Re: [PATCH v8 07/13] confidential guest support: Introduce cgs "ready" flag

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Feb 10, 2021 at 10:25:30AM -0600, Venu Busireddy wrote:
> On 2021-02-02 15:13:09 +1100, David Gibson wrote:
> > The platform specific details of mechanisms for implementing
> > confidential guest support may require setup at various points during
> > initialization.  Thus, it's not really feasible to have a single cgs
> > initialization hook, but instead each mechanism needs its own
> > initialization calls in arch or machine specific code.
> > 
> > However, to make it harder to have a bug where a mechanism isn't
> > properly initialized under some circumstances, we want to have a
> > common place, late in boot, where we verify that cgs has been
> > initialized if it was requested.
> > 
> > This patch introduces a ready flag to the ConfidentialGuestSupport
> > base type to accomplish this, which we verify in
> > qemu_machine_creation_done().
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > Reviewed-by: Greg Kurz <groug@kaod.org>
> > ---
> >  include/exec/confidential-guest-support.h | 24 +++++++++++++++++++++++
> >  softmmu/vl.c                              | 10 ++++++++++
> >  target/i386/sev.c                         |  2 ++
> >  3 files changed, 36 insertions(+)
> > 
> > diff --git a/include/exec/confidential-guest-support.h b/include/exec/confidential-guest-support.h
> > index 3db6380e63..5dcf602047 100644
> > --- a/include/exec/confidential-guest-support.h
> > +++ b/include/exec/confidential-guest-support.h
> > @@ -27,6 +27,30 @@ OBJECT_DECLARE_SIMPLE_TYPE(ConfidentialGuestSupport, CONFIDENTIAL_GUEST_SUPPORT)
> >  
> >  struct ConfidentialGuestSupport {
> >      Object parent;
> > +
> > +    /*
> > +     * ready: flag set by CGS initialization code once it's ready to
> > +     *        start executing instructions in a potentially-secure
> > +     *        guest
> > +     *
> > +     * The definition here is a bit fuzzy, because this is essentially
> > +     * part of a self-sanity-check, rather than a strict mechanism.
> > +     *
> > +     * It's not fasible to have a single point in the common machine
> 
> Just a nit pick.
> 
> s/fasible/feasible/

Already fixed in the version that got merged.

> > +     * init path to configure confidential guest support, because
> > +     * different mechanisms have different interdependencies requiring
> > +     * initialization in different places, often in arch or machine
> > +     * type specific code.  It's also usually not possible to check
> > +     * for invalid configurations until that initialization code.
> > +     * That means it would be very easy to have a bug allowing CGS
> > +     * init to be bypassed entirely in certain configurations.
> > +     *
> > +     * Silently ignoring a requested security feature would be bad, so
> > +     * to avoid that we check late in init that this 'ready' flag is
> > +     * set if CGS was requested.  If the CGS init hasn't happened, and
> > +     * so 'ready' is not set, we'll abort.
> > +     */
> > +    bool ready;
> >  };
> >  
> >  typedef struct ConfidentialGuestSupportClass {
> > diff --git a/softmmu/vl.c b/softmmu/vl.c
> > index 1b464e3474..1869ed54a9 100644
> > --- a/softmmu/vl.c
> > +++ b/softmmu/vl.c
> > @@ -101,6 +101,7 @@
> >  #include "qemu/plugin.h"
> >  #include "qemu/queue.h"
> >  #include "sysemu/arch_init.h"
> > +#include "exec/confidential-guest-support.h"
> >  
> >  #include "ui/qemu-spice.h"
> >  #include "qapi/string-input-visitor.h"
> > @@ -2497,6 +2498,8 @@ static void qemu_create_cli_devices(void)
> >  
> >  static void qemu_machine_creation_done(void)
> >  {
> > +    MachineState *machine = MACHINE(qdev_get_machine());
> > +
> >      /* Did we create any drives that we failed to create a device for? */
> >      drive_check_orphaned();
> >  
> > @@ -2516,6 +2519,13 @@ static void qemu_machine_creation_done(void)
> >  
> >      qdev_machine_creation_done();
> >  
> > +    if (machine->cgs) {
> > +        /*
> > +         * Verify that Confidential Guest Support has actually been initialized
> > +         */
> > +        assert(machine->cgs->ready);
> > +    }
> > +
> >      if (foreach_device_config(DEV_GDB, gdbserver_start) < 0) {
> >          exit(1);
> >      }
> > diff --git a/target/i386/sev.c b/target/i386/sev.c
> > index 590cb31fa8..f9e9b5d8ae 100644
> > --- a/target/i386/sev.c
> > +++ b/target/i386/sev.c
> > @@ -737,6 +737,8 @@ int sev_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
> >      qemu_add_machine_init_done_notifier(&sev_machine_done_notify);
> >      qemu_add_vm_change_state_handler(sev_vm_state_change, sev);
> >  
> > +    cgs->ready = true;
> > +
> >      return 0;
> >  err:
> >      sev_guest = NULL;
> 

-- 
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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