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Message-ID: <87d645e3-69ac-170d-bdc2-26bc3c03b890@amd.com>
Date: Mon, 15 Jul 2024 09:20:01 -0700
From: Lizhi Hou <lizhi.hou@....com>
To: Amit Machhiwal <amachhiw@...ux.ibm.com>, <linux-pci@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>
CC: <linuxppc-dev@...ts.ozlabs.org>, <kvm-ppc@...r.kernel.org>, Bjorn Helgaas
	<bhelgaas@...gle.com>, Rob Herring <robh@...nel.org>, Saravana Kannan
	<saravanak@...gle.com>, Vaibhav Jain <vaibhav@...ux.ibm.com>, Nicholas Piggin
	<npiggin@...il.com>, Michael Ellerman <mpe@...erman.id.au>, "Vaidyanathan
 Srinivasan" <svaidy@...ux.ibm.com>, Kowshik Jois B S
	<kowsjois@...ux.ibm.com>, Lukas Wunner <lukas@...ner.de>
Subject: Re: [PATCH v2] PCI: Fix crash during pci_dev hot-unplug on pseries
 KVM guest


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@...ux.ibm.com>
> Signed-off-by: Lizhi Hou <lizhi.hou@....com>
> Signed-off-by: Amit Machhiwal <amachhiw@...ux.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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