[PATCH 1/2] s390/ipl: Fix NULL deref in kdump without re-IPL parm block

Some IPL types, like HMC FTP boot or QEMU direct kernel boot, might
not provide an IPL parameter block. In this case, reipl_type_init()
selects IPL_TYPE_UNKNOWN, and reipl_block_actual remains NULL.

kdump passes the re-IPL parameter block to the dump kernel through
os_info. Before commit 3b9678472bab ("s390/ipl: correct kdump reipl
block checksum calculation"), the os_info entry was added only for
IPL types which initialized reipl_block_actual. That commit moved the
os_info update to machine_crash_shutdown(), making it unconditional. As
a result, set_os_info_reipl_block() dereferences reipl_block_actual for
IPL_TYPE_UNKNOWN. This may happen to work by chance when address zero
contains readable lowcore data and the resulting empty os_info entry is
ignored by the dump kernel.

Skip the os_info update when no re-IPL parameter block is available.
Kdump then collect the dump and reboot without setting re-IPL parameter
block.

Fixes: 3b9678472bab ("s390/ipl: correct kdump reipl block checksum calculation")
Signed-off-by: Vasily Gorbik <[email protected]>
---
 arch/s390/kernel/ipl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/s390/kernel/ipl.c b/arch/s390/kernel/ipl.c
index 3c346b02ceb9..7024fc413715 100644
--- a/arch/s390/kernel/ipl.c
+++ b/arch/s390/kernel/ipl.c
@@ -1157,6 +1157,8 @@ static struct attribute_group reipl_nss_attr_group = {
 
 void set_os_info_reipl_block(void)
 {
+	if (!reipl_block_actual)
+		return;
 	os_info_entry_add_data(OS_INFO_REIPL_BLOCK, reipl_block_actual,
 			       reipl_block_actual->hdr.len);
 }
-- 
2.53.0