Re: [PATCH v2] PCI: Fix crash during pci_dev hot-unplug on pseries KVM guest
From: Lizhi Hou
Date: Mon Jul 15 2024 - 16:52:52 EST
On 7/15/24 11:55, Rob Herring wrote:
On Mon, Jul 15, 2024 at 2:08 AM Amit Machhiwal <amachhiw@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
Signed-off-by: Lizhi Hou <lizhi.hou@xxxxxxx>
Signed-off-by: Amit Machhiwal <amachhiw@xxxxxxxxxxxxx>
---
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@xxxxxxxxxxxxx/
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?
Thanks,
Lizhi
Rob