On Sat, Aug 03, 2024 at 12:03:25AM +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:
What is unique about pseries here? There's nothing specific to
pseries in the patch, so I would expect this to be a generic problem
on any arch.
> 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
Weird address. I would expect NULL or something. Where did this
non-NULL pointer come from?
> 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.
I'm sure this description is 100% correct, but it's at such a low
level that it doesn't really help understand the underlying design
problem.
Will need an ack from Rob.
> 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@xxxxxxxxxxxxx>
> Signed-off-by: Lizhi Hou <lizhi.hou@xxxxxxx>
> Signed-off-by: Amit Machhiwal <amachhiw@xxxxxxxxxxxxx>
> ---
> 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@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/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;
of_pci_remove_node() goes on to call of_changeset_revert() and
of_changeset_destroy(). of_pci_remove_node() has nothing PCI-specific
in it.
There are a few other callers of of_changeset_destroy(), but they
don't look anything like of_pci_remove_node(). Seems like there
should be some similarity across the callers, so it makes me a little
nervous that there isn't.
> @@ -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 */
Follow existing capitalization style.
