pc-bios: s390x: Save iplb location in lowcore

The POP states that for a list directed IPL the IPLB is stored into
memory by the machine loader and its address is stored at offset 0x14
of the lowcore.

ZIPL currently uses the address in offset 0x14 to access the IPLB and
acquire flags about secure boot. If the IPLB address points into
memory which has an unsupported mix of flags set, ZIPL will panic
instead of booting the OS.

As the lowcore can have quite a high entropy for a guest that did drop
out of protected mode (i.e. rebooted) we encountered the ZIPL panic
quite often.
Signed-off-by: NJanosch Frank <frankja@linux.ibm.com>
Tested-by: NMarc Hartmayer <mhartmay@linux.ibm.com>
Message-Id: <20200304114231.23493-19-frankja@linux.ibm.com>
Reviewed-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>

pc-bios/s390-ccw/jump2ipl.c

@@ -35,6 +35,7 @@ void jump_to_IPL_code(uint64_t address)
 {
     /* store the subsystem information _after_ the bootmap was loaded */
     write_subsystem_identification();
+    write_iplb_location();
 
     /* prevent unknown IPL types in the guest */
     if (iplb.pbt == S390_IPL_TYPE_QEMU_SCSI) {

pc-bios/s390-ccw/main.c

@@ -9,6 +9,7 @@
  */
 
 #include "libc.h"
+#include "helper.h"
 #include "s390-arch.h"
 #include "s390-ccw.h"
 #include "cio.h"
@@ -22,7 +23,7 @@ QemuIplParameters qipl;
 IplParameterBlock iplb __attribute__((__aligned__(PAGE_SIZE)));
 static bool have_iplb;
 static uint16_t cutype;
-LowCore const *lowcore; /* Yes, this *is* a pointer to address 0 */
+LowCore *lowcore; /* Yes, this *is* a pointer to address 0 */
 
 #define LOADPARM_PROMPT "PROMPT  "
 #define LOADPARM_EMPTY  "        "
@@ -42,6 +43,11 @@ void write_subsystem_identification(void)
     *zeroes = 0;
 }
 
+void write_iplb_location(void)
+{
+    lowcore->ptr_iplb = ptr2u32(&iplb);
+}
+
 void panic(const char *string)
 {
     sclp_print(string);

pc-bios/s390-ccw/netmain.c

@@ -40,6 +40,7 @@
 #define DEFAULT_TFTP_RETRIES 20
 
 extern char _start[];
+void write_iplb_location(void) {}
 
 #define KERNEL_ADDR             ((void *)0L)
 #define KERNEL_MAX_SIZE         ((long)_start)

pc-bios/s390-ccw/s390-arch.h

@@ -36,7 +36,13 @@ typedef struct LowCore {
     /* prefix area: defined by architecture */
     PSWLegacy       ipl_psw;                  /* 0x000 */
     uint32_t        ccw1[2];                  /* 0x008 */
-    uint32_t        ccw2[2];                  /* 0x010 */
+    union {
+        uint32_t        ccw2[2];                  /* 0x010 */
+        struct {
+            uint32_t reserved10;
+            uint32_t ptr_iplb;
+        };
+    };
     uint8_t         pad1[0x80 - 0x18];        /* 0x018 */
     uint32_t        ext_params;               /* 0x080 */
     uint16_t        cpu_addr;                 /* 0x084 */
@@ -85,7 +91,7 @@ typedef struct LowCore {
     PSW             io_new_psw;               /* 0x1f0 */
 } __attribute__((packed, aligned(8192))) LowCore;
 
-extern LowCore const *lowcore;
+extern LowCore *lowcore;
 
 static inline void set_prefix(uint32_t address)
 {

pc-bios/s390-ccw/s390-ccw.h

@@ -57,6 +57,7 @@ void consume_io_int(void);
 /* main.c */
 void panic(const char *string);
 void write_subsystem_identification(void);
+void write_iplb_location(void);
 extern char stack[PAGE_SIZE * 8] __attribute__((__aligned__(PAGE_SIZE)));
 unsigned int get_loadparm_index(void);