[PATCH v3] PCI: Fix crash during pci_dev hot-unplug on pseries KVM guest

[Amit Machhiwal]

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 introduces a new flag OF_CREATE_WITH_CSET
to keep track of device nodes created via `of_pci_make_dev_node()` and
later attempt to destroy only such device nodes which have this flag
set.

[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 at linux.ibm.com>
Signed-off-by: Lizhi Hou <lizhi.hou at amd.com>
Signed-off-by: Amit Machhiwal <amachhiw at linux.ibm.com>
---
Changes since v2:
    * Drop v2 changes and introduce a different approach from Lizhi discussed
      over the v2 of this patch
    * V2: https://lore.kernel.org/all/20240715080726.2496198-1-amachhiw@linux.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/pci/of.c   | 3 ++-
 include/linux/of.h | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index dacea3fc5128..bc455370143e 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -653,7 +653,7 @@ 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 || !of_node_check_flag(np, OF_CREATE_WITH_CSET))
 		return;
 	pdev->dev.of_node = NULL;
 
@@ -712,6 +712,7 @@ void of_pci_make_dev_node(struct pci_dev *pdev)
 	if (ret)
 		goto out_free_node;
 
+	of_node_set_flag(np, OF_CREATE_WITH_CSET);
 	np->data = cset;
 	pdev->dev.of_node = np;
 	kfree(name);
diff --git a/include/linux/of.h b/include/linux/of.h
index 85b60ac9eec5..5faa5a1198c6 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -153,6 +153,7 @@ extern struct device_node *of_stdout;
 #define OF_POPULATED_BUS	4 /* platform bus created for children */
 #define OF_OVERLAY		5 /* allocated for an overlay */
 #define OF_OVERLAY_FREE_CSET	6 /* in overlay cset being freed */
+#define OF_CREATE_WITH_CSET	7 /* Created by of_changeset_create_node */
 
 #define OF_BAD_ADDR	((u64)-1)
 

base-commit: 948752d2e010e11b56a877975e7e9158d6d31823
-- 
2.45.2