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

commit a1d032a49522cb5368e5dfb945a85899b4c74f65 upstream.

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: 4be130a08420 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index b6c85b760305d63397f2b2af0f8d92403661554c..871a99dcf93e1117acafd15df3f770f11ae3286c 100644 (file)
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -759,14 +759,18 @@ 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: