[PATCH v2] PCI: Fix crash during pci_dev hot-unplug on pseries KVM guest
Lizhi Hou
lizhi.hou at amd.com
Tue Jul 16 02:20:01 AEST 2024
On 7/15/24 01:07, 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 `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);
> + }
> +
> np->parent = parent;
>
> ret = of_changeset_attach_node(ocs, np);
> diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
> index 445ad13dab98..b1bcc9ed40a6 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/bus.c b/drivers/pci/bus.c
> index 826b5016a101..d7ca20cb146a 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -342,8 +342,7 @@ void pci_bus_add_device(struct pci_dev *dev)
> */
> pcibios_bus_add_device(dev);
> pci_fixup_device(pci_fixup_final, dev);
> - if (pci_is_bridge(dev))
> - of_pci_make_dev_node(dev);
> + of_pci_make_dev_node(dev);
Please undo this change. It should only create the device node for
bridges and the pci endpoints listed in quirks for now.
Thanks,
Lizhi
> pci_create_sysfs_dev_files(dev);
> pci_proc_attach_device(dev);
> pci_bridge_d3_update(dev);
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index 51e3dd0ea5ab..883bf15211a5 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)
> @@ -670,19 +684,18 @@ void of_pci_make_dev_node(struct pci_dev *pdev)
>
> ret = of_changeset_apply(cset);
> if (ret)
> - goto out_free_node;
> + goto out_destroy_cset;
>
> - np->data = cset;
> + np->data = of_pci_free_node;
> pdev->dev.of_node = np;
> - kfree(name);
>
> return;
>
> -out_free_node:
> - of_node_put(np);
> out_destroy_cset:
> of_changeset_destroy(cset);
> kfree(cset);
> +out_free_node:
> + of_node_put(np);
> out_free_name:
> kfree(name);
> }
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index fd44565c4756..7b1a455306b8 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -702,11 +702,13 @@ struct of_changeset;
>
> #ifdef CONFIG_PCI_DYNAMIC_OF_NODES
> void of_pci_make_dev_node(struct pci_dev *pdev);
> +void of_pci_free_node(struct device_node *np);
> void of_pci_remove_node(struct pci_dev *pdev);
> int of_pci_add_properties(struct pci_dev *pdev, struct of_changeset *ocs,
> struct device_node *np);
> #else
> static inline void of_pci_make_dev_node(struct pci_dev *pdev) { }
> +static inline void of_pci_free_node(struct device_node *np) { }
> static inline void of_pci_remove_node(struct pci_dev *pdev) { }
> #endif
>
> 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,
>
> base-commit: 43db1e03c086ed20cc75808d3f45e780ec4ca26e
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