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 ->runtimesuspend() and ->runtimeresume() callbacks are not expected to call spicontrollersuspend() and spicontrollerresume(). 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 SPICONTROLLERSUSPENDED flag. It requires acquiring ctlr->buslockmutex.

Step one is irrelevant because cadence-qspi is not queued. Step two however has two implications: - A deadlock occurs, because ->runtimeresume() is called in a context where the lock is already taken (in the ->execop() 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:

spimemexecop() ... spimemaccessstart() mutexlock(&ctlr->buslock_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)
    ...