CVE-2026-90338
UnknownSummary
A vulnerability exists in the Linux kernel's amba-pl011 serial console driver. The pl011_console_write_atomic() function runs in nbcon atomic context and calls clk_enable(), which under PREEMPT_RT can sleep, triggering a "sleeping function called from invalid context" bug. This affects arm32 and arm64 Device Tree SoCs where the UART uses a common-clk managed clock.
Risk Assessment
On PREEMPT_RT systems, an atomic-context printk (e.g., from NMI) can cause a kernel bug and system hang. It may also lead to an unsafe NMI acquisition of the common-clock enable_lock.
Recommendation
Update the Linux kernel to a version containing the fix that moves clock enabling to pl011_console_setup() and releases it in the console .exit() callback. If updating is not possible, avoid PREEMPT_RT configurations with pl011 console or limit atomic-context printk calls.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: serial: amba-pl011: keep console clock enabled for atomic writes pl011_console_write_atomic() runs from nbcon atomic context, where sleeping is not allowed. It calls clk_enable(), which takes the common-clk enable_lock. Under PREEMPT_RT that is a sleeping lock: clk_enable_lock() first tries spin_trylock_irqsave(), but on contention falls back to spin_lock_irqsave(). Therefore, an atomic-context printk on an RT kernel with a clk-backed pl011 can trip: BUG: sleeping function called from invalid context at spinlock_rt.c:48 __might_resched from rt_spin_lock rt_spin_lock from clk_enable_lock clk_enable_lock from clk_enable clk_enable from pl011_console_write_atomic ... from vprintk_emit This was found and reproduced on PREEMPT_RT. Arm32 and arm64 DT SoCs are affected; arm64 SBSA/ACPI has no clk, so clk_enable(NULL) short-circuits before the lock. In addition, write_atomic() may be invoked from NMI context and is documented to avoid locking. Removing clk_enable() from the callback also avoids a potentially unsafe NMI acquisition of the common-clock enable_lock. An nbcon atomic-capable console must be printable from any context, so the clock cannot be gated between writes. Enable the clock while the console is available for output: use clk_prepare_enable() in pl011_console_setup(), release it via clk_disable_unprepare() in the console .exit() callback, and drop the per-write clk_enable()/clk_disable() pairs from write_atomic() and write_thread(). When printk suspends consoles, drop the reference after uart_suspend_port() stops console access and restore it before uart_resume_port() -- but only if suspend actually marked the port suspended (a wake-capable tty stays running and must keep its clock), and keep it when console_suspend_enabled is false so no_console_suspend works. The active power cost of keeping the clock enabled is platform-dependent: none where the UART clock is a fixed always-on oscillator, real where it is a gateable clock branch, which then cannot be gated (nor possibly can its parent clocks) while the console is available for output. When serial core actually suspends the port, the reference is released so the clock provider can gate the clock tree.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS