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

[Tom Lendacky <thomas.lendacky@amd.com>]

On 9/17/20 12:01 PM, Dr. David Alan Gilbert wrote:
> * Tom Lendacky (thomas.lendacky@amd.com) 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 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@amd.com>
>> ---
>>   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
>>