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s390/mm: Fix NULL pointer dereference 

The recently added check to figure out if a fault happened on gmap ASCE
dereferences the gmap pointer in lowcore without checking that it is not
NULL. For all non-KVM processes the pointer is NULL, so that some value
from lowcore will be read. With the current layouts of struct gmap and
struct lowcore the read value (aka ASCE) is zero, so that this doesn't lead
to any observable bug; at least currently.

Fix this by adding the missing NULL pointer check.

Fixes: 64c3431808 ("s390/entry: compare gmap asce to determine guest/host fault")
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
This commit is contained in:
Sven Schnelle 2024-04-15 07:52:13 +02:00 committed by Alexander Gordeev
parent 6f76592ef6
commit d111855ab7
1 changed files with 2 additions and 1 deletions
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3
arch/s390/kernel/entry.S
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@ -340,7 +340,8 @@ SYM_CODE_START(pgm_check_handler)
mvc __PT_LAST_BREAK(8,%r11),__LC_PGM_LAST_BREAK
stctg %c1,%c1,__PT_CR1(%r11)
#if IS_ENABLED(CONFIG_KVM)
lg %r12,__LC_GMAP
ltg %r12,__LC_GMAP
jz 5f
clc __GMAP_ASCE(8,%r12), __PT_CR1(%r11)
jne 5f
BPENTER __SF_SIE_FLAGS(%r10),_TIF_ISOLATE_BP_GUEST