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

[sashiko-bot@kernel.org]

> Unlike kdump, which passes the re-IPL parameter block through os_info,
> the stand-alone dump passes it through the IPL parm block address and
> checksum in lowcore.
> 
> 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. Nevertheless,
> dump_reipl_run() unconditionally dereferences it when preparing the
> lowcore fields. This may happen to work by chance when address zero
> contains readable lowcore data. A zero IPL parameter block address is
> then stored in lowcore, causing the stand-alone dumper to enter disabled
> wait after completing the dump.
> 
> Explicitly store a zero IPL parameter block address and checksum when no
> re-IPL parameter block is available. This does not change the behavior:
> the stand-alone dumper completes the dump and halts, while valid re-IPL
> parameter blocks continue to be handled as before.
> 
> Fixes: 099b76513992 ("[S390] Automatic IPL after dump")
> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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