[Qemu-devel] [PATCH v2 2/2] ppc/spapr_hcall: Implement H_RANDOM hypercall in QEMU

[Thomas Huth <thuth@redhat.com>]

The PAPR interface provides a hypercall to pass high-quality
hardware generated random numbers to guests. So let's provide
this call in QEMU, too, so that guests that do not support
virtio-rnd yet can get good random numbers, too.
Please note that this hypercall should provide "good" random data
instead of pseudo-random, so the function uses the RngBackend to
retrieve the values instead of using a "simple" library function
like rand() or g_random_int(). Since there are multiple RngBackends
available, the user must select an appropriate backend via the
"h-random" property of the the machine state to enable it, e.g.

 qemu-system-ppc64 -M pseries,h-random=rng-random ...

to use the /dev/random backend, or "h-random=rng-egd" to use the
Entropy Gathering Daemon instead.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 hw/ppc/spapr.c         | 36 +++++++++++++++++++++---
 hw/ppc/spapr_hcall.c   | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++
 include/hw/ppc/spapr.h |  2 ++
 3 files changed, 109 insertions(+), 4 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index bc3a112..3db87b5 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -312,7 +312,8 @@ static void *spapr_create_fdt_skel(hwaddr initrd_base,
                                    hwaddr kernel_size,
                                    bool little_endian,
                                    const char *kernel_cmdline,
-                                   uint32_t epow_irq)
+                                   uint32_t epow_irq,
+                                   bool enable_h_random)
 {
     void *fdt;
     uint32_t start_prop = cpu_to_be32(initrd_base);
@@ -466,7 +467,7 @@ static void *spapr_create_fdt_skel(hwaddr initrd_base,
 
     _FDT((fdt_end_node(fdt)));
 
-    if (kvmppc_hwrng_present()) {
+    if (enable_h_random) {
         _FDT(fdt_begin_node(fdt, "ibm,platform-facilities"));
 
         _FDT(fdt_property_string(fdt, "name", "ibm,platform-facilities"));
@@ -1472,7 +1473,7 @@ static void ppc_spapr_init(MachineState *machine)
     uint32_t initrd_base = 0;
     long kernel_size = 0, initrd_size = 0;
     long load_limit, fw_size;
-    bool kernel_le = false;
+    bool kernel_le = false, enable_h_random;
     char *filename;
 
     msi_supported = true;
@@ -1699,6 +1700,10 @@ static void ppc_spapr_init(MachineState *machine)
     }
     g_free(filename);
 
+    /* Enable H_RANDOM hypercall if requested by user or supported by kernel */
+    enable_h_random = kvmppc_hwrng_present() ||
+                      !spapr_h_random_init(spapr->h_random_type);
+
     /* FIXME: Should register things through the MachineState's qdev
      * interface, this is a legacy from the sPAPREnvironment structure
      * which predated MachineState but had a similar function */
@@ -1710,7 +1715,8 @@ static void ppc_spapr_init(MachineState *machine)
     spapr->fdt_skel = spapr_create_fdt_skel(initrd_base, initrd_size,
                                             kernel_size, kernel_le,
                                             kernel_cmdline,
-                                            spapr->check_exception_irq);
+                                            spapr->check_exception_irq,
+                                            enable_h_random);
     assert(spapr->fdt_skel != NULL);
 
     /* used by RTAS */
@@ -1810,6 +1816,21 @@ static void spapr_set_kvm_type(Object *obj, const char *value, Error **errp)
     spapr->kvm_type = g_strdup(value);
 }
 
+static char *spapr_get_h_random_type(Object *obj, Error **errp)
+{
+    sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
+
+    return g_strdup(spapr->h_random_type);
+}
+
+static void spapr_set_h_random_type(Object *obj, const char *val, Error **errp)
+{
+    sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
+
+    g_free(spapr->h_random_type);
+    spapr->h_random_type = g_strdup(val);
+}
+
 static void spapr_machine_initfn(Object *obj)
 {
     object_property_add_str(obj, "kvm-type",
@@ -1817,6 +1838,13 @@ static void spapr_machine_initfn(Object *obj)
     object_property_set_description(obj, "kvm-type",
                                     "Specifies the KVM virtualization mode (HV, PR)",
                                     NULL);
+
+    object_property_add_str(obj, "h-random", spapr_get_h_random_type,
+                            spapr_set_h_random_type, NULL);
+    object_property_set_description(obj, "h-random",
+                                    "Select RNG backend for H_RANDOM hypercall "
+                                    "(rng-random, rng-egd)",
+                                    NULL);
 }
 
 static void ppc_cpu_do_nmi_on_cpu(void *arg)
diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index 652ddf6..ff9d4fd 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -1,4 +1,8 @@
 #include "sysemu/sysemu.h"
+#include "sysemu/rng.h"
+#include "sysemu/rng-random.h"
+#include "qom/object_interfaces.h"
+#include "qemu/error-report.h"
 #include "cpu.h"
 #include "helper_regs.h"
 #include "hw/ppc/spapr.h"
@@ -929,6 +933,77 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu_,
     return H_SUCCESS;
 }
 
+typedef struct HRandomData {
+    QemuSemaphore sem;
+    union {
+        uint64_t v64;
+        uint8_t v8[8];
+    } val;
+    int received;
+} HRandomData;
+
+static RndRandom *hrandom_rng;
+
+static void random_recv(void *dest, const void *src, size_t size)
+{
+    HRandomData *hrcrdp = dest;
+
+    if (src && size > 0) {
+        memcpy(&hrcrdp->val.v8[hrcrdp->received], src, size);
+        hrcrdp->received += size;
+    }
+    qemu_sem_post(&hrcrdp->sem);
+}
+
+static target_ulong h_random(PowerPCCPU *cpu, sPAPRMachineState *spapr,
+                             target_ulong opcode, target_ulong *args)
+{
+    HRandomData hrcrd;
+
+    if (!hrandom_rng) {
+        return H_HARDWARE;
+    }
+
+    qemu_sem_init(&hrcrd.sem, 0);
+    hrcrd.val.v64 = 0;
+    hrcrd.received = 0;
+
+    qemu_mutex_unlock_iothread();
+    while (hrcrd.received < 8) {
+        rng_backend_request_entropy((RngBackend *)hrandom_rng,
+                                    8 - hrcrd.received, random_recv, &hrcrd);
+        qemu_sem_wait(&hrcrd.sem);
+    }
+    qemu_mutex_lock_iothread();
+
+    qemu_sem_destroy(&hrcrd.sem);
+    args[0] = hrcrd.val.v64;
+
+    return H_SUCCESS;
+}
+
+int spapr_h_random_init(const char *backend_type)
+{
+    Error *local_err = NULL;
+
+    if (!backend_type) {
+        return -1;
+    }
+
+    hrandom_rng = RNG_RANDOM(object_new(backend_type));
+    user_creatable_complete(OBJECT(hrandom_rng), &local_err);
+    if (local_err) {
+        error_printf("Failed to initialize backend for H_RANDOM:\n  %s\n",
+                     error_get_pretty(local_err));
+        object_unref(OBJECT(hrandom_rng));
+        return -1;
+    }
+
+    spapr_register_hypercall(H_RANDOM, h_random);
+
+    return 0;
+}
+
 static spapr_hcall_fn papr_hypercall_table[(MAX_HCALL_OPCODE / 4) + 1];
 static spapr_hcall_fn kvmppc_hypercall_table[KVMPPC_HCALL_MAX - KVMPPC_HCALL_BASE + 1];
 
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index ab8906f..de17624 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -76,6 +76,7 @@ struct sPAPRMachineState {
 
     /*< public >*/
     char *kvm_type;
+    char *h_random_type;
 };
 
 #define H_SUCCESS         0
@@ -592,6 +593,7 @@ int spapr_tcet_dma_dt(void *fdt, int node_off, const char *propname,
 void spapr_pci_switch_vga(bool big_endian);
 void spapr_hotplug_req_add_event(sPAPRDRConnector *drc);
 void spapr_hotplug_req_remove_event(sPAPRDRConnector *drc);
+int spapr_h_random_init(const char *backend_type);
 
 /* rtas-configure-connector state */
 struct sPAPRConfigureConnectorState {
-- 
1.8.3.1