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

[Lizhi Hou <lizhi.hou@amd.com>]

On 7/5/24 12:20, Bjorn Helgaas wrote:
> [+cc Lukas, FYI]
>
> On Wed, Jul 03, 2024 at 07:46:34PM +0530, Amit Machhiwal wrote:
>> 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 `pci_stop_dev()` to ensure that a
>> call to `of_pci_remove_node()` is only made for pci-bridge devices.
>>
>> [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@linux.ibm.com>
>> Tested-by: Kowshik Jois B S <kowsjois@linux.ibm.com>
>> Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
> Thanks for the patch and testing!  Would like a reviewed-by from
> Lizhi.

of_pci_make_dev_node() will create of nodes for some endpoint devices 
(not a bridge) as well. And actually this is the main purpose.

Maybe the patch as below would resolve the Oops?

diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
index dda6092e6d3a..3c693b091ecf 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 it is not null, init it directly 
instead of
+ *      allocate a new node.
   * @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..087de26852cc 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/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..92c079b2e570 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)
@@ -672,9 +686,8 @@ void of_pci_make_dev_node(struct pci_dev *pdev)
         if (ret)
                 goto out_free_node;

-       np->data = cset;
+       np->data = of_pci_free_node;
         pdev->dev.of_node = np;
-       kfree(name);

         return;

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,

Thanks,

Lizhi

>
>> ---
>>   drivers/pci/remove.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
>> index d749ea8250d6..4e51c64af416 100644
>> --- a/drivers/pci/remove.c
>> +++ b/drivers/pci/remove.c
>> @@ -22,7 +22,8 @@ static void pci_stop_dev(struct pci_dev *dev)
>>   		device_release_driver(&dev->dev);
>>   		pci_proc_detach_device(dev);
>>   		pci_remove_sysfs_dev_files(dev);
>> -		of_pci_remove_node(dev);
>> +		if (pci_is_bridge(dev))
>> +			of_pci_remove_node(dev);
> IIUC, this basically undoes the work that was done by
> of_pci_make_dev_node().
>
> The call of of_pci_make_dev_node() from pci_bus_add_device() was added
> by 407d1a51921e and is conditional on pci_is_bridge(), so it makes
> sense to me that the remove needs a similar condition.
>
>>   		pci_dev_assign_added(dev, false);
>>   	}
>>
>> base-commit: e9d22f7a6655941fc8b2b942ed354ec780936b3e
>> -- 
>> 2.45.2
>>