RE: [PATCH 4/7] vfio/pci: Create persistent INTx handler

[Tian, Kevin]

> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Sent: Thursday, March 7, 2024 5:15 AM
> 
> A vulnerability exists where the eventfd for INTx signaling can be
> deconfigured, which unregisters the IRQ handler but still allows
> eventfds to be signaled with a NULL context through the SET_IRQS ioctl
> or through unmask irqfd if the device interrupt is pending.
> 
> Ideally this could be solved with some additional locking; the igate
> mutex serializes the ioctl and config space accesses, and the interrupt
> handler is unregistered relative to the trigger, but the irqfd path
> runs asynchronous to those.  The igate mutex cannot be acquired from the
> atomic context of the eventfd wake function.  Disabling the irqfd
> relative to the eventfd registration is potentially incompatible with
> existing userspace.
> 
> As a result, the solution implemented here moves configuration of the
> INTx interrupt handler to track the lifetime of the INTx context object
> and irq_type configuration, rather than registration of a particular
> trigger eventfd.  Synchronization is added between the ioctl path and
> eventfd_signal() wrapper such that the eventfd trigger can be
> dynamically updated relative to in-flight interrupts or irqfd callbacks.
> 
> Fixes: 89e1f7d4c66d ("vfio: Add PCI device driver")
> Reported-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>