Vulnerability CVE-2021-47617
Published: 2024-06-20

Description:
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
pciehp's 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.

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