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

[Greg Kurz]

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() ?

> +
> +
> +#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)
>  {