iommu/s390: Fix memory corruption when using identity domain

JIRA: https://issues.redhat.com/browse/RHEL-113440

commit b3506e9
Author: Matthew Rosato <mjrosato@linux.ibm.com>
Date:   Wed Aug 27 17:08:27 2025 -0400

    iommu/s390: Fix memory corruption when using identity domain

    zpci_get_iommu_ctrs() returns counter information to be reported as part
    of device statistics; these counters are stored as part of the s390_domain.
    The problem, however, is that the identity domain is not backed by an
    s390_domain and so the conversion via to_s390_domain() yields a bad address
    that is zero'd initially and read on-demand later via a sysfs read.
    These counters aren't necessary for the identity domain; just return NULL
    in this case.

    This issue was discovered via KASAN with reports that look like:
    BUG: KASAN: global-out-of-bounds in zpci_fmb_enable_device
    when using the identity domain for a device on s390.

    Cc: stable@vger.kernel.org
    Fixes: 64af12c ("iommu/s390: implement iommu passthrough via identity domain")
    Reported-by: Cam Miller <cam@linux.ibm.com>
    Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
    Tested-by: Cam Miller <cam@linux.ibm.com>
    Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
    Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
    Link: https://lore.kernel.org/r/20250827210828.274527-1-mjrosato@linux.ibm.com
    Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

Signed-off-by: Thomas Huth <thuth@redhat.com>

Author: huth

drivers/iommu/s390-iommu.c

@@ -1031,7 +1031,8 @@ struct zpci_iommu_ctrs *zpci_get_iommu_ctrs(struct zpci_dev *zdev)
 
 	lockdep_assert_held(&zdev->dom_lock);
 
-	if (zdev->s390_domain->type == IOMMU_DOMAIN_BLOCKED)
+	if (zdev->s390_domain->type == IOMMU_DOMAIN_BLOCKED ||
+	    zdev->s390_domain->type == IOMMU_DOMAIN_IDENTITY)
 		return NULL;
 
 	s390_domain = to_s390_domain(zdev->s390_domain);