diff mbox series

[SRU,J,1/1] s390/ism: fix concurrency management in ism_cmd()

Message ID kybele.cve-2025-39726.v1.3cd24883378e4cc0b6bc3a4b4d433dcd.series.J.patch-0001.54d97ded5141.37e4f5278c28d178@canonical.com
State New
Headers show
Series CVE-2025-39726 | expand

Commit Message

Cengiz Can Sept. 18, 2026, 10:53 p.m. UTC 
From: Halil Pasic <pasic@linux.ibm.com>

The s390x ISM device data sheet clearly states that only one
request-response sequence is allowable per ISM function at any point in
time.  Unfortunately as of today the s390/ism driver in Linux does not
honor that requirement. This patch aims to rectify that.

This problem was discovered based on Aliaksei's bug report which states
that for certain workloads the ISM functions end up entering error state
(with PEC 2 as seen from the logs) after a while and as a consequence
connections handled by the respective function break, and for future
connection requests the ISM device is not considered -- given it is in a
dysfunctional state. During further debugging PEC 3A was observed as
well.

A kernel message like
[ 1211.244319] zpci: 061a:00:00.0: Event 0x2 reports an error for PCI function 0x61a
is a reliable indicator of the stated function entering error state
with PEC 2. Let me also point out that a kernel message like
[ 1211.244325] zpci: 061a:00:00.0: The ism driver bound to the device does not support error recovery
is a reliable indicator that the ISM function won't be auto-recovered
because the ISM driver currently lacks support for it.

On a technical level, without this synchronization, commands (inputs to
the FW) may be partially or fully overwritten (corrupted) by another CPU
trying to issue commands on the same function. There is hard evidence that
this can lead to DMB token values being used as DMB IOVAs, leading to
PEC 2 PCI events indicating invalid DMA. But this is only one of the
failure modes imaginable. In theory even completely losing one command
and executing another one twice and then trying to interpret the outputs
as if the command we intended to execute was actually executed and not
the other one is also possible.  Frankly, I don't feel confident about
providing an exhaustive list of possible consequences.

Fixes: 684b89bc39ce ("s390/ism: add device driver for internal shared memory")
Reported-by: Aliaksei Makarau <Aliaksei.Makarau@ibm.com>
Tested-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Tested-by: Aliaksei Makarau <Aliaksei.Makarau@ibm.com>
Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250722161817.1298473-1-wintera@linux.ibm.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
(backported from commit 897e8601b9cff1d054cdd53047f568b0e1995726)
[bot_kybele: include/linux/ism.h does not exist in this tree; struct ism_dev
 lives in drivers/s390/net/ism.h, so cmd_lock was added there and the am-created
 include/linux/ism.h was removed.]
CVE-2025-39726
Assisted-by: kybele:claude-opus-4.8
Signed-off-by: Cengiz Can <cengiz.can@canonical.com>
---
 drivers/s390/net/ism.h     | 1 +
 drivers/s390/net/ism_drv.c | 3 +++
 2 files changed, 4 insertions(+)
diff mbox series

Patch

diff --git a/drivers/s390/net/ism.h b/drivers/s390/net/ism.h
index 38fe90c2597d..4b54bb0c185d 100644
--- a/drivers/s390/net/ism.h
+++ b/drivers/s390/net/ism.h
@@ -191,6 +191,7 @@  struct ism_sba {
 
 struct ism_dev {
 	spinlock_t lock;
+	spinlock_t cmd_lock; /* serializes cmds */
 	struct pci_dev *pdev;
 	struct smcd_dev *smcd;
 
diff --git a/drivers/s390/net/ism_drv.c b/drivers/s390/net/ism_drv.c
index 26cc943d2034..414e4391c82d 100644
--- a/drivers/s390/net/ism_drv.c
+++ b/drivers/s390/net/ism_drv.c
@@ -40,6 +40,7 @@  static int ism_cmd(struct ism_dev *ism, void *cmd)
 	struct ism_req_hdr *req = cmd;
 	struct ism_resp_hdr *resp = cmd;
 
+	spin_lock(&ism->cmd_lock);
 	__ism_write_cmd(ism, req + 1, sizeof(*req), req->len - sizeof(*req));
 	__ism_write_cmd(ism, req, 0, sizeof(*req));
 
@@ -53,6 +54,7 @@  static int ism_cmd(struct ism_dev *ism, void *cmd)
 	}
 	__ism_read_cmd(ism, resp + 1, sizeof(*resp), resp->len - sizeof(*resp));
 out:
+	spin_unlock(&ism->cmd_lock);
 	return resp->ret;
 }
 
@@ -544,6 +546,7 @@  static int ism_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 		return -ENOMEM;
 
 	spin_lock_init(&ism->lock);
+	spin_lock_init(&ism->cmd_lock);
 	dev_set_drvdata(&pdev->dev, ism);
 	ism->pdev = pdev;