[PATCH v7 2/2] target/s390x: support PRNO_TRNG instruction

[Jason A. Donenfeld]

In order for hosts running inside of TCG to initialize the kernel's
random number generator, we should support the PRNO_TRNG instruction,
backed in the usual way with the qemu_guest_getrandom helper. This is
confirmed working on Linux 5.19.

Cc: Thomas Huth <thuth@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Cornelia Huck <cohuck@redhat.com>
Cc: Harald Freudenberger <freude@linux.ibm.com>
Cc: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 target/s390x/gen-features.c      |  1 +
 target/s390x/tcg/crypto_helper.c | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/target/s390x/gen-features.c b/target/s390x/gen-features.c
index 85ab69d04e..423ae44315 100644
--- a/target/s390x/gen-features.c
+++ b/target/s390x/gen-features.c
@@ -752,6 +752,7 @@ static uint16_t qemu_MAX[] = {
     S390_FEAT_MSA_EXT_5,
     S390_FEAT_KIMD_SHA_512,
     S390_FEAT_KLMD_SHA_512,
+    S390_FEAT_PRNO_TRNG,
 };
 
 /****** END FEATURE DEFS ******/
diff --git a/target/s390x/tcg/crypto_helper.c b/target/s390x/tcg/crypto_helper.c
index 4d45de8faa..e155ae1f54 100644
--- a/target/s390x/tcg/crypto_helper.c
+++ b/target/s390x/tcg/crypto_helper.c
@@ -14,6 +14,7 @@
 
 #include "qemu/osdep.h"
 #include "qemu/main-loop.h"
+#include "qemu/guest-random.h"
 #include "s390x-internal.h"
 #include "tcg_s390x.h"
 #include "exec/helper-proto.h"
@@ -167,6 +168,31 @@ static int klmd_sha512(CPUS390XState *env, uintptr_t ra, 
uint64_t parameter_bloc
     return 0;
 }
 
+static void fill_buf_random(CPUS390XState *env, uintptr_t ra,
+                            uint64_t *buf_reg, uint64_t *len_reg)
+{
+    uint8_t tmp[256];
+    uint64_t len = *len_reg;
+    int message_reg_len = 64;
+
+    if (!(env->psw.mask & PSW_MASK_64)) {
+        len = (uint32_t)len;
+        message_reg_len = (env->psw.mask & PSW_MASK_32) ? 32 : 24;
+    }
+
+    while (len) {
+        size_t block = MIN(len, sizeof(tmp));
+
+        qemu_guest_getrandom_nofail(tmp, block);
+        for (size_t i = 0; i < block; ++i) {
+            cpu_stb_data_ra(env, wrap_address(env, *buf_reg), tmp[i], ra);
+            *buf_reg = deposit64(*buf_reg, 0, message_reg_len, *buf_reg + 1);
+            --*len_reg;
+        }
+        len -= block;
+    }
+}
+
 uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, uint32_t r2, uint32_t r3,
                      uint32_t type)
 {
@@ -209,6 +235,10 @@ uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, 
uint32_t r2, uint32_t r3,
             return klmd_sha512(env, ra, env->regs[1], &env->regs[r2], 
&env->regs[r2 + 1]);
         }
         break;
+    case 114: /* CPACF_PRNO_TRNG */
+        fill_buf_random(env, ra, &env->regs[r1], &env->regs[r1 + 1]);
+        fill_buf_random(env, ra, &env->regs[r2], &env->regs[r2 + 1]);
+        break;
     default:
         /* we don't implement any other subfunction yet */
         g_assert_not_reached();
-- 
2.35.1