Patch "PCI/ASPM: Disable ASPM on MFD function removal to avoid use-after-free" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    PCI/ASPM: Disable ASPM on MFD function removal to avoid use-after-free

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     pci-aspm-disable-aspm-on-mfd-function-removal-to-avo.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a2c77802943704838b8d41b060ca5af8e2387aee
Author: Ding Hui <dinghui@xxxxxxxxxxxxxx>
Date:   Sun May 7 11:40:57 2023 +0800

    PCI/ASPM: Disable ASPM on MFD function removal to avoid use-after-free
    
    [ Upstream commit 456d8aa37d0f56fc9e985e812496e861dcd6f2f2 ]
    
    Struct pcie_link_state->downstream is a pointer to the pci_dev of function
    0.  Previously we retained that pointer when removing function 0, and
    subsequent ASPM policy changes dereferenced it, resulting in a
    use-after-free warning from KASAN, e.g.:
    
      # echo 1 > /sys/bus/pci/devices/0000:03:00.0/remove
      # echo powersave > /sys/module/pcie_aspm/parameters/policy
    
      BUG: KASAN: slab-use-after-free in pcie_config_aspm_link+0x42d/0x500
      Call Trace:
       kasan_report+0xae/0xe0
       pcie_config_aspm_link+0x42d/0x500
       pcie_aspm_set_policy+0x8e/0x1a0
       param_attr_store+0x162/0x2c0
       module_attr_store+0x3e/0x80
    
    PCIe spec r6.0, sec 7.5.3.7, recommends that software program the same ASPM
    Control value in all functions of multi-function devices.
    
    Disable ASPM and free the pcie_link_state when any child function is
    removed so we can discard the dangling pcie_link_state->downstream pointer
    and maintain the same ASPM Control configuration for all functions.
    
    [bhelgaas: commit log and comment]
    Debugged-by: Zongquan Qin <qinzongquan@xxxxxxxxxxxxxx>
    Suggested-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
    Fixes: b5a0a9b59c81 ("PCI/ASPM: Read and set up L1 substate capabilities")
    Link: https://lore.kernel.org/r/20230507034057.20970-1-dinghui@xxxxxxxxxxxxxx
    Signed-off-by: Ding Hui <dinghui@xxxxxxxxxxxxxx>
    Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index ac0557a305aff..51da8ba67d216 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -993,21 +993,24 @@ void pcie_aspm_exit_link_state(struct pci_dev *pdev)
 
 	down_read(&pci_bus_sem);
 	mutex_lock(&aspm_lock);
-	/*
-	 * All PCIe functions are in one slot, remove one function will remove
-	 * the whole slot, so just wait until we are the last function left.
-	 */
-	if (!list_empty(&parent->subordinate->devices))
-		goto out;
 
 	link = parent->link_state;
 	root = link->root;
 	parent_link = link->parent;
 
-	/* All functions are removed, so just disable ASPM for the link */
+	/*
+	 * link->downstream is a pointer to the pci_dev of function 0.  If
+	 * we remove that function, the pci_dev is about to be deallocated,
+	 * so we can't use link->downstream again.  Free the link state to
+	 * avoid this.
+	 *
+	 * If we're removing a non-0 function, it's possible we could
+	 * retain the link state, but PCIe r6.0, sec 7.5.3.7, recommends
+	 * programming the same ASPM Control value for all functions of
+	 * multi-function devices, so disable ASPM for all of them.
+	 */
 	pcie_config_aspm_link(link, 0);
 	list_del(&link->sibling);
-	/* Clock PM is for endpoint device */
 	free_link_state(link);
 
 	/* Recheck latencies and configure upstream links */
@@ -1015,7 +1018,7 @@ void pcie_aspm_exit_link_state(struct pci_dev *pdev)
 		pcie_update_aspm_capable(root);
 		pcie_config_aspm_path(parent_link);
 	}
-out:
+
 	mutex_unlock(&aspm_lock);
 	up_read(&pci_bus_sem);
 }



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