[SRU][J][PATCH 1/1] KVM: s390: vsie: fix race during shadow creation

[Ian Whitfield]

From: Christian Borntraeger <borntraeger at linux.ibm.com>

Right now it is possible to see gmap->private being zero in
kvm_s390_vsie_gmap_notifier resulting in a crash.  This is due to the
fact that we add gmap->private == kvm after creation:

static int acquire_gmap_shadow(struct kvm_vcpu *vcpu,
                               struct vsie_page *vsie_page)
{
[...]
        gmap = gmap_shadow(vcpu->arch.gmap, asce, edat);
        if (IS_ERR(gmap))
                return PTR_ERR(gmap);
        gmap->private = vcpu->kvm;

Let children inherit the private field of the parent.

Reported-by: Marc Hartmayer <mhartmay at linux.ibm.com>
Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization")
Cc: <stable at vger.kernel.org>
Cc: David Hildenbrand <david at redhat.com>
Reviewed-by: Janosch Frank <frankja at linux.ibm.com>
Reviewed-by: David Hildenbrand <david at redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda at linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger at linux.ibm.com>
Link: https://lore.kernel.org/r/20231220125317.4258-1-borntraeger@linux.ibm.com
(backported from commit fe752331d4b361d43cfd0b89534b4b2176057c32)
[ijwhitfield: adjusted context due to missing commit
c3235e2dd695 ("KVM: s390: add stat counter for shadow gmap events")]
CVE-2023-52639
Signed-off-by: Ian Whitfield <ian.whitfield at canonical.com>
---
 arch/s390/kvm/vsie.c | 1 -
 arch/s390/mm/gmap.c  | 1 +
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index e07bc0d3df6f..2a53d0e3d34e 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -1206,7 +1206,6 @@ static int acquire_gmap_shadow(struct kvm_vcpu *vcpu,
 	gmap = gmap_shadow(vcpu->arch.gmap, asce, edat);
 	if (IS_ERR(gmap))
 		return PTR_ERR(gmap);
-	gmap->private = vcpu->kvm;
 	WRITE_ONCE(vsie_page->gmap, gmap);
 	return 0;
 }
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 6ea9bfe69bd2..0e662cf12029 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -1675,6 +1675,7 @@ struct gmap *gmap_shadow(struct gmap *parent, unsigned long asce,
 		return ERR_PTR(-ENOMEM);
 	new->mm = parent->mm;
 	new->parent = gmap_get(parent);
+	new->private = parent->private;
 	new->orig_asce = asce;
 	new->edat_level = edat_level;
 	new->initialized = false;
-- 
2.43.0