[PATCH v5 4/6] sev/i386: Don't allow a system reset under an SEV-ES guest

[Tom Lendacky]

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>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.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        |  7 +++++--
 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, 58 insertions(+), 2 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 9db74b465e..9ac44ad018 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2411,6 +2411,11 @@ 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 636aab0add..7b4f212d19 100644
--- a/softmmu/runstate.c
+++ b/softmmu/runstate.c
@@ -523,8 +523,11 @@ void qemu_system_guest_crashloaded(GuestPanicInformation 
*info)
 
 void qemu_system_reset_request(ShutdownCause reason)
 {
-    if (reboot_action == REBOOT_ACTION_SHUTDOWN &&
-        reason != SHUTDOWN_CAUSE_SUBSYSTEM_RESET) {
+    if (!cpus_are_resettable()) {
+        error_report("cpus are not resettable, terminating");
+        shutdown_requested = reason;
+    } else if (reboot_action == REBOOT_ACTION_SHUTDOWN &&
+               reason != SHUTDOWN_CAUSE_SUBSYSTEM_RESET) {
         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 477692566a..a907c59c5e 100644
--- a/target/mips/kvm.c
+++ b/target/mips/kvm.c
@@ -1289,3 +1289,8 @@ 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 b8385e6b95..5c5ba801f1 100644
--- a/target/s390x/kvm.c
+++ b/target/s390x/kvm.c
@@ -2601,3 +2601,8 @@ 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