CVE-2026-90338: serial: amba-pl011: keep console clock enabled for atomic writes

CVE-2026-90338: serial: amba-pl011: keep console clock enabled for atomic writes

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2026-90338 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.15 with commit 2eb2608618ce5878e11bbe68cc8d2699c8f3a81a and fixed in 6.18.52 with commit 5b77848423f4a5a362dcc3caedcdc1a75d0758c3
	Issue introduced in 6.15 with commit 2eb2608618ce5878e11bbe68cc8d2699c8f3a81a and fixed in 7.2.6 with commit 2ad24c1d0b939d814a3020f96a667ac2d0394289
	Issue introduced in 6.15 with commit 2eb2608618ce5878e11bbe68cc8d2699c8f3a81a and fixed in 7.3-rc1 with commit c0e8cfef754645856374e82c8effd54b7d82002b

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-90338
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/tty/serial/amba-pl011.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/5b77848423f4a5a362dcc3caedcdc1a75d0758c3
	https://git.kernel.org/stable/c/2ad24c1d0b939d814a3020f96a667ac2d0394289
	https://git.kernel.org/stable/c/c0e8cfef754645856374e82c8effd54b7d82002b