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
