s390x/ipl: Add type and length checks for IplParameterBlock values

We can check for valid type and lengths of the IplParameterBlock fields
when receiving the struct from the guest.

Length of the IplParameterBlock can be less than 4K. To play safe we can
read and write only required amount of data.
Signed-off-by: NAlexander Yarygin <yarygin@linux.vnet.ibm.com>
Reviewed-by: NDavid Hildenband <dahi@linux.vnet.ibm.com>
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

hw/s390x/ipl.h

@@ -99,6 +99,27 @@ struct S390IPLState {
 };
 typedef struct S390IPLState S390IPLState;
 
+#define S390_IPL_TYPE_FCP 0x00
+#define S390_IPL_TYPE_CCW 0x02
+
 #define S390_IPLB_MIN_CCW_LEN 200
+#define S390_IPLB_MIN_FCP_LEN 384
+
+static inline bool iplb_valid_len(IplParameterBlock *iplb)
+{
+    return be32_to_cpu(iplb->len) <= sizeof(IplParameterBlock);
+}
+
+static inline bool iplb_valid_ccw(IplParameterBlock *iplb)
+{
+    return be32_to_cpu(iplb->len) >= S390_IPLB_MIN_CCW_LEN &&
+           iplb->pbt == S390_IPL_TYPE_CCW;
+}
+
+static inline bool iplb_valid_fcp(IplParameterBlock *iplb)
+{
+    return be32_to_cpu(iplb->len) >= S390_IPLB_MIN_FCP_LEN &&
+           iplb->pbt == S390_IPL_TYPE_FCP;
+}
 
 #endif

target-s390x/misc_helper.c

@@ -233,9 +233,22 @@ void handle_diag_308(CPUS390XState *env, uint64_t r1, uint64_t r3)
             return;
         }
         iplb = g_malloc0(sizeof(IplParameterBlock));
-        cpu_physical_memory_read(addr, iplb, S390_IPLB_MIN_CCW_LEN);
+        cpu_physical_memory_read(addr, iplb, sizeof(iplb->len));
+        if (!iplb_valid_len(iplb)) {
+            env->regs[r1 + 1] = DIAG_308_RC_INVALID;
+            goto out;
+        }
+
+        cpu_physical_memory_read(addr, iplb, be32_to_cpu(iplb->len));
+
+        if (!iplb_valid_ccw(iplb) && !iplb_valid_fcp(iplb)) {
+            env->regs[r1 + 1] = DIAG_308_RC_INVALID;
+            goto out;
+        }
+
         s390_ipl_update_diag308(iplb);
         env->regs[r1 + 1] = DIAG_308_RC_OK;
+out:
         g_free(iplb);
         return;
     case 6:
@@ -250,7 +263,7 @@ void handle_diag_308(CPUS390XState *env, uint64_t r1, uint64_t r3)
         }
         iplb = s390_ipl_get_iplb();
         if (iplb) {
-            cpu_physical_memory_write(addr, iplb, S390_IPLB_MIN_CCW_LEN);
+            cpu_physical_memory_write(addr, iplb, be32_to_cpu(iplb->len));
             env->regs[r1 + 1] = DIAG_308_RC_OK;
         } else {
             env->regs[r1 + 1] = DIAG_308_RC_NO_CONF;