[PATCH v2 3/8] s390/sclp: rework sclp boundary and length checks

[Collin Walling <walling@linux.ibm.com>]

Rework the SCLP boundary check to account for different SCLP commands
(eventually) allowing different boundary sizes.

Move the length check code into a separate function, and introduce a
new function to determine the length of the read SCP data (i.e. the size
from the start of the struct to where the CPU entries should begin).

Signed-off-by: Collin Walling <walling@linux.ibm.com>
---
 hw/s390x/sclp.c | 57 ++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 49 insertions(+), 8 deletions(-)

diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
index 2bd618515e..987699e3c4 100644
--- a/hw/s390x/sclp.c
+++ b/hw/s390x/sclp.c
@@ -49,6 +49,34 @@ static inline bool sclp_command_code_valid(uint32_t code)
     return false;
 }
 
+static bool sccb_has_valid_boundary(uint64_t sccb_addr, uint32_t code,
+                                    SCCBHeader *header)
+{
+    uint64_t current_len = sccb_addr + be16_to_cpu(header->length);
+    uint64_t allowed_len = (sccb_addr & PAGE_MASK) + PAGE_SIZE;
+
+    switch (code & SCLP_CMD_CODE_MASK) {
+    default:
+        if (current_len <= allowed_len) {
+            return true;
+        }
+    }
+    header->response_code = cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
+    return false;
+}
+
+/* Calculates sufficient SCCB length to store a full Read SCP/CPU response */
+static bool sccb_has_sufficient_len(SCCB *sccb, int num_cpus, int data_len)
+{
+    int required_len = data_len + num_cpus * sizeof(CPUEntry);
+
+    if (be16_to_cpu(sccb->h.length) < required_len) {
+        sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
+        return false;
+    }
+    return true;
+}
+
 static void prepare_cpu_entries(MachineState *ms, CPUEntry *entry, int *count)
 {
     uint8_t features[SCCB_CPU_FEATURE_LEN] = { 0 };
@@ -66,6 +94,16 @@ static void prepare_cpu_entries(MachineState *ms, CPUEntry *entry, int *count)
     }
 }
 
+/*
+ * The data length denotes the start of the struct to where the first
+ * CPU entry is to be allocated. This value also denotes the offset_cpu
+ * field.
+ */
+static int get_read_scp_info_data_len(void)
+{
+    return offsetof(ReadInfo, entries);
+}
+
 /* Provide information about the configuration, CPUs and storage */
 static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
 {
@@ -74,16 +112,16 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
     int cpu_count;
     int rnsize, rnmax;
     IplParameterBlock *ipib = s390_ipl_get_iplb();
+    int data_len = get_read_scp_info_data_len();
 
-    if (be16_to_cpu(sccb->h.length) < (sizeof(ReadInfo) + cpu_count * sizeof(CPUEntry))) {
-        sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
+    if (!sccb_has_sufficient_len(sccb, machine->possible_cpus->len, data_len)) {
         return;
     }
 
     /* CPU information */
     prepare_cpu_entries(machine, read_info->entries, &cpu_count);
     read_info->entries_cpu = cpu_to_be16(cpu_count);
-    read_info->offset_cpu = cpu_to_be16(offsetof(ReadInfo, entries));
+    read_info->offset_cpu = cpu_to_be16(data_len);
     read_info->highest_cpu = cpu_to_be16(machine->smp.max_cpus - 1);
 
     read_info->ibc_val = cpu_to_be32(s390_get_ibc_val());
@@ -132,16 +170,16 @@ static void sclp_read_cpu_info(SCLPDevice *sclp, SCCB *sccb)
 {
     MachineState *machine = MACHINE(qdev_get_machine());
     ReadCpuInfo *cpu_info = (ReadCpuInfo *) sccb;
+    int data_len = offsetof(ReadCpuInfo, entries);
     int cpu_count;
 
-    if (be16_to_cpu(sccb->h.length) < (sizeof(ReadCpuInfo) + cpu_count * sizeof(CPUEntry))) {
-        sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH);
+    if (!sccb_has_sufficient_len(sccb, machine->possible_cpus->len, data_len)) {
         return;
     }
 
     prepare_cpu_entries(machine, cpu_info->entries, &cpu_count);
     cpu_info->nr_configured = cpu_to_be16(cpu_count);
-    cpu_info->offset_configured = cpu_to_be16(offsetof(ReadCpuInfo, entries));
+    cpu_info->offset_configured = cpu_to_be16(data_len);
     cpu_info->nr_standby = cpu_to_be16(0);
 
     /* The standby offset is 16-byte for each CPU */
@@ -227,6 +265,10 @@ int sclp_service_call_protected(CPUS390XState *env, uint64_t sccb,
         goto out_write;
     }
 
+    if (!sccb_has_valid_boundary(sccb, code, &work_sccb.h)) {
+        goto out_write;
+    }
+
     sclp_c->execute(sclp, &work_sccb, code);
 out_write:
     s390_cpu_pv_mem_write(env_archcpu(env), 0, &work_sccb,
@@ -272,8 +314,7 @@ int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code)
         goto out_write;
     }
 
-    if ((sccb + be16_to_cpu(work_sccb.h.length)) > ((sccb & PAGE_MASK) + PAGE_SIZE)) {
-        work_sccb.h.response_code = cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
+    if (!sccb_has_valid_boundary(sccb, code, &work_sccb.h)) {
         goto out_write;
     }
 
-- 
2.21.3