Commit a1d032a4 authored Apr 03, 2020 by David Hildenbrand Committed by Christian Borntraeger Apr 07, 2020

KVM: s390: vsie: Fix region 1 ASCE sanity shadow address checks



In case we have a region 1 the following calculation
(31 + ((gmap->asce & _ASCE_TYPE_MASK) >> 2)*11)
results in 64. As shifts beyond the size are undefined the compiler is
free to use instructions like sllg. sllg will only use 6 bits of the
shift value (here 64) resulting in no shift at all. That means that ALL
addresses will be rejected.

The can result in endless loops, e.g. when prefix cannot get mapped.

Fixes: 4be130a0 ("s390/mm: add shadow gmap support")
Tested-by: Janosch Frank <frankja@linux.ibm.com>
Reported-by: Janosch Frank <frankja@linux.ibm.com>
Cc: <stable@vger.kernel.org> # v4.8+
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20200403153050.20569-2-david@redhat.com


Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
[borntraeger@de.ibm.com: fix patch description, remove WARN_ON_ONCE]
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

parent 8c1b724d

arch/s390/mm/gmap.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -787,14 +787,18 @@ static void gmap_call_notifier(struct gmap *gmap, unsigned long start,
		static inline unsigned long gmap_table_walk(struct gmap gmap,
		unsigned long gaddr, int level)
		{
		const int asce_type = gmap->asce & _ASCE_TYPE_MASK;
		unsigned long *table;

		if ((gmap->asce & _ASCE_TYPE_MASK) + 4 < (level * 4))
		return NULL;
		if (gmap_is_shadow(gmap) && gmap->removed)
		return NULL;
		if (gaddr & (-1UL << (31 + ((gmap->asce & _ASCE_TYPE_MASK) >> 2)*11)))

		if (asce_type != _ASCE_TYPE_REGION1 &&
		gaddr & (-1UL << (31 + (asce_type >> 2) * 11)))
		return NULL;

		table = gmap->table;
		switch (gmap->asce & _ASCE_TYPE_MASK) {
		case _ASCE_TYPE_REGION1:

Admin message