[PATCH v2] PCI: Fix crash during pci_dev hot-unplug on pseries KVM guest
Lizhi Hou
lizhi.hou at amd.com
Fri Jul 26 09:06:34 AEST 2024
Hi Amit,
I try to follow the option which add a OF flag. If Rob is ok with this,
I would suggest to use it instead of V1 patch
diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
index dda6092e6d3a..a401ed0463d9 100644
--- a/drivers/of/dynamic.c
+++ b/drivers/of/dynamic.c
@@ -382,6 +382,11 @@ void of_node_release(struct kobject *kobj)
__func__, node);
}
+ if (of_node_check_flag(node, OF_CREATED_WITH_CSET)) {
+ of_changeset_revert(node->data);
+ of_changeset_destroy(node->data);
+ }
+
if (node->child)
pr_err("ERROR: %s() unexpected children for %pOF/%s\n",
__func__, node->parent, node->full_name);
@@ -507,6 +512,7 @@ struct device_node *of_changeset_create_node(struct
of_changeset *ocs,
np = __of_node_dup(NULL, full_name);
if (!np)
return NULL;
+ of_node_set_flag(np, OF_CREATED_WITH_CSET);
np->parent = parent;
ret = of_changeset_attach_node(ocs, np);
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index 445ad13dab98..191ab771d9e8 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -895,8 +895,6 @@ static void __init of_unittest_changeset(void)
"'%pOF' not added\n", n22);
of_node_put(np);
- unittest(!of_changeset_revert(&chgset), "revert failed\n");
-
unittest(!of_find_node_by_path("/testcase-data/changeset/n2/n21"),
"'%pOF' still present after revert\n", n21);
@@ -908,8 +906,6 @@ static void __init of_unittest_changeset(void)
if (!ret)
unittest(strcmp(propstr, "hello") == 0, "original value
not in updated property after revert");
- of_changeset_destroy(&chgset);
-
of_node_put(n1);
of_node_put(n2);
of_node_put(n21);
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..836aaba752bb 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -613,12 +613,10 @@ 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_CREATED_WITH_CSET))
return;
pdev->dev.of_node = NULL;
- of_changeset_revert(np->data);
- of_changeset_destroy(np->data);
of_node_put(np);
}
diff --git a/include/linux/of.h b/include/linux/of.h
index a0bedd038a05..a46317f6626e 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_CREATED_WITH_CSET 7 /* created by of_changeset_create_node */
#define OF_BAD_ADDR ((u64)-1)
Thanks,
Lizhi
On 7/25/24 10:45, Amit Machhiwal wrote:
> Hi Lizhi, Rob,
>
> Sorry for responding late. I got busy with some other things.
>
> On 2024/07/23 02:08 PM, Lizhi Hou wrote:
>> On 7/23/24 12:54, Rob Herring wrote:
>>> On Tue, Jul 23, 2024 at 12:21 PM Lizhi Hou <lizhi.hou at amd.com> wrote:
>>>> On 7/23/24 09:21, Rob Herring wrote:
>>>>> On Mon, Jul 15, 2024 at 01:52:30PM -0700, Lizhi Hou wrote:
>>>>>> On 7/15/24 11:55, Rob Herring wrote:
>>>>>>> On Mon, Jul 15, 2024 at 2:08 AM Amit Machhiwal <amachhiw at linux.ibm.com> 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 `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 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 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);
>>>>>>> Are we going to rename the function to
>>>>>>> of_changeset_create_or_maybe_modify_node()? No. The functions here are
>>>>>>> very clear in that they allocate new objects and don't reuse what's
>>>>>>> passed in.
>>>>>> Ok. How about keeping of_changeset_create_node unchanged.
>>>>>>
>>>>>> Instead, call kzalloc(), of_node_init() and of_changeset_attach_node()
>>>>>>
>>>>>> in of_pci_make_dev_node() directly.
>>>>>>
>>>>>> A similar example is dlpar_parse_cc_node().
>>>>>>
>>>>>>
>>>>>> Does this sound better?
>>>>> No, because really that code should be re-written using of_changeset
>>>>> API.
>>>>>
>>>>> My suggestion is add a data pointer to struct of_changeset and then set
>>>>> that to something to know the data ptr is a changeset and is your
>>>>> changeset.
>>>> I do not fully understand the point. I think the issue is that we do not
>>>> know if a given of_node is created by of_pci_make_dev_node(), correct?
>>> Yes.
>>>
>>>> of_node->data can point to anything. And we do not know if it points a
>>>> cset or not.
>>> Right. But instead of checking "of_node->data == of_pci_free_node",
>>> you would just be checking "*(of_node->data) == of_pci_free_node"
>> if of_node->data is a char* pointer, it would be panic. So I used
>> of_node->data == of_pci_free_node.
>>
>>> (omitting a NULL check and cast for simplicity). I suppose in theory
>>> that could have a false match, but that could happen in this patch
>>> already.
>> I think if any other kernel code put of_pci_free_node to of_node->data, it
>> can be fixed over there.
>>
>>>> Do you mean to add a flag (e.g. OF_PCI_DYNAMIC) to
>>>> indicate of_node->data points to cset?
>>> That would be another option, but OF_PCI_DYNAMIC would not be a good
>>> name because that would be a flag bit for every single caller needing
>>> similar functionality. Name it just what it indicates: of_node->data
>>> points to cset
>>>
>>> If we have that flag, then possibly the DT core can handle more
>>> clean-up itself like calling detach and freeing the changeset.
>>> Ideally, the flags should be internal to the DT code.
>> Sure. If you prefer this option, I will propose another fix.
>>
> The crash in question is a critical issue that we would want to have a fix for
> soon. And while this is still being figured out, is it okay to go with the fix I
> proposed in the V1 of this patch?
>
> Thanks,
> Amit
>
>> Thanks,
>>
>> Lizhi
>>
>>> Rob
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