Re: [PATCH v3 4/5] sev/i386: Don't allow a system reset under an SEV-ES guest

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

On 9/17/20 12:01 PM, Dr. David Alan Gilbert wrote:
> * Tom Lendacky (thomas.lendacky@xxxxxxx) wrote:
> > From: Tom Lendacky <thomas.lendacky@xxxxxxx>
> >
> > An SEV-ES guest does not allow register state to be altered once it has
> > been measured. When a SEV-ES guest issues a reboot command, Qemu will
> > reset the vCPU state and resume the guest. This will cause failures under
> > SEV-ES, so prevent that from occurring.
> >
> > Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > ---
> >   accel/kvm/kvm-all.c       | 9 +++++++++
> >   include/sysemu/cpus.h     | 2 ++
> >   include/sysemu/hw_accel.h | 5 +++++
> >   include/sysemu/kvm.h      | 2 ++
> >   softmmu/cpus.c            | 5 +++++
> >   softmmu/vl.c              | 5 ++++-
> >   6 files changed, 27 insertions(+), 1 deletion(-)
> >
> > diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> > index 20725b0368..63153b6e53 100644
> > --- a/accel/kvm/kvm-all.c
> > +++ b/accel/kvm/kvm-all.c
> > @@ -2388,6 +2388,15 @@ void kvm_flush_coalesced_mmio_buffer(void)
> >       s->coalesced_flush_in_progress = false;
> >   }
> >   
> > +bool kvm_cpu_check_resettable(void)
> > +{
> > +    /*
> > +     * If we have a valid reset vector override, then SEV-ES is active
> > +     * and the CPU can't be reset.
> > +     */
> > +    return !kvm_state->reset_valid;
>
> This seems a bit weird since it's in generic rather than x86 specific
> code.

I could push it down to arch specific code. Is there a way to do that 
without defining the function for all the other arches?

Thanks,
Tom

> Dave
>
> > +}
> > +
> >   static void do_kvm_cpu_synchronize_state(CPUState *cpu, run_on_cpu_data arg)
> >   {
> >       if (!cpu->vcpu_dirty) {
> > diff --git a/include/sysemu/cpus.h b/include/sysemu/cpus.h
> > index 3c1da6a018..6d688c757f 100644
> > --- a/include/sysemu/cpus.h
> > +++ b/include/sysemu/cpus.h
> > @@ -24,6 +24,8 @@ void dump_drift_info(void);
> >   void qemu_cpu_kick_self(void);
> >   void qemu_timer_notify_cb(void *opaque, QEMUClockType type);
> >   
> > +bool cpu_is_resettable(void);
> > +
> >   void cpu_synchronize_all_states(void);
> >   void cpu_synchronize_all_post_reset(void);
> >   void cpu_synchronize_all_post_init(void);
> > diff --git a/include/sysemu/hw_accel.h b/include/sysemu/hw_accel.h
> > index e128f8b06b..8b4536e7ae 100644
> > --- a/include/sysemu/hw_accel.h
> > +++ b/include/sysemu/hw_accel.h
> > @@ -17,6 +17,11 @@
> >   #include "sysemu/hvf.h"
> >   #include "sysemu/whpx.h"
> >   
> > +static inline bool cpu_check_resettable(void)
> > +{
> > +    return kvm_enabled() ? kvm_cpu_check_resettable() : true;
> > +}
> > +
> >   static inline void cpu_synchronize_state(CPUState *cpu)
> >   {
> >       if (kvm_enabled()) {
> > diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> > index f74cfa85ab..eb94bbbff9 100644
> > --- a/include/sysemu/kvm.h
> > +++ b/include/sysemu/kvm.h
> > @@ -494,6 +494,8 @@ int kvm_physical_memory_addr_from_host(KVMState *s, void *ram_addr,
> >   
> >   #endif /* NEED_CPU_H */
> >   
> > +bool kvm_cpu_check_resettable(void);
> > +
> >   void kvm_cpu_synchronize_state(CPUState *cpu);
> >   void kvm_cpu_synchronize_post_reset(CPUState *cpu);
> >   void kvm_cpu_synchronize_post_init(CPUState *cpu);
> > diff --git a/softmmu/cpus.c b/softmmu/cpus.c
> > index a802e899ab..32f286643f 100644
> > --- a/softmmu/cpus.c
> > +++ b/softmmu/cpus.c
> > @@ -927,6 +927,11 @@ void hw_error(const char *fmt, ...)
> >       abort();
> >   }
> >   
> > +bool cpu_is_resettable(void)
> > +{
> > +    return cpu_check_resettable();
> > +}
> > +
> >   void cpu_synchronize_all_states(void)
> >   {
> >       CPUState *cpu;
> > diff --git a/softmmu/vl.c b/softmmu/vl.c
> > index 4eb9d1f7fd..422fbb1650 100644
> > --- a/softmmu/vl.c
> > +++ b/softmmu/vl.c
> > @@ -1475,7 +1475,10 @@ void qemu_system_guest_crashloaded(GuestPanicInformation *info)
> >   
> >   void qemu_system_reset_request(ShutdownCause reason)
> >   {
> > -    if (no_reboot && reason != SHUTDOWN_CAUSE_SUBSYSTEM_RESET) {
> > +    if (!cpu_is_resettable()) {
> > +        error_report("cpus are not resettable, terminating");
> > +        shutdown_requested = reason;
> > +    } else if (no_reboot && reason != SHUTDOWN_CAUSE_SUBSYSTEM_RESET) {
> >           shutdown_requested = reason;
> >       } else {
> >           reset_requested = reason;
> > --
> > 2.28.0