Re: [PATCH v3] PCI: Fix crash during pci_dev hot-unplug on pseries KVM guest
From: Bjorn Helgaas <helgaas@kernel.org>
Date: 2024-08-06 20:01:01
Also in:
linux-devicetree, linux-pci, lkml
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.
quoted hunk ↗ jump to hunk
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 <redacted> Signed-off-by: Lizhi Hou <lizhi.hou@amd.com> Signed-off-by: Amit Machhiwal <redacted> --- 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@linux.ibm.com/ (local) 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/ (local) 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.
quoted hunk ↗ jump to hunk
@@ -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.