CVE-2021-47617

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

PCI: pciehp: Fix infinite loop in IRQ handler upon power fault

The Power Fault Detected bit in the Slot Status register differs from all other hotplug events in that it is sticky: It can only be cleared after turning off slot power. Per PCIe r5.0, sec. 6.7.1.8:

If a power controller detects a main power fault on the hot-plug slot, it must automatically set its internal main power fault latch […]. The main power fault latch is cleared when software turns off power to the hot-plug slot.

The stickiness used to cause interrupt storms and infinite loops which were fixed in 2009 by commits 5651c48cfafe (PCI pciehp: fix power fault interrupt storm problem) and 99f0169c17f3 (PCI: pciehp: enable software notification on empty slots).

Unfortunately in 2020 the infinite loop issue was inadvertently reintroduced by commit 8edf5332c393 (PCI: pciehp: Fix MSI interrupt race): The hardirq handler pciehp_isr() clears the PFD bit until pciehps power_fault_detected flag is set. That happens in the IRQ thread pciehp_ist(), which never learns of the event because the hardirq handler is stuck in an infinite loop. Fix by setting the power_fault_detected flag already in the hardirq handler.

Affected Software

References

• https://git.kernel.org/stable/c/1db58c6584a72102e98af2e600ea184ddaf2b8af
• https://git.kernel.org/stable/c/23584c1ed3e15a6f4bfab8dc5a88d94ab929ee12
• https://git.kernel.org/stable/c/3b4c966fb156ff3e70b2526d964952ff7c1574d9
• https://git.kernel.org/stable/c/464da38ba827f670deac6500a1de9a4f0f44c41d
• https://git.kernel.org/stable/c/6d6f1f0dac3e3441ecdb1103d4efb11b9ed24dd5
• https://git.kernel.org/stable/c/ff27f7d0333cff89ec85c419f431aca1b38fb16a