CVE-2024-26806

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

spi: cadence-qspi: remove system-wide suspend helper calls from runtime PM hooks

The ->runtime_suspend() and ->runtime_resume() callbacks are not
expected to call spi_controller_suspend() and spi_controller_resume().
Remove calls to those in the cadence-qspi driver.

Those helpers have two roles currently:

• They stop/start the queue, including dealing with the kworker.
• They toggle the SPI controller SPI_CONTROLLER_SUSPENDED flag. It
  requires acquiring ctlr->bus_lock_mutex.

Step one is irrelevant because cadence-qspi is not queued. Step two
however has two implications:

• A deadlock occurs, because ->runtime_resume() is called in a context
  where the lock is already taken (in the ->exec_op() callback, where
  the usage count is incremented).
• It would disallow all operations once the device is auto-suspended.

Here is a brief call tree highlighting the mutex deadlock:

spi_mem_exec_op()
…
spi_mem_access_start()
mutex_lock(&ctlr->bus_lock_mutex)

    cqspi_exec_mem_op()
            pm_runtime_resume_and_get()
                    cqspi_resume()
                            spi_controller_resume()
                                    mutex_lock(&ctlr->bus_lock_mutex)
            ...

    spi_mem_access_end()
            mutex_unlock(&ctlr->bus_lock_mutex)
    ...