[RFC PATCH] target/ppc: Add capability for enabling secure guests

[Fabiano Rosas]

Making use of ppc's Protected Execution Facility (PEF) feature, a
guest can become a secure guest (aka. secure VM - SVM) and have its
memory protected from access by the host. This feature is mediated by
a piece of firmware called the Ultravisor (UV).

The transition from a regular to a secure VM is initiated by the guest
kernel during prom_init via the use of an ultracall (enter secure mode
- UV_ESM) and with cooperation from the hypervisor via an hcall
(H_SVM_INIT_START).

Currently QEMU has no knowledge of this process and no way to
determine if a host supports the feature. A guest with PEF support
enabled would always try to enter secure mode regardless of user
intent or hardware support.

To address the above, a new KVM capability (KVM_CAP_PPC_SECURE_GUEST
[1]) is being introduced in the kernel without which KVM will block
the secure transition.

This patch adds support for checking/enabling this KVM capability via
a new spapr capability (SPAPR_CAP_SECURE_GUEST) and the equivalent
command line switch (-machine pseries,cap-svm). The capability
defaults to off.

1- https://lore.kernel.org/kvm/20200319043301.GA13052@blackberry

Signed-off-by: Fabiano Rosas <address@hidden>
---

I have implemented this to be able to test Paul's patch. I'm sending
it as RFC in case it helps anyone else and if we decide to go in this
direction I can develop it further.

PS: TCG currently gets in a loop of 0x700 due to the lack of 'sc 2'
emulation - and all the rest of PEF, of course =).

---
 hw/ppc/spapr.c         |  1 +
 hw/ppc/spapr_caps.c    | 30 ++++++++++++++++++++++++++++++
 include/hw/ppc/spapr.h |  3 ++-
 target/ppc/kvm.c       | 12 ++++++++++++
 target/ppc/kvm_ppc.h   | 12 ++++++++++++
 5 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 9a2bd501aa..a881ac4e29 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -4542,6 +4542,7 @@ static void spapr_machine_class_init(ObjectClass *oc, 
void *data)
     smc->default_caps.caps[SPAPR_CAP_LARGE_DECREMENTER] = SPAPR_CAP_ON;
     smc->default_caps.caps[SPAPR_CAP_CCF_ASSIST] = SPAPR_CAP_ON;
     smc->default_caps.caps[SPAPR_CAP_FWNMI] = SPAPR_CAP_ON;
+    smc->default_caps.caps[SPAPR_CAP_SECURE_GUEST] = SPAPR_CAP_OFF;
     spapr_caps_add_properties(smc, &error_abort);
     smc->irq = &spapr_irq_dual;
     smc->dr_phb_enabled = true;
diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index 679ae7959f..375b7e0b30 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -524,6 +524,27 @@ static void cap_fwnmi_apply(SpaprMachineState *spapr, 
uint8_t val,
     }
 }

+static void cap_secure_guest_apply(SpaprMachineState *spapr,
+                                   uint8_t val, Error **errp)
+{
+    if (!val) {
+        /* capability disabled by default */
+        return;
+    }
+
+    if (!kvm_enabled()) {
+        error_setg(errp, "No PEF support in tcg, try cap-svm=off");
+        return;
+    }
+
+    if (!kvmppc_has_cap_secure_guest()) {
+        error_setg(errp, "KVM implementation does not support secure guests, "
+                   "try cap-svm=off");
+    } else if (kvmppc_enable_cap_secure_guest() < 0) {
+        error_setg(errp, "Error enabling cap-svm, try cap-svm=off");
+    }
+}
+
 SpaprCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
     [SPAPR_CAP_HTM] = {
         .name = "htm",
@@ -632,6 +653,15 @@ SpaprCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
         .type = "bool",
         .apply = cap_fwnmi_apply,
     },
+    [SPAPR_CAP_SECURE_GUEST] = {
+        .name = "svm",
+        .description = "Allow the guest to become a Secure Guest",
+        .index = SPAPR_CAP_SECURE_GUEST,
+        .get = spapr_cap_get_bool,
+        .set = spapr_cap_set_bool,
+        .type = "bool",
+        .apply = cap_secure_guest_apply,
+    },
 };

 static SpaprCapabilities default_caps_with_cpu(SpaprMachineState *spapr,
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index 42d64a0368..7f5289782d 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -81,8 +81,9 @@ typedef enum {
 #define SPAPR_CAP_CCF_ASSIST            0x09
 /* Implements PAPR FWNMI option */
 #define SPAPR_CAP_FWNMI                 0x0A
+#define SPAPR_CAP_SECURE_GUEST          0x0B
 /* Num Caps */
-#define SPAPR_CAP_NUM                   (SPAPR_CAP_FWNMI + 1)
+#define SPAPR_CAP_NUM                   (SPAPR_CAP_SECURE_GUEST + 1)

 /*
  * Capability Values
diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 597f72be1b..9254749cd7 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -88,6 +88,7 @@ static int cap_ppc_safe_indirect_branch;
 static int cap_ppc_count_cache_flush_assist;
 static int cap_ppc_nested_kvm_hv;
 static int cap_large_decr;
+static int cap_ppc_secure_guest;

 static uint32_t debug_inst_opcode;

@@ -135,6 +136,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
     cap_resize_hpt = kvm_vm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT);
     kvmppc_get_cpu_characteristics(s);
     cap_ppc_nested_kvm_hv = kvm_vm_check_extension(s, KVM_CAP_PPC_NESTED_HV);
+    cap_ppc_secure_guest = kvm_vm_check_extension(s, KVM_CAP_PPC_SECURE_GUEST);
     cap_large_decr = kvmppc_get_dec_bits();
     /*
      * Note: setting it to false because there is not such capability
@@ -2532,6 +2534,16 @@ int kvmppc_enable_cap_large_decr(PowerPCCPU *cpu, int 
enable)
     return 0;
 }

+bool kvmppc_has_cap_secure_guest(void)
+{
+    return !!cap_ppc_secure_guest;
+}
+
+int kvmppc_enable_cap_secure_guest(void)
+{
+    return kvm_vm_enable_cap(kvm_state, KVM_CAP_PPC_SECURE_GUEST, 0, 1);
+}
+
 PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void)
 {
     uint32_t host_pvr = mfpvr();
diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
index 332fa0aa1c..a9a3aa67c6 100644
--- a/target/ppc/kvm_ppc.h
+++ b/target/ppc/kvm_ppc.h
@@ -72,6 +72,8 @@ int kvmppc_set_cap_nested_kvm_hv(int enable);
 int kvmppc_get_cap_large_decr(void);
 int kvmppc_enable_cap_large_decr(PowerPCCPU *cpu, int enable);
 int kvmppc_enable_hwrng(void);
+bool kvmppc_has_cap_secure_guest(void);
+int kvmppc_enable_cap_secure_guest(void);
 int kvmppc_put_books_sregs(PowerPCCPU *cpu);
 PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void);
 void kvmppc_check_papr_resize_hpt(Error **errp);
@@ -380,6 +382,16 @@ static inline int kvmppc_enable_cap_large_decr(PowerPCCPU 
*cpu, int enable)
     return -1;
 }

+static inline bool kvmppc_has_cap_secure_guest(void)
+{
+    return false;
+}
+
+static inline int kvmppc_enable_cap_secure_guest(void)
+{
+    return -1;
+}
+
 static inline int kvmppc_enable_hwrng(void)
 {
     return -1;
--
2.23.0