CVE-2024-26605

In the Linux kernel, the following vulnerability has been resolved:

PCI/ASPM: Fix deadlock when enabling ASPM

A last minute revert in 6.7-final introduced a potential deadlock when enabling ASPM during probe of Qualcomm PCIe controllers as reported by lockdep:

============================================ WARNING: possible recursive locking detected 6.7.0 #40 Not tainted

kworker/u16:5/90 is trying to acquire lock: ffffacfa78ced000 (pcibussem){++++}-{3:3}, at: pcieaspmpmstatechange+0x58/0xdc

          but task is already holding lock:

ffffacfa78ced000 (pcibussem){++++}-{3:3}, at: pciwalkbus+0x34/0xbc

          other info that might help us debug this:

Possible unsafe locking scenario:

     CPU0
     ----
lock(pci_bus_sem);
lock(pci_bus_sem);

           *** DEADLOCK ***

Call trace: printdeadlockbug+0x25c/0x348 _lockacquire+0x10a4/0x2064 lockacquire+0x1e8/0x318 downread+0x60/0x184 pcieaspmpmstatechange+0x58/0xdc pcisetfullpowerstate+0xa8/0x114 pcisetpowerstate+0xc4/0x120 qcompcieenableaspm+0x1c/0x3c [pcieqcom] pciwalkbus+0x64/0xbc qcompciehostpostinit270+0x28/0x34 [pcie_qcom]

The deadlock can easily be reproduced on machines like the Lenovo ThinkPad X13s by adding a delay to increase the race window during asynchronous probe where another thread can take a write lock.

Add a new pcisetpowerstatelocked() and associated helper functions that can be called with the PCI bus semaphore held to avoid taking the read lock twice.