riscv: Make sure an exception is raised if a pte is malformed

As per the specification, in 64-bit, if any of the pte reserved bits
60-54 is set an exception should be triggered (see 4.4.1, "Addressing and
Memory Protection"). In addition, we must check the napot/pbmt bits are
not set if those extensions are not active.

Reported-by: Andrea Parri <andrea@rivosinc.com>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230420150220.60919-1-alexghiti@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu_bits.h

@@ -644,6 +644,7 @@ typedef enum {
 #define PTE_SOFT            0x300 /* Reserved for Software */
 #define PTE_PBMT            0x6000000000000000ULL /* Page-based memory types */
 #define PTE_N               0x8000000000000000ULL /* NAPOT translation */
+#define PTE_RESERVED        0x1FC0000000000000ULL /* Reserved bits */
 #define PTE_ATTR            (PTE_N | PTE_PBMT) /* All attributes bits */
 
 /* Page table PPN shift amount */

target/riscv/cpu_helper.c

@@ -927,13 +927,20 @@ restart:
 
         if (riscv_cpu_sxl(env) == MXL_RV32) {
             ppn = pte >> PTE_PPN_SHIFT;
-        } else if (pbmte || riscv_cpu_cfg(env)->ext_svnapot) {
-            ppn = (pte & (target_ulong)PTE_PPN_MASK) >> PTE_PPN_SHIFT;
         } else {
-            ppn = pte >> PTE_PPN_SHIFT;
-            if ((pte & ~(target_ulong)PTE_PPN_MASK) >> PTE_PPN_SHIFT) {
+            if (pte & PTE_RESERVED) {
+                return TRANSLATE_FAIL;
+            }
+
+            if (!pbmte && (pte & PTE_PBMT)) {
                 return TRANSLATE_FAIL;
             }
+
+            if (!riscv_cpu_cfg(env)->ext_svnapot && (pte & PTE_N)) {
+                return TRANSLATE_FAIL;
+            }
+
+            ppn = (pte & (target_ulong)PTE_PPN_MASK) >> PTE_PPN_SHIFT;
         }
 
         if (!(pte & PTE_V)) {