/s390x/protvirt.rst
Other mechanisms may be supported in future.

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@ -22,15 +22,22 @@ If those requirements are met, the capability `KVM_CAP_S390_PROTECTED`
will indicate that KVM can support PVMs on that LPAR.
QEMU Settings
-------------
Running a Protected Virtual Machine
-----------------------------------
To indicate to the VM that it can transition into protected mode, the
To run a PVM you will need to select a CPU model which includes the
`Unpack facility` (stfle bit 161 represented by the feature
`unpack`/`S390_FEAT_UNPACK`) needs to be part of the cpu model of
the VM.
`unpack`/`S390_FEAT_UNPACK`), and add these options to the command line::
-object s390-pv-guest,id=pv0 \
-machine confidential-guest-support=pv0
Adding these options will:
* Ensure the `unpack` facility is available
* Enable the IOMMU by default for all I/O devices
* Initialize the PV mechanism
All I/O devices need to use the IOMMU.
Passthrough (vfio) devices are currently not supported.
Host huge page backings are not supported. However guests can use huge

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@ -14,8 +14,11 @@
#include <linux/kvm.h>
#include "cpu.h"
#include "qapi/error.h"
#include "qemu/error-report.h"
#include "sysemu/kvm.h"
#include "qom/object_interfaces.h"
#include "exec/confidential-guest-support.h"
#include "hw/s390x/ipl.h"
#include "hw/s390x/pv.h"
@ -111,3 +114,62 @@ void s390_pv_inject_reset_error(CPUState *cs)
/* Report that we are unable to enter protected mode */
env->regs[r1 + 1] = DIAG_308_RC_INVAL_FOR_PV;
}
#define TYPE_S390_PV_GUEST "s390-pv-guest"
OBJECT_DECLARE_SIMPLE_TYPE(S390PVGuest, S390_PV_GUEST)
/**
* S390PVGuest:
*
* The S390PVGuest object is basically a dummy used to tell the
* confidential guest support system to use s390's PV mechanism.
*
* # $QEMU \
* -object s390-pv-guest,id=pv0 \
* -machine ...,confidential-guest-support=pv0
*/
struct S390PVGuest {
ConfidentialGuestSupport parent_obj;
};
typedef struct S390PVGuestClass S390PVGuestClass;
struct S390PVGuestClass {
ConfidentialGuestSupportClass parent_class;
};
int s390_pv_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
{
if (!object_dynamic_cast(OBJECT(cgs), TYPE_S390_PV_GUEST)) {
return 0;
}
if (!s390_has_feat(S390_FEAT_UNPACK)) {
error_setg(errp,
"CPU model does not support Protected Virtualization");
return -1;
}
cgs->ready = true;
return 0;
}
OBJECT_DEFINE_TYPE_WITH_INTERFACES(S390PVGuest,
s390_pv_guest,
S390_PV_GUEST,
CONFIDENTIAL_GUEST_SUPPORT,
{ TYPE_USER_CREATABLE },
{ NULL })
static void s390_pv_guest_class_init(ObjectClass *oc, void *data)
{
}
static void s390_pv_guest_init(Object *obj)
{
}
static void s390_pv_guest_finalize(Object *obj)
{
}

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@ -250,6 +250,9 @@ static void ccw_init(MachineState *machine)
/* init CPUs (incl. CPU model) early so s390_has_feature() works */
s390_init_cpus(machine);
/* Need CPU model to be determined before we can set up PV */
s390_pv_init(machine->cgs, &error_fatal);
s390_flic_init();
/* init the SIGP facility */

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@ -12,6 +12,9 @@
#ifndef HW_S390_PV_H
#define HW_S390_PV_H
#include "qapi/error.h"
#include "sysemu/kvm.h"
#ifdef CONFIG_KVM
#include "cpu.h"
#include "hw/s390x/s390-virtio-ccw.h"
@ -55,4 +58,18 @@ static inline void s390_pv_unshare(void) {}
static inline void s390_pv_inject_reset_error(CPUState *cs) {};
#endif /* CONFIG_KVM */
int s390_pv_kvm_init(ConfidentialGuestSupport *cgs, Error **errp);
static inline int s390_pv_init(ConfidentialGuestSupport *cgs, Error **errp)
{
if (!cgs) {
return 0;
}
if (kvm_enabled()) {
return s390_pv_kvm_init(cgs, errp);
}
error_setg(errp, "Protected Virtualization requires KVM");
return -1;
}
#endif /* HW_S390_PV_H */