[PATCH v4 4/8] s390/sclp: read sccb from mem based on sccb length

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

The header of the SCCB contains the actual length of the SCCB. Instead
of using a static 4K size, let's allow for a variable size determined
by the value set in the header. The proper checks are already in place
to ensure the SCCB length is sufficent to store a full response, and
that the length does not cross any explicitly-set boundaries.

Signed-off-by: Collin Walling <walling@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
---
 hw/s390x/sclp.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
index 5899c1e3b8..1feba6f692 100644
--- a/hw/s390x/sclp.c
+++ b/hw/s390x/sclp.c
@@ -251,9 +251,8 @@ int sclp_service_call_protected(CPUS390XState *env, uint64_t sccb,
     SCLPDevice *sclp = get_sclp_device();
     SCLPDeviceClass *sclp_c = SCLP_GET_CLASS(sclp);
     SCCB work_sccb;
-    hwaddr sccb_len = sizeof(SCCB);
 
-    s390_cpu_pv_mem_read(env_archcpu(env), 0, &work_sccb, sccb_len);
+    s390_cpu_pv_mem_read(env_archcpu(env), 0, &work_sccb, sizeof(SCCBHeader));
 
     if (!sclp_command_code_valid(code)) {
         work_sccb.h.response_code = cpu_to_be16(SCLP_RC_INVALID_SCLP_COMMAND);
@@ -264,6 +263,9 @@ int sclp_service_call_protected(CPUS390XState *env, uint64_t sccb,
         goto out_write;
     }
 
+    s390_cpu_pv_mem_read(env_archcpu(env), 0, &work_sccb,
+                         be16_to_cpu(work_sccb.h.length));
+
     sclp_c->execute(sclp, &work_sccb, code);
 out_write:
     s390_cpu_pv_mem_write(env_archcpu(env), 0, &work_sccb,
@@ -278,8 +280,6 @@ int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code)
     SCLPDeviceClass *sclp_c = SCLP_GET_CLASS(sclp);
     SCCB work_sccb;
 
-    hwaddr sccb_len = sizeof(SCCB);
-
     /* first some basic checks on program checks */
     if (env->psw.mask & PSW_MASK_PSTATE) {
         return -PGM_PRIVILEGED;
@@ -297,7 +297,7 @@ int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code)
      * from playing dirty tricks by modifying the memory content after
      * the host has checked the values
      */
-    cpu_physical_memory_read(sccb, &work_sccb, sccb_len);
+    cpu_physical_memory_read(sccb, &work_sccb, sizeof(SCCBHeader));
 
     /* Valid sccb sizes */
     if (be16_to_cpu(work_sccb.h.length) < sizeof(SCCBHeader)) {
@@ -313,6 +313,9 @@ int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code)
         goto out_write;
     }
 
+    /* the header contains the actual length of the sccb */
+    cpu_physical_memory_read(sccb, &work_sccb, be16_to_cpu(work_sccb.h.length));
+
     sclp_c->execute(sclp, &work_sccb, code);
 out_write:
     cpu_physical_memory_write(sccb, &work_sccb,
-- 
2.26.2