Re: [PATCH v7 02/13] confidential guest support: Introduce new confidential guest support class

[Daniel P . Berrangé]

On Thu, Jan 14, 2021 at 10:58:00AM +1100, David Gibson wrote:
> Several architectures have mechanisms which are designed to protect guest
> memory from interference or eavesdropping by a compromised hypervisor.  AMD
> SEV does this with in-chip memory encryption and Intel's MKTME can do
> similar things.  POWER's Protected Execution Framework (PEF) accomplishes a
> similar goal using an ultravisor and new memory protection features,
> instead of encryption.
> 
> To (partially) unify handling for these, this introduces a new
> ConfidentialGuestSupport QOM base class.  "Confidential" is kind of vague,
> but "confidential computing" seems to be the buzzword about these schemes,
> and "secure" or "protected" are often used in connection to unrelated
> things (such as hypervisor-from-guest or guest-from-guest security).
> 
> The "support" in the name is significant because in at least some of the
> cases it requires the guest to take specific actions in order to protect
> itself from hypervisor eavesdropping.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  backends/confidential-guest-support.c     | 33 ++++++++++++++++++++
>  backends/meson.build                      |  1 +
>  include/exec/confidential-guest-support.h | 38 +++++++++++++++++++++++
>  include/qemu/typedefs.h                   |  1 +
>  target/i386/sev.c                         |  3 +-
>  5 files changed, 75 insertions(+), 1 deletion(-)
>  create mode 100644 backends/confidential-guest-support.c
>  create mode 100644 include/exec/confidential-guest-support.h
> 
> diff --git a/backends/confidential-guest-support.c 
> b/backends/confidential-guest-support.c
> new file mode 100644
> index 0000000000..9b0ded0db4
> --- /dev/null
> +++ b/backends/confidential-guest-support.c
> @@ -0,0 +1,33 @@
> +/*
> + * QEMU Confidential Guest support
> + *
> + * Copyright: David Gibson, Red Hat Inc. 2020
> + *
> + * Authors:
> + *  David Gibson <david@gibson.dropbear.id.au>
> + *
> + * 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 "exec/confidential-guest-support.h"
> +
> +OBJECT_DEFINE_ABSTRACT_TYPE(ConfidentialGuestSupport,
> +                            confidential_guest_support,
> +                            CONFIDENTIAL_GUEST_SUPPORT,
> +                            OBJECT)
> +
> +static void confidential_guest_support_class_init(ObjectClass *oc, void 
> *data)
> +{
> +}
> +
> +static void confidential_guest_support_init(Object *obj)
> +{
> +}
> +
> +static void confidential_guest_support_finalize(Object *obj)
> +{
> +}
> diff --git a/backends/meson.build b/backends/meson.build
> index 484456ece7..d4221831fc 100644
> --- a/backends/meson.build
> +++ b/backends/meson.build
> @@ -6,6 +6,7 @@ softmmu_ss.add([files(
>    'rng-builtin.c',
>    'rng-egd.c',
>    'rng.c',
> +  'confidential-guest-support.c',
>  ), numa])
>  
>  softmmu_ss.add(when: 'CONFIG_POSIX', if_true: files('rng-random.c'))
> diff --git a/include/exec/confidential-guest-support.h 
> b/include/exec/confidential-guest-support.h
> new file mode 100644
> index 0000000000..5f131023ba
> --- /dev/null
> +++ b/include/exec/confidential-guest-support.h
> @@ -0,0 +1,38 @@
> +/*
> + * QEMU Confidential Guest support
> + *   This interface describes the common pieces between various
> + *   schemes for protecting guest memory or other state against a
> + *   compromised hypervisor.  This includes memory encryption (AMD's
> + *   SEV and Intel's MKTME) or special protection modes (PEF on POWER,
> + *   or PV on s390x).
> + *
> + * Copyright: David Gibson, Red Hat Inc. 2020
> + *
> + * Authors:
> + *  David Gibson <david@gibson.dropbear.id.au>
> + *
> + * 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 QEMU_CONFIDENTIAL_GUEST_SUPPORT_H
> +#define QEMU_CONFIDENTIAL_GUEST_SUPPORT_H
> +
> +#ifndef CONFIG_USER_ONLY
> +
> +#include "qom/object.h"
> +
> +#define TYPE_CONFIDENTIAL_GUEST_SUPPORT "confidential-guest-support"
> +OBJECT_DECLARE_SIMPLE_TYPE(ConfidentialGuestSupport, 
> CONFIDENTIAL_GUEST_SUPPORT)
> +
> +struct ConfidentialGuestSupport {
> +    Object parent;
> +};
> +
> +typedef struct ConfidentialGuestSupportClass {
> +    ObjectClass parent;
> +} ConfidentialGuestSupportClass;
> +
> +#endif /* !CONFIG_USER_ONLY */
> +
> +#endif /* QEMU_CONFIDENTIAL_GUEST_SUPPORT_H */
> diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
> index 976b529dfb..33685c79ed 100644
> --- a/include/qemu/typedefs.h
> +++ b/include/qemu/typedefs.h
> @@ -36,6 +36,7 @@ typedef struct BusState BusState;
>  typedef struct Chardev Chardev;
>  typedef struct CompatProperty CompatProperty;
>  typedef struct CoMutex CoMutex;
> +typedef struct ConfidentialGuestSupport ConfidentialGuestSupport;
>  typedef struct CPUAddressSpace CPUAddressSpace;
>  typedef struct CPUState CPUState;
>  typedef struct DeviceListener DeviceListener;
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index 1546606811..6b49925f51 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -31,6 +31,7 @@
>  #include "qom/object.h"
>  #include "exec/address-spaces.h"
>  #include "monitor/monitor.h"
> +#include "exec/confidential-guest-support.h"
>  
>  #define TYPE_SEV_GUEST "sev-guest"
>  OBJECT_DECLARE_SIMPLE_TYPE(SevGuestState, SEV_GUEST)
> @@ -322,7 +323,7 @@ sev_guest_instance_init(Object *obj)
>  
>  /* sev guest info */
>  static const TypeInfo sev_guest_info = {
> -    .parent = TYPE_OBJECT,
> +    .parent = TYPE_CONFIDENTIAL_GUEST_SUPPORT,

If you're changing the parent QOM type, then you also need to change
the parent struct field type in SevguestState to match

>      .name = TYPE_SEV_GUEST,
>      .instance_size = sizeof(SevGuestState),
>      .instance_finalize = sev_guest_finalize,

Regards,
Daniel
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