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Re: [PATCH v2] target/s390x: support PRNO_TRNG instruction

From: Harald Freudenberger
Subject: Re: [PATCH v2] target/s390x: support PRNO_TRNG instruction
Date: Tue, 02 Aug 2022 13:54:31 +0200
User-agent: Roundcube Webmail/1.4.13 
On 2022-07-19 13:43, Jason A. Donenfeld wrote:

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-rc6.

Cc: Thomas Huth <thuth@redhat.com>
Cc: David Hildenbrand <david@redhat.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/cpu_models.c        |  2 --
 target/s390x/gen-features.c      |  2 ++
 target/s390x/tcg/crypto_helper.c | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/target/s390x/cpu_models.c b/target/s390x/cpu_models.c
index 1a562d2801..90aac3d795 100644
--- a/target/s390x/cpu_models.c
+++ b/target/s390x/cpu_models.c
@@ -421,8 +421,6 @@ static void check_consistency(const S390CPUModel *model) 
         { S390_FEAT_DFP_FAST, S390_FEAT_DFP },
         { S390_FEAT_TRANSACTIONAL_EXE, S390_FEAT_STFLE_49 },
         { S390_FEAT_EDAT_2, S390_FEAT_EDAT},
-        { S390_FEAT_MSA_EXT_5, S390_FEAT_KIMD_SHA_512 },
-        { S390_FEAT_MSA_EXT_5, S390_FEAT_KLMD_SHA_512 },
         { S390_FEAT_MSA_EXT_4, S390_FEAT_MSA_EXT_3 },
         { S390_FEAT_SIE_CMMA, S390_FEAT_CMM },
         { S390_FEAT_SIE_CMMA, S390_FEAT_SIE_GSLS },
diff --git a/target/s390x/gen-features.c b/target/s390x/gen-features.c
index ad140184b9..3d333e2789 100644
--- a/target/s390x/gen-features.c
+++ b/target/s390x/gen-features.c
@@ -749,6 +749,8 @@ static uint16_t qemu_V7_0[] = {
  */
 static uint16_t qemu_MAX[] = {
     S390_FEAT_VECTOR_ENH2,
+    S390_FEAT_MSA_EXT_5,
+    S390_FEAT_PRNO_TRNG,
 };

 /****** END FEATURE DEFS ******/
diff --git a/target/s390x/tcg/crypto_helper.c b/target/s390x/tcg/crypto_helper.c 
index 138d9e7ad9..dccce7f707 100644
--- a/target/s390x/tcg/crypto_helper.c
+++ b/target/s390x/tcg/crypto_helper.c
@@ -12,12 +12,30 @@

 #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"
 #include "exec/exec-all.h"
 #include "exec/cpu_ldst.h"

+static void fill_buf_random(CPUS390XState *env, uintptr_t ra,
+                            uint64_t buf, uint64_t len)
+{
+        uint8_t tmp[256];
+
+        if (!(env->psw.mask & PSW_MASK_64))
+                len = (uint32_t)len;
+
+        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++), tmp[i], ra);
+                len -= block;
+        }
+}
+
uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, uint32_t r2, uint32_t r3, 
                      uint32_t type)
 {
@@ -52,6 +70,20 @@ uint32_t HELPER(msa)(CPUS390XState *env, uint32_t
r1, uint32_t r2, uint32_t r3,
             cpu_stb_data_ra(env, param_addr, subfunc[i], ra);
         }
         break;
+    case 114:
+        if (r1 & 1 || !r1 || r2 & 1 || !r2) {
+ tcg_s390_program_interrupt(env, PGM_SPECIFICATION, ra); 
+                break;
+        }
+
+        fill_buf_random(env, ra, env->regs[r1], env->regs[r1 + 1]);
+        fill_buf_random(env, ra, env->regs[r2], env->regs[r2 + 1]);
+
+        env->regs[r1] += env->regs[r1 + 1];
+        env->regs[r1 + 1] = 0;
+        env->regs[r2] += env->regs[r2 + 1];
+        env->regs[r2 + 1] = 0;
+        break;
     default:
         /* we don't implement any other subfunction yet */
         g_assert_not_reached();
I am absolutely no expert in this qemu code - in fact seen in just now but my feeling is that there should be some more than just handling then 114 subfunction. 
For example something like this:
diff --git a/target/s390x/tcg/crypto_helper.c b/target/s390x/tcg/crypto_helper.c 
index 138d9e7ad9..a0163675b2 100644
--- a/target/s390x/tcg/crypto_helper.c
+++ b/target/s390x/tcg/crypto_helper.c
@@ -12,12 +12,30 @@

 #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"
 #include "exec/exec-all.h"
 #include "exec/cpu_ldst.h"

+static void fill_buf_random(CPUS390XState *env, uintptr_t ra,
+                            uint64_t buf, uint64_t len)
+{
+        uint8_t tmp[256];
+
+        if (!(env->psw.mask & PSW_MASK_64))
+                len = (uint32_t)len;
+
+        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++), tmp[i], ra); 
+                len -= block;
+        }
+}
+
uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, uint32_t r2, uint32_t r3, 
                      uint32_t type)
 {
@@ -45,16 +63,39 @@ uint32_t HELPER(msa)(CPUS390XState *env, uint32_t r1, uint32_t r2, uint32_t r3, 
         tcg_s390_program_interrupt(env, PGM_SPECIFICATION, ra);
     }

-    switch (fc) {
-    case 0: /* query subfunction */
+    /* handle query subfunction */
+    if (fc == 0) {
         for (i = 0; i < 16; i++) {
             param_addr = wrap_address(env, env->regs[1] + i);
             cpu_stb_data_ra(env, param_addr, subfunc[i], ra);
         }
+        return 0;
+    }
+
+    switch (type) {
+    case S390_FEAT_PRNO_TRNG:
+        switch (fc) {
+        case 114: /* CPACF_PRNO_TRNG */
+            if (r1 & 1 || !r1 || r2 & 1 || !r2) {
+                tcg_s390_program_interrupt(env, PGM_SPECIFICATION, ra);
+                break;
+            }
+            fill_buf_random(env, ra, env->regs[r1], env->regs[r1 + 1]);
+            fill_buf_random(env, ra, env->regs[r2], env->regs[r2 + 1]);
+            env->regs[r1] += env->regs[r1 + 1];
+            env->regs[r1 + 1] = 0;
+            env->regs[r2] += env->regs[r2 + 1];
+            env->regs[r2 + 1] = 0;
+            break;
+        default:
+            /* we don't implement any other subfunctions yet */
+            g_assert_not_reached();
+        }
         break;
     default:
-        /* we don't implement any other subfunction yet */
-        g_assert_not_reached();
+            /* we don't implement any other functions yet */
+            g_assert_not_reached();
+        }
     }

     return 0;
And ... it is valid to have each of the two buffer pointers NULL. Not sure 
how this env->regs[x] thing here handles this.
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