Message-ID: <20240715080726.2496198-1-amachhiw@linux.ibm.com>
Date: Mon, 15 Jul 2024 13:37:03 +0530
From: Amit Machhiwal <amachhiw@...ux.ibm.com>
To: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Cc: linuxppc-dev@...ts.ozlabs.org, kvm-ppc@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, Rob Herring <robh@...nel.org>,
        Lizhi Hou <lizhi.hou@....com>, Saravana Kannan <saravanak@...gle.com>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Vaidyanathan Srinivasan <svaidy@...ux.ibm.com>,
        Amit Machhiwal <amachhiw@...ux.ibm.com>,
        Kowshik Jois B S <kowsjois@...ux.ibm.com>,
        Lukas Wunner <lukas@...ner.de>
Subject: [PATCH v2] PCI: Fix crash during pci_dev hot-unplug on pseries KVM guest

With CONFIG_PCI_DYNAMIC_OF_NODES [1], a hot-plug and hot-unplug sequence
of a PCI device attached to a PCI-bridge causes following kernel Oops on
a pseries KVM guest:

 RTAS: event: 2, Type: Hotplug Event (229), Severity: 1
 Kernel attempted to read user page (10ec00000048) - exploit attempt? (uid: 0)
 BUG: Unable to handle kernel data access on read at 0x10ec00000048
 Faulting instruction address: 0xc0000000012d8728
 Oops: Kernel access of bad area, sig: 11 [#1]
 LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
<snip>
 NIP [c0000000012d8728] __of_changeset_entry_invert+0x10/0x1ac
 LR [c0000000012da7f0] __of_changeset_revert_entries+0x98/0x180
 Call Trace:
 [c00000000bcc3970] [c0000000012daa60] of_changeset_revert+0x58/0xd8
 [c00000000bcc39c0] [c000000000d0ed78] of_pci_remove_node+0x74/0xb0
 [c00000000bcc39f0] [c000000000cdcfe0] pci_stop_bus_device+0xf4/0x138
 [c00000000bcc3a30] [c000000000cdd140] pci_stop_and_remove_bus_device_locked+0x34/0x64
 [c00000000bcc3a60] [c000000000cf3780] remove_store+0xf0/0x108
 [c00000000bcc3ab0] [c000000000e89e04] dev_attr_store+0x34/0x78
 [c00000000bcc3ad0] [c0000000007f8dd4] sysfs_kf_write+0x70/0xa4
 [c00000000bcc3af0] [c0000000007f7248] kernfs_fop_write_iter+0x1d0/0x2e0
 [c00000000bcc3b40] [c0000000006c9b08] vfs_write+0x27c/0x558
 [c00000000bcc3bf0] [c0000000006ca168] ksys_write+0x90/0x170
 [c00000000bcc3c40] [c000000000033248] system_call_exception+0xf8/0x290
 [c00000000bcc3e50] [c00000000000d05c] system_call_vectored_common+0x15c/0x2ec
<snip>

A git bisect pointed this regression to be introduced via [1] that added
a mechanism to create device tree nodes for parent PCI bridges when a
PCI device is hot-plugged.

The Oops is caused when `pci_stop_dev()` tries to remove a non-existing
device-tree node associated with the pci_dev that was earlier
hot-plugged and was attached under a pci-bridge. The PCI dev header
`dev->hdr_type` being 0, results a conditional check done with
`pci_is_bridge()` into false. Consequently, a call to
`of_pci_make_dev_node()` to create a device node is never made. When at
a later point in time, in the device node removal path, a memcpy is
attempted in `__of_changeset_entry_invert()`; since the device node was
never created, results in an Oops due to kernel read access to a bad
address.

To fix this issue, the patch updates `of_changeset_create_node()` to
allocate a new node only when the device node doesn't exist and init it
in case it does already. Also, introduce `of_pci_free_node()` to be
called to only revert and destroy the changeset device node that was
created via a call to `of_changeset_create_node()`.

[1] commit 407d1a51921e ("PCI: Create device tree node for bridge")

Fixes: 407d1a51921e ("PCI: Create device tree node for bridge")
Reported-by: Kowshik Jois B S <kowsjois@...ux.ibm.com>
Signed-off-by: Lizhi Hou <lizhi.hou@....com>
Signed-off-by: Amit Machhiwal <amachhiw@...ux.ibm.com>
---
Changes since v1:
    * Included Lizhi's suggested changes on V1
    * Fixed below two warnings from Lizhi's changes and rearranged the cleanup
      part a bit in `of_pci_make_dev_node`
	drivers/pci/of.c:611:6: warning: no previous prototype for ‘of_pci_free_node’ [-Wmissing-prototypes]
	  611 | void of_pci_free_node(struct device_node *np)
	      |      ^~~~~~~~~~~~~~~~               
	drivers/pci/of.c: In function ‘of_pci_make_dev_node’:
	drivers/pci/of.c:696:1: warning: label ‘out_destroy_cset’ defined but not used [-Wunused-label]
	  696 | out_destroy_cset:       
	      | ^~~~~~~~~~~~~~~~  
    * V1: https://lore.kernel.org/all/20240703141634.2974589-1-amachhiw@linux.ibm.com/

 drivers/of/dynamic.c  | 16 ++++++++++++----
 drivers/of/unittest.c |  2 +-
 drivers/pci/bus.c     |  3 +--
 drivers/pci/of.c      | 39 ++++++++++++++++++++++++++-------------
 drivers/pci/pci.h     |  2 ++
 include/linux/of.h    |  1 +
 6 files changed, 43 insertions(+), 20 deletions(-)

diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
index dda6092e6d3a..9bba5e82a384 100644
--- a/drivers/of/dynamic.c
+++ b/drivers/of/dynamic.c
@@ -492,21 +492,29 @@ struct device_node *__of_node_dup(const struct device_node *np,
  * a given changeset.
  *
  * @ocs: Pointer to changeset
+ * @np: Pointer to device node. If null, allocate a new node. If not, init an
+ *	existing one.
  * @parent: Pointer to parent device node
  * @full_name: Node full name
  *
  * Return: Pointer to the created device node or NULL in case of an error.
  */
 struct device_node *of_changeset_create_node(struct of_changeset *ocs,
+					     struct device_node *np,
 					     struct device_node *parent,
 					     const char *full_name)
 {
-	struct device_node *np;
 	int ret;
 
-	np = __of_node_dup(NULL, full_name);
-	if (!np)
-		return NULL;
+	if (!np) {
+		np = __of_node_dup(NULL, full_name);
+		if (!np)
+			return NULL;
+	} else {
+		of_node_set_flag(np, OF_DYNAMIC);
+		of_node_set_flag(np, OF_DETACHED);
+	}
+
 	np->parent = parent;
 
 	ret = of_changeset_attach_node(ocs, np);
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index 445ad13dab98..b1bcc9ed40a6 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -871,7 +871,7 @@ static void __init of_unittest_changeset(void)
 	unittest(!of_changeset_add_property(&chgset, parent, ppadd), "fail add prop prop-add\n");
 	unittest(!of_changeset_update_property(&chgset, parent, ppupdate), "fail update prop\n");
 	unittest(!of_changeset_remove_property(&chgset, parent, ppremove), "fail remove prop\n");
-	n22 = of_changeset_create_node(&chgset, n2, "n22");
+	n22 = of_changeset_create_node(&chgset, NULL,  n2, "n22");
 	unittest(n22, "fail create n22\n");
 	unittest(!of_changeset_add_prop_string(&chgset, n22, "prop-str", "abcd"),
 		 "fail add prop prop-str");
diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 826b5016a101..d7ca20cb146a 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -342,8 +342,7 @@ void pci_bus_add_device(struct pci_dev *dev)
 	 */
 	pcibios_bus_add_device(dev);
 	pci_fixup_device(pci_fixup_final, dev);
-	if (pci_is_bridge(dev))
-		of_pci_make_dev_node(dev);
+	of_pci_make_dev_node(dev);
 	pci_create_sysfs_dev_files(dev);
 	pci_proc_attach_device(dev);
 	pci_bridge_d3_update(dev);
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..883bf15211a5 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -608,18 +608,28 @@ int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge)
 
 #ifdef CONFIG_PCI_DYNAMIC_OF_NODES
 
+void of_pci_free_node(struct device_node *np)
+{
+	struct of_changeset *cset;
+
+	cset = (struct of_changeset *)(np + 1);
+
+	np->data = NULL;
+	of_changeset_revert(cset);
+	of_changeset_destroy(cset);
+	of_node_put(np);
+}
+
 void of_pci_remove_node(struct pci_dev *pdev)
 {
 	struct device_node *np;
 
 	np = pci_device_to_OF_node(pdev);
-	if (!np || !of_node_check_flag(np, OF_DYNAMIC))
+	if (!np || np->data != of_pci_free_node)
 		return;
 	pdev->dev.of_node = NULL;
 
-	of_changeset_revert(np->data);
-	of_changeset_destroy(np->data);
-	of_node_put(np);
+	of_pci_free_node(np);
 }
 
 void of_pci_make_dev_node(struct pci_dev *pdev)
@@ -655,14 +665,18 @@ void of_pci_make_dev_node(struct pci_dev *pdev)
 	if (!name)
 		return;
 
-	cset = kmalloc(sizeof(*cset), GFP_KERNEL);
-	if (!cset)
+	np = kzalloc(sizeof(*np) + sizeof(*cset), GFP_KERNEL);
+	if (!np)
 		goto out_free_name;
+	np->full_name = name;
+	of_node_init(np);
+
+	cset = (struct of_changeset *)(np + 1);
 	of_changeset_init(cset);
 
-	np = of_changeset_create_node(cset, ppnode, name);
+	np = of_changeset_create_node(cset, np, ppnode, NULL);
 	if (!np)
-		goto out_destroy_cset;
+		goto out_free_node;
 
 	ret = of_pci_add_properties(pdev, cset, np);
 	if (ret)
@@ -670,19 +684,18 @@ void of_pci_make_dev_node(struct pci_dev *pdev)
 
 	ret = of_changeset_apply(cset);
 	if (ret)
-		goto out_free_node;
+		goto out_destroy_cset;
 
-	np->data = cset;
+	np->data = of_pci_free_node;
 	pdev->dev.of_node = np;
-	kfree(name);
 
 	return;
 
-out_free_node:
-	of_node_put(np);
 out_destroy_cset:
 	of_changeset_destroy(cset);
 	kfree(cset);
+out_free_node:
+	of_node_put(np);
 out_free_name:
 	kfree(name);
 }
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index fd44565c4756..7b1a455306b8 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -702,11 +702,13 @@ struct of_changeset;
 
 #ifdef CONFIG_PCI_DYNAMIC_OF_NODES
 void of_pci_make_dev_node(struct pci_dev *pdev);
+void of_pci_free_node(struct device_node *np);
 void of_pci_remove_node(struct pci_dev *pdev);
 int of_pci_add_properties(struct pci_dev *pdev, struct of_changeset *ocs,
 			  struct device_node *np);
 #else
 static inline void of_pci_make_dev_node(struct pci_dev *pdev) { }
+static inline void of_pci_free_node(struct device_node *np) { }
 static inline void of_pci_remove_node(struct pci_dev *pdev) { }
 #endif
 
diff --git a/include/linux/of.h b/include/linux/of.h
index a0bedd038a05..f774459d0d84 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -1631,6 +1631,7 @@ static inline int of_changeset_update_property(struct of_changeset *ocs,
 }
 
 struct device_node *of_changeset_create_node(struct of_changeset *ocs,
+					     struct device_node *np,
 					     struct device_node *parent,
 					     const char *full_name);
 int of_changeset_add_prop_string(struct of_changeset *ocs,

base-commit: 43db1e03c086ed20cc75808d3f45e780ec4ca26e
-- 
2.45.2

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