UBUNTU-CVE-2026-90338: Medium severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: serial: amba-pl011: keep console clock enabled for atomic writes pl011consolewriteatomic() runs from nbcon atomic context, where sleeping is not allowed. It calls clkenable(), which takes the common-clk enablelock. Under PREEMPTRT that is a sleeping lock: clkenablelock() first tries spintrylockirqsave(), but on contention falls back to spinlockirqsave(). Therefore, an atomic-context printk on an RT kernel with a clk-backed pl011 can trip: BUG: sleeping function called from invalid context at spinlockrt.c:48 mightresched from rtspinlock rtspinlock from clkenablelock clkenablelock from clkenable clkenable from pl011consolewriteatomic ... from vprintkemit This was found and reproduced on PREEMPTRT. Arm32 and arm64 DT SoCs are affected; arm64 SBSA/ACPI has no clk, so clkenable(NULL) short-circuits before the lock. In addition, writeatomic() may be invoked from NMI context and is documented to avoid locking. Removing clkenable() from the callback also avoids a potentially unsafe NMI acquisition of the common-clock enablelock. 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 clkprepareenable() in pl011consolesetup(), release it via clkdisableunprepare() in the console .exit() callback, and drop the per-write clkenable()/clkdisable() pairs from writeatomic() and writethread(). When printk suspends consoles, drop the reference after uartsuspendport() stops console access and restore it before uartresumeport() -- but only if suspend actually marked the port suspended (a wake-capable tty stays running and must keep its clock), and keep it when consolesuspendenabled is false so noconsolesuspend 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.