[PATCH v1 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>
---
 hw/s390x/sclp.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
index 470d5da7a2..748d04a0e2 100644
--- a/hw/s390x/sclp.c
+++ b/hw/s390x/sclp.c
@@ -244,15 +244,16 @@ 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);
         goto out_write;
     }
 
+    s390_cpu_pv_mem_read(env_archcpu(env), 0, &work_sccb, work_sccb.h.length);
+
     if (!check_sccb_boundary_valid(sccb, code, &work_sccb)) {
         goto out_write;
     }
@@ -271,8 +272,6 @@ 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;
@@ -290,13 +289,16 @@ 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)) {
         return -PGM_SPECIFICATION;
     }
 
+    /* the header contains the actual length of the sccb */
+    cpu_physical_memory_read(sccb, &work_sccb, work_sccb.h.length);
+
     if (!sclp_command_code_valid(code)) {
         work_sccb.h.response_code = cpu_to_be16(SCLP_RC_INVALID_SCLP_COMMAND);
         goto out_write;
-- 
2.21.1