scalar-crypto: v0.9.4/arch-review entropy source updates.

- Post arch review updates to the entropy source:

- New address is 0x546

- Removed old references to mentropy and mnoise.

- Throw invalid opcode exception when reading without writing.

- Missing: mseccfg register with SKES bit. Waiting for rest of
  register to be implemented.

 On branch master
 Your branch is up-to-date with 'origin/master'.

 Changes to be committed:
	modified:   riscv/encoding.h
	modified:   riscv/entropy_source.h
	modified:   riscv/processor.cc

riscv/encoding.h

@@ -1035,10 +1035,6 @@
 #define MASK_FCVT_H_L  0xfff0007f
 #define MATCH_FCVT_H_LU 0xd4300053
 #define MASK_FCVT_H_LU  0xfff0007f
-#define MATCH_POLLENTROPY 0xf1500073
-#define MASK_POLLENTROPY  0xfffff07f
-#define MATCH_GETNOISE 0x7a900073
-#define MASK_GETNOISE  0xfffff07f
 #define MATCH_SM4ED 0x30000033
 #define MASK_SM4ED  0x3e00707f
 #define MATCH_SM4KS 0x34000033
@@ -3013,8 +3009,7 @@
 #define CSR_MARCHID 0xf12
 #define CSR_MIMPID 0xf13
 #define CSR_MHARTID 0xf14
-#define CSR_MENTROPY 0xf15
-#define CSR_MNOISE 0x7a9
+#define CSR_SENTROPY 0x546
 #define CSR_HTIMEDELTAH 0x615
 #define CSR_CYCLEH 0xc80
 #define CSR_TIMEH 0xc81
@@ -3477,8 +3472,6 @@ DECLARE_INSN(fcvt_l_h, MATCH_FCVT_L_H, MASK_FCVT_L_H)
 DECLARE_INSN(fcvt_lu_h, MATCH_FCVT_LU_H, MASK_FCVT_LU_H)
 DECLARE_INSN(fcvt_h_l, MATCH_FCVT_H_L, MASK_FCVT_H_L)
 DECLARE_INSN(fcvt_h_lu, MATCH_FCVT_H_LU, MASK_FCVT_H_LU)
-DECLARE_INSN(pollentropy, MATCH_POLLENTROPY, MASK_POLLENTROPY)
-DECLARE_INSN(getnoise, MATCH_GETNOISE, MASK_GETNOISE)
 DECLARE_INSN(sm4ed, MATCH_SM4ED, MASK_SM4ED)
 DECLARE_INSN(sm4ks, MATCH_SM4KS, MASK_SM4KS)
 DECLARE_INSN(sm3p0, MATCH_SM3P0, MASK_SM3P0)
@@ -4573,8 +4566,7 @@ DECLARE_CSR(mvendorid, CSR_MVENDORID)
 DECLARE_CSR(marchid, CSR_MARCHID)
 DECLARE_CSR(mimpid, CSR_MIMPID)
 DECLARE_CSR(mhartid, CSR_MHARTID)
-DECLARE_CSR(mentropy, CSR_MENTROPY)
-DECLARE_CSR(mnoise, CSR_MNOISE)
+DECLARE_CSR(sentropy, CSR_SENTROPY)
 DECLARE_CSR(htimedeltah, CSR_HTIMEDELTAH)
 DECLARE_CSR(cycleh, CSR_CYCLEH)
 DECLARE_CSR(timeh, CSR_TIMEH)

riscv/entropy_source.h

@@ -11,10 +11,10 @@ class entropy_source {
 
 public:
 
-  // Valid return codes for OPST bits [31:30] when reading mentropy.
+  // Valid return codes for OPST bits [31:30] when reading sentropy.
   static const uint32_t OPST_BIST = 0x0 << 30;
-  static const uint32_t OPST_ES16 = 0x1 << 30;
-  static const uint32_t OPST_WAIT = 0x2 << 30;
+  static const uint32_t OPST_WAIT = 0x1 << 30;
+  static const uint32_t OPST_ES16 = 0x2 << 30;
   static const uint32_t OPST_DEAD = 0x3 << 30;
 
   //
@@ -27,27 +27,28 @@ public:
   }
 
   //
-  // mentropy register
+  // sentropy register
   // ------------------------------------------------------------
 
-  void set_mentropy(reg_t val) {
-    // Always ignore writes to mentropy.
-    // This CSR *must never* accept write values, it is strictly read only.
+  void set_sentropy(reg_t val) {
+    // Always ignore writes to sentropy.
+    // This CSR is strictly read only. It occupies a RW CSR address
+    // to handle the side-effect of the changing seed value on a read.
   }
 
 
   //
-  // The format of mentropy is described in Table 3 / Section 4.1 of
+  // The format of sentropy is described in Section 4.1 of
   // the scalar cryptography specification.
-  reg_t get_mentropy() {
+  reg_t get_sentropy() {
 
     uint32_t result  = 0;
 
-    // Currently, always return ES16 (i.e. good randomness) unless in
-    // noise capture mode.  In the future, we can more realistically model
-    // things like WAIT states, BIST warm up and maybe scriptable entry
-    // into the DEAD state, but until then, this is the bare minimum.
-    uint32_t return_status = noise_capture_mode ? OPST_BIST : OPST_ES16;
+    // Currently, always return ES16 (i.e. good randomness) In the future, we
+    // can more realistically model things like WAIT states, BIST warm up and
+    // maybe scriptable entry into the DEAD state, but until then, this is
+    // the bare minimum.
+    uint32_t return_status = OPST_ES16;
 
     if(return_status == OPST_ES16) {
 
@@ -82,38 +83,10 @@ public:
     return (reg_t)result;
   }
 
-  //
-  // mnoise register
-  // ------------------------------------------------------------
-
-
-  void set_mnoise(reg_t val) {
-      // Almost all of the behaviour for mnoise is vendor specific,
-      // except for bit 31.
-      int new_noisemode = (val >> 31) & 0x1;
-      noise_capture_mode = new_noisemode == 1;
-  }
-
-
-  reg_t get_mnoise() {
-      reg_t to_return = 0;
-
-      if(this -> noise_capture_mode) {
-          // Set bit 31 indicating we are in noise capture mode.
-          to_return |= 0x1 << 31;
-      }
-
-      return to_return;
-  }
-
   //
   // Utility / support variables and functions.
   // ------------------------------------------------------------
 
-  // The ES is in noise capture mode?
-  // If so, then get_mentropy must always return OPST_BIST.
-  bool noise_capture_mode = false;
-
   // The file to read entropy from.
   std::string randomness_source = "/dev/urandom";
 

riscv/processor.cc

@@ -905,11 +905,8 @@ void processor_t::set_csr(int which, reg_t val)
 
   switch (which)
   {
-    case CSR_MENTROPY:
-      es.set_mentropy(val);
-      break;
-    case CSR_MNOISE:
-      es.set_mnoise(val);
+    case CSR_SENTROPY:
+      es.set_sentropy(val);
       break;
     case CSR_FFLAGS:
       dirty_fp_state;
@@ -1396,8 +1393,7 @@ void processor_t::set_csr(int which, reg_t val)
     case CSR_DPC:
     case CSR_DSCRATCH0:
     case CSR_DSCRATCH1:
-    case CSR_MENTROPY:
-    case CSR_MNOISE:
+    case CSR_SENTROPY:
       LOG_CSR(which);
       break;
   }
@@ -1462,14 +1458,13 @@ reg_t processor_t::get_csr(int which, insn_t insn, bool write, bool peek)
 
   switch (which)
   {
-    case CSR_MENTROPY:
-      if(!supports_extension('K'))
-          break;
-      ret(es.get_mentropy());
-    case CSR_MNOISE:
-      if(!supports_extension('K'))
-          break;
-      ret(es.get_mnoise());
+    case CSR_SENTROPY:
+      if (!supports_extension('K'))
+        break;
+      /* Read-only access disallowed due to wipe-on-read side effect */
+      if (!write)
+        break;
+      ret(es.get_sentropy());
     case CSR_FFLAGS:
       require_fp;
       if (!supports_extension('F'))