Re: [PATCH v6 4/6] sev/i386: Don't allow a system reset under an SEV-ES guest

[Venu Busireddy <venu.busireddy@oracle.com>]

On 2021-01-26 11:36:47 -0600, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> 
> An SEV-ES guest does not allow register state to be altered once it has
> been measured. When an SEV-ES guest issues a reboot command, Qemu will
> reset the vCPU state and resume the guest. This will cause failures under
> SEV-ES. Prevent that from occuring by introducing an arch-specific
> callback that returns a boolean indicating whether vCPUs are resettable.
> 
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: Aurelien Jarno <aurelien@aurel32.net>
> Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
> Cc: Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>
> Cc: David Gibson <david@gibson.dropbear.id.au>
> Cc: David Hildenbrand <david@redhat.com>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>

Reviewed-by: Venu Busireddy <venu.busireddy@oracle.com>

> ---
>  accel/kvm/kvm-all.c       |  5 +++++
>  include/sysemu/cpus.h     |  2 ++
>  include/sysemu/hw_accel.h |  5 +++++
>  include/sysemu/kvm.h      | 10 ++++++++++
>  softmmu/cpus.c            |  5 +++++
>  softmmu/runstate.c        |  3 +++
>  target/arm/kvm.c          |  5 +++++
>  target/i386/kvm/kvm.c     |  6 ++++++
>  target/mips/kvm.c         |  5 +++++
>  target/ppc/kvm.c          |  5 +++++
>  target/s390x/kvm.c        |  5 +++++
>  11 files changed, 56 insertions(+)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 410879cf94..6c099a3869 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -2414,6 +2414,11 @@ void kvm_flush_coalesced_mmio_buffer(void)
>      s->coalesced_flush_in_progress = false;
>  }
>  
> +bool kvm_cpu_check_are_resettable(void)
> +{
> +    return kvm_arch_cpu_check_are_resettable();
> +}
> +
>  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 e8156728c6..1cb4f9dbeb 100644
> --- a/include/sysemu/cpus.h
> +++ b/include/sysemu/cpus.h
> @@ -57,6 +57,8 @@ extern int icount_align_option;
>  /* Unblock cpu */
>  void qemu_cpu_kick_self(void);
>  
> +bool cpus_are_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 ffed6192a3..61672f9b32 100644
> --- a/include/sysemu/hw_accel.h
> +++ b/include/sysemu/hw_accel.h
> @@ -22,4 +22,9 @@ void cpu_synchronize_post_reset(CPUState *cpu);
>  void cpu_synchronize_post_init(CPUState *cpu);
>  void cpu_synchronize_pre_loadvm(CPUState *cpu);
>  
> +static inline bool cpu_check_are_resettable(void)
> +{
> +    return kvm_enabled() ? kvm_cpu_check_are_resettable() : true;
> +}
> +
>  #endif /* QEMU_HW_ACCEL_H */
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index 875ca101e3..3e265cea3d 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -573,4 +573,14 @@ int kvm_get_max_memslots(void);
>  /* Notify resamplefd for EOI of specific interrupts. */
>  void kvm_resample_fd_notify(int gsi);
>  
> +/**
> + * kvm_cpu_check_are_resettable - return whether CPUs can be reset
> + *
> + * Returns: true: CPUs are resettable
> + *          false: CPUs are not resettable
> + */
> +bool kvm_cpu_check_are_resettable(void);
> +
> +bool kvm_arch_cpu_check_are_resettable(void);
> +
>  #endif
> diff --git a/softmmu/cpus.c b/softmmu/cpus.c
> index 1dc20b9dc3..89de46eae0 100644
> --- a/softmmu/cpus.c
> +++ b/softmmu/cpus.c
> @@ -194,6 +194,11 @@ void cpu_synchronize_pre_loadvm(CPUState *cpu)
>      }
>  }
>  
> +bool cpus_are_resettable(void)
> +{
> +    return cpu_check_are_resettable();
> +}
> +
>  int64_t cpus_get_virtual_clock(void)
>  {
>      /*
> diff --git a/softmmu/runstate.c b/softmmu/runstate.c
> index beee050815..1813691898 100644
> --- a/softmmu/runstate.c
> +++ b/softmmu/runstate.c
> @@ -527,6 +527,9 @@ void qemu_system_reset_request(ShutdownCause reason)
>      if (reboot_action == REBOOT_ACTION_SHUTDOWN &&
>          reason != SHUTDOWN_CAUSE_SUBSYSTEM_RESET) {
>          shutdown_requested = reason;
> +    } else if (!cpus_are_resettable()) {
> +        error_report("cpus are not resettable, terminating");
> +        shutdown_requested = reason;
>      } else {
>          reset_requested = reason;
>      }
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index ffe186de8d..00e124c812 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -1045,3 +1045,8 @@ int kvm_arch_msi_data_to_gsi(uint32_t data)
>  {
>      return (data - 32) & 0xffff;
>  }
> +
> +bool kvm_arch_cpu_check_are_resettable(void)
> +{
> +    return true;
> +}
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index aaae79557d..bb6bfc19de 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -27,6 +27,7 @@
>  #include "sysemu/kvm_int.h"
>  #include "sysemu/runstate.h"
>  #include "kvm_i386.h"
> +#include "sev_i386.h"
>  #include "hyperv.h"
>  #include "hyperv-proto.h"
>  
> @@ -4788,3 +4789,8 @@ bool kvm_has_waitpkg(void)
>  {
>      return has_msr_umwait;
>  }
> +
> +bool kvm_arch_cpu_check_are_resettable(void)
> +{
> +    return !sev_es_enabled();
> +}
> diff --git a/target/mips/kvm.c b/target/mips/kvm.c
> index 84fb10ea35..123ec1be7e 100644
> --- a/target/mips/kvm.c
> +++ b/target/mips/kvm.c
> @@ -1290,3 +1290,8 @@ int mips_kvm_type(MachineState *machine, const char *vm_type)
>  
>      return -1;
>  }
> +
> +bool kvm_arch_cpu_check_are_resettable(void)
> +{
> +    return true;
> +}
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index daf690a678..f45ed11058 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -2947,3 +2947,8 @@ void kvmppc_svm_off(Error **errp)
>          error_setg_errno(errp, -rc, "KVM_PPC_SVM_OFF ioctl failed");
>      }
>  }
> +
> +bool kvm_arch_cpu_check_are_resettable(void)
> +{
> +    return true;
> +}
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index dc27fa36c9..7a892d663d 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -2599,3 +2599,8 @@ void kvm_s390_stop_interrupt(S390CPU *cpu)
>  
>      kvm_s390_vcpu_interrupt(cpu, &irq);
>  }
> +
> +bool kvm_arch_cpu_check_are_resettable(void)
> +{
> +    return true;
> +}
> -- 
> 2.30.0
>