linux-kernel - [PATCH] iommu/s390: Fix memory corruption when using identity domain

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Message-ID: <20250827210828.274527-1-mjrosato@linux.ibm.com>
Date: Wed, 27 Aug 2025 17:08:27 -0400
From: Matthew Rosato <mjrosato@...ux.ibm.com>
To: joro@...tes.org, schnelle@...ux.ibm.com
Cc: will@...nel.org, robin.murphy@....com, gerald.schaefer@...ux.ibm.com,
        jgg@...pe.ca, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, stable@...r.kernel.org,
        Cam Miller <cam@...ux.ibm.com>
Subject: [PATCH] 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@...r.kernel.org
Fixes: 64af12c6ec3a ("iommu/s390: implement iommu passthrough via identity domain")
Reported-by: Cam Miller <cam@...ux.ibm.com>
Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
---
 drivers/iommu/s390-iommu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
index 9c80d61deb2c..d7370347c910 100644
--- a/drivers/iommu/s390-iommu.c
+++ b/drivers/iommu/s390-iommu.c
@@ -1032,7 +1032,8 @@ 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);
-- 
2.50.1