Re: [PATCH v7 10/13] spapr: Add PEF based confidential guest support

[David Gibson]

On Thu, Jan 14, 2021 at 11:39:11AM +0100, Greg Kurz wrote:
> On Thu, 14 Jan 2021 10:58:08 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > Some upcoming POWER machines have a system called PEF (Protected
> > Execution Facility) which uses a small ultravisor to allow guests to
> > run in a way that they can't be eavesdropped by the hypervisor.  The
> > effect is roughly similar to AMD SEV, although the mechanisms are
> > quite different.
> > 
> > Most of the work of this is done between the guest, KVM and the
> > ultravisor, with little need for involvement by qemu.  However qemu
> > does need to tell KVM to allow secure VMs.
> > 
> > Because the availability of secure mode is a guest visible difference
> > which depends on having the right hardware and firmware, we don't
> > enable this by default.  In order to run a secure guest you need to
> > create a "pef-guest" object and set the confidential-guest-support
> > property to point to it.
> > 
> > Note that this just *allows* secure guests, the architecture of PEF is
> > such that the guest still needs to talk to the ultravisor to enter
> > secure mode.  Qemu has no directl way of knowing if the guest is in
> 
> typo "directl" missed in V6... sorry.
> 
> > secure mode, and certainly can't know until well after machine
> > creation time.
> > 
> > To start a PEF-capable guest, use the command line options:
> >     -object pef-guest,id=pef0 -machine confidential-guest-support=pef0
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  docs/confidential-guest-support.txt |   3 +
> >  docs/papr-pef.txt                   |  30 +++++++
> >  hw/ppc/meson.build                  |   1 +
> >  hw/ppc/pef.c                        | 119 ++++++++++++++++++++++++++++
> >  hw/ppc/spapr.c                      |   6 ++
> >  include/hw/ppc/pef.h                |  25 ++++++
> >  target/ppc/kvm.c                    |  18 -----
> >  target/ppc/kvm_ppc.h                |   6 --
> >  8 files changed, 184 insertions(+), 24 deletions(-)
> >  create mode 100644 docs/papr-pef.txt
> >  create mode 100644 hw/ppc/pef.c
> >  create mode 100644 include/hw/ppc/pef.h
> > 
> > diff --git a/docs/confidential-guest-support.txt 
> > b/docs/confidential-guest-support.txt
> > index 2790425b38..f0801814ff 100644
> > --- a/docs/confidential-guest-support.txt
> > +++ b/docs/confidential-guest-support.txt
> > @@ -40,4 +40,7 @@ Currently supported confidential guest mechanisms are:
> >  AMD Secure Encrypted Virtualization (SEV)
> >      docs/amd-memory-encryption.txt
> >  
> > +POWER Protected Execution Facility (PEF)
> > +    docs/papr-pef.txt
> > +
> >  Other mechanisms may be supported in future.
> > diff --git a/docs/papr-pef.txt b/docs/papr-pef.txt
> > new file mode 100644
> > index 0000000000..6419e995cf
> > --- /dev/null
> > +++ b/docs/papr-pef.txt
> > @@ -0,0 +1,30 @@
> > +POWER (PAPR) Protected Execution Facility (PEF)
> > +===============================================
> > +
> > +Protected Execution Facility (PEF), also known as Secure Guest support
> > +is a feature found on IBM POWER9 and POWER10 processors.
> > +
> > +If a suitable firmware including an Ultravisor is installed, it adds
> > +an extra memory protection mode to the CPU.  The ultravisor manages a
> > +pool of secure memory which cannot be accessed by the hypervisor.
> > +
> > +When this feature is enabled in qemu, a guest can use ultracalls to
> > +enter "secure mode".  This transfers most of its memory to secure
> > +memory, where it cannot be eavesdropped by a compromised hypervisor.
> > +
> > +Launching
> > +---------
> > +
> > +To launch a guest which will be permitted to enter PEF secure mode:
> > +
> > +# ${QEMU} \
> > +    -object pef-guest,id=pef0 \
> > +    -machine confidential-guest-support=pef0 \
> > +    ...
> > +
> > +Live Migration
> > +----------------
> > +
> > +Live migration is not yet implemented for PEF guests.  For
> > +consistency, we currently prevent migration if the PEF feature is
> > +enabled, whether or not the guest has actually entered secure mode.
> > diff --git a/hw/ppc/meson.build b/hw/ppc/meson.build
> > index ffa2ec37fa..218631c883 100644
> > --- a/hw/ppc/meson.build
> > +++ b/hw/ppc/meson.build
> > @@ -27,6 +27,7 @@ ppc_ss.add(when: 'CONFIG_PSERIES', if_true: files(
> >    'spapr_nvdimm.c',
> >    'spapr_rtas_ddw.c',
> >    'spapr_numa.c',
> > +  'pef.c',
> >  ))
> >  ppc_ss.add(when: 'CONFIG_SPAPR_RNG', if_true: files('spapr_rng.c'))
> >  ppc_ss.add(when: ['CONFIG_PSERIES', 'CONFIG_LINUX'], if_true: files(
> > diff --git a/hw/ppc/pef.c b/hw/ppc/pef.c
> > new file mode 100644
> > index 0000000000..02b9b3b460
> > --- /dev/null
> > +++ b/hw/ppc/pef.c
> > @@ -0,0 +1,119 @@
> > +/*
> > + * PEF (Protected Execution Facility) for POWER support
> > + *
> > + * Copyright David Gibson, Redhat Inc. 2020
> > + *
> > + * This work is licensed under the terms of the GNU GPL, version 2 or 
> > later.
> > + * See the COPYING file in the top-level directory.
> > + *
> > + */
> > +
> > +#include "qemu/osdep.h"
> > +
> > +#include "qapi/error.h"
> > +#include "qom/object_interfaces.h"
> > +#include "sysemu/kvm.h"
> > +#include "migration/blocker.h"
> > +#include "exec/confidential-guest-support.h"
> > +#include "hw/ppc/pef.h"
> > +
> > +#define TYPE_PEF_GUEST "pef-guest"
> > +OBJECT_DECLARE_SIMPLE_TYPE(PefGuest, PEF_GUEST)
> > +
> > +typedef struct PefGuest PefGuest;
> > +typedef struct PefGuestClass PefGuestClass;
> > +
> > +struct PefGuestClass {
> > +    ConfidentialGuestSupportClass parent_class;
> > +};
> > +
> > +/**
> > + * PefGuest:
> > + *
> > + * The PefGuest object is used for creating and managing a PEF
> > + * guest.
> > + *
> > + * # $QEMU \
> > + *         -object pef-guest,id=pef0 \
> > + *         -machine ...,confidential-guest-support=pef0
> > + */
> > +struct PefGuest {
> > +    ConfidentialGuestSupport parent_obj;
> > +};
> > +
> > +#ifdef CONFIG_KVM
> > +static int kvmppc_svm_init(Error **errp)
> > +{
> > +    if (!kvm_check_extension(kvm_state, KVM_CAP_PPC_SECURE_GUEST)) {
> > +        error_setg(errp,
> > +                   "KVM implementation does not support Secure VMs (is an 
> > ultravisor running?)");
> > +        return -1;
> > +    } else {
> > +        int ret = kvm_vm_enable_cap(kvm_state, KVM_CAP_PPC_SECURE_GUEST, 
> > 0, 1);
> > +
> > +        if (ret < 0) {
> > +            error_setg(errp,
> > +                       "Error enabling PEF with KVM");
> > +            return -1;
> > +        }
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> > +/*
> > + * Don't set error if KVM_PPC_SVM_OFF ioctl is invoked on kernels
> > + * that don't support this ioctl.
> > + */
> > +void kvmppc_svm_off(Error **errp)
> > +{
> > +    int rc;
> > +
> > +    if (!kvm_enabled()) {
> > +        return;
> > +    }
> > +
> > +    rc = kvm_vm_ioctl(KVM_STATE(current_accel()), KVM_PPC_SVM_OFF);
> > +    if (rc && rc != -ENOTTY) {
> > +        error_setg_errno(errp, -rc, "KVM_PPC_SVM_OFF ioctl failed");
> > +    }
> > +}
> > +#else
> > +static int kvmppc_svm_init(Error **errp)
> > +{
> > +    g_assert_not_reached();
> > +}
> > +#endif
> > +
> > +int pef_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
> > +{
> > +    if (!object_dynamic_cast(OBJECT(cgs), TYPE_PEF_GUEST)) {
> > +        return 0;
> > +    }
> > +
> > +    if (!kvm_enabled()) {
> > +        error_setg(errp, "PEF requires KVM");
> > +        return -1;
> > +    }
> > +
> > +    return kvmppc_svm_init(errp);
> > +}
> > +
> > +OBJECT_DEFINE_TYPE_WITH_INTERFACES(PefGuest,
> > +                                   pef_guest,
> > +                                   PEF_GUEST,
> > +                                   CONFIDENTIAL_GUEST_SUPPORT,
> > +                                   { TYPE_USER_CREATABLE },
> > +                                   { NULL })
> > +
> > +static void pef_guest_class_init(ObjectClass *oc, void *data)
> > +{
> > +}
> > +
> > +static void pef_guest_init(Object *obj)
> > +{
> > +}
> > +
> > +static void pef_guest_finalize(Object *obj)
> > +{
> > +}
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 2c403b574e..accf7a834b 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -83,6 +83,7 @@
> >  #include "hw/ppc/spapr_tpm_proxy.h"
> >  #include "hw/ppc/spapr_nvdimm.h"
> >  #include "hw/ppc/spapr_numa.h"
> > +#include "hw/ppc/pef.h"
> >  
> >  #include "monitor/monitor.h"
> >  
> > @@ -2658,6 +2659,11 @@ static void spapr_machine_init(MachineState *machine)
> >      char *filename;
> >      Error *resize_hpt_err = NULL;
> >  
> > +    /*
> > +     * if Secure VM (PEF) support is configured, then initialize it
> > +     */
> > +    pef_kvm_init(machine->cgs, &error_fatal);
> > +
> >      msi_nonbroken = true;
> >  
> >      QLIST_INIT(&spapr->phbs);
> > diff --git a/include/hw/ppc/pef.h b/include/hw/ppc/pef.h
> > new file mode 100644
> > index 0000000000..57d4ec9fe6
> > --- /dev/null
> > +++ b/include/hw/ppc/pef.h
> > @@ -0,0 +1,25 @@
> > +/*
> > + * PEF (Protected Execution Facility) for POWER support
> > + *
> > + * Copyright David Gibson, Redhat Inc. 2020
> > + *
> > + * This work is licensed under the terms of the GNU GPL, version 2 or 
> > later.
> > + * See the COPYING file in the top-level directory.
> > + *
> > + */
> > +
> > +#ifndef HW_PPC_PEF_H
> > +#define HW_PPC_PEF_H
> > +
> > +int pef_kvm_init(ConfidentialGuestSupport *cgs, Error **errp);
> > +
> > +#ifdef CONFIG_KVM
> > +void kvmppc_svm_off(Error **errp);
> > +#else
> > +static inline void kvmppc_svm_off(Error **errp)
> > +{
> > +}
> > +#endif
> 
> The API seems a bit inconsistent. On one side, we have pef_kvm_init()
> which hides all the implementation details (including KVM stubs) in
> the C file. And on the other side, we expose kvmppc_svm_off() to
> the machine code... Especially, I was expecting to see a
> g_assert_not_reached() in the kvmppc_svm_off() stub, just like
> kvmppc_svm_init().
> 
> Maybe introduce an intermediate pef_kvm_off() API, that matches
> what pef_kvm_init() does with kvmppc_svm_init() ?

Fair enough.  I've revised this for the next spin.

> 
> > +
> > +
> > +#endif /* HW_PPC_PEF_H */
> > diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> > index daf690a678..0c5056dd5b 100644
> > --- a/target/ppc/kvm.c
> > +++ b/target/ppc/kvm.c
> > @@ -2929,21 +2929,3 @@ void kvmppc_set_reg_tb_offset(PowerPCCPU *cpu, 
> > int64_t tb_offset)
> >          kvm_set_one_reg(cs, KVM_REG_PPC_TB_OFFSET, &tb_offset);
> >      }
> >  }
> > -
> > -/*
> > - * Don't set error if KVM_PPC_SVM_OFF ioctl is invoked on kernels
> > - * that don't support this ioctl.
> > - */
> > -void kvmppc_svm_off(Error **errp)
> > -{
> > -    int rc;
> > -
> > -    if (!kvm_enabled()) {
> > -        return;
> > -    }
> > -
> > -    rc = kvm_vm_ioctl(KVM_STATE(current_accel()), KVM_PPC_SVM_OFF);
> > -    if (rc && rc != -ENOTTY) {
> > -        error_setg_errno(errp, -rc, "KVM_PPC_SVM_OFF ioctl failed");
> > -    }
> > -}
> > diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
> > index 73ce2bc951..989f61ace0 100644
> > --- a/target/ppc/kvm_ppc.h
> > +++ b/target/ppc/kvm_ppc.h
> > @@ -39,7 +39,6 @@ int kvmppc_booke_watchdog_enable(PowerPCCPU *cpu);
> >  target_ulong kvmppc_configure_v3_mmu(PowerPCCPU *cpu,
> >                                       bool radix, bool gtse,
> >                                       uint64_t proc_tbl);
> > -void kvmppc_svm_off(Error **errp);
> >  #ifndef CONFIG_USER_ONLY
> >  bool kvmppc_spapr_use_multitce(void);
> >  int kvmppc_spapr_enable_inkernel_multitce(void);
> > @@ -216,11 +215,6 @@ static inline target_ulong 
> > kvmppc_configure_v3_mmu(PowerPCCPU *cpu,
> >      return 0;
> >  }
> >  
> > -static inline void kvmppc_svm_off(Error **errp)
> > -{
> > -    return;
> > -}
> > -
> >  static inline void kvmppc_set_reg_ppc_online(PowerPCCPU *cpu,
> >                                               unsigned int online)
> >  {
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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