From: Ryan Wilbur <rwilbur633@gmail.com> mainline inclusion from mainline-v7.2-rc7 commit 1423415471274abda87024967d7fe2206ceee0ea category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/18269 CVE: CVE-2026-74653 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- The NXP LPC32xx UART (PORT_LPC3220) can latch an RX character-timeout interrupt while the RX FIFO is empty: IIR reports UART_IIR_RX_TIMEOUT (0x0c) but LSR.DR is clear. A character timeout is only cleared by reading RHR, but serial8250_rx_chars() reads RHR only when LSR.DR is set, so nothing ever clears the condition. The interrupt is level-triggered and re-fires immediately, so on a single-core ARM926 the resulting interrupt storm livelocks the CPU. It is reproducible when userspace repeatedly opens the front-panel port (ttyS1): serial8250_do_set_termios() re-enables interrupts on unlock and the handler then spins forever with iir=0xcc lsr=0x60 ier=0x05, tripping the soft-lockup detector in serial8250_handle_irq_locked(). LPC32xx has no dedicated 8250 glue driver, it's driven by the generic 8250_of. Add a hardware specific handle_irq for PORT_LPC3220, wired up in of_platform_serial_setup() the same way fsl8250_handle_irq is installed. The handler follows dw8250_handle_irq(): on an RX timeout with an empty FIFO (LSR.DR and LSR.BI clear) it does one throwaway RHR read to clear the condition, then calls serial8250_handle_irq_locked(). No real received data is ever discarded, and it is a no-op on healthy UARTs which never report a timeout with DR clear. This is the same class of bug already worked around in other 8250 drivers; see commit 424d79183af0 ("serial: 8250_dw: Avoid "too much work" from bogus rx timeout interrupt") which reports the identical iir=0xcc/lsr=0x60. See also UART_RX_TIMEOUT_QUIRK in 8250_omap, and the note in 8250_bcm7271. Cc: stable <stable@kernel.org> Assisted-by: Claude:Opus4.8 Signed-off-by: Ryan Wilbur <rwilbur633@gmail.com> Link: https://patch.msgid.link/20260730193920.28954-1-rwilbur633@gmail.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Conflicts: drivers/tty/serial/8250/8250_of.c [There is no guard(xxx) in 6.6. Restore it to the method of locking and unlocking. The commit cdd30ebb1b9f ("module: Convert symbol namespace to string literal") is not merged, thus MODULE_IMPORT_NS should not add "". Others are only context conflicts.] Signed-off-by: Cai Xinchen <caixinchen1@huawei.com> --- drivers/tty/serial/8250/8250_of.c | 44 +++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+) diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c index 51329625c48a..aec3cb0a3fb5 100644 --- a/drivers/tty/serial/8250/8250_of.c +++ b/drivers/tty/serial/8250/8250_of.c @@ -25,6 +25,46 @@ struct of_serial_info { int line; }; +static int lpc32xx_handle_irq(struct uart_port *port) +{ + struct uart_8250_port *up = up_to_u8250p(port); + unsigned int iir; + u16 status; + unsigned long flags; + + serial8250_rpm_get(up); + + iir = serial_port_in(port, UART_IIR); + if (iir & UART_IIR_NO_INT) { + serial8250_rpm_put(up); + return 0; + } + + uart_port_lock_irqsave(port, &flags); + + /* + * The LPC32xx UART can assert an RX character-timeout interrupt while + * the RX FIFO is empty: IIR reports UART_IIR_RX_TIMEOUT but LSR.DR is + * clear. The timeout is only cleared by reading RHR, but the core RX + * path skips that read when the FIFO is empty, so the level-triggered + * IRQ re-fires forever and livelocks this single-core SoC. Do one + * throwaway RHR read to clear it; a healthy UART never reports a + * timeout with DR/BI clear, so no received data is ever discarded. + */ + if ((iir & 0x3f) == UART_IIR_RX_TIMEOUT) { + status = serial_lsr_in(up); + if (!(status & (UART_LSR_DR | UART_LSR_BI))) + serial_port_in(port, UART_RX); + } + + serial8250_handle_irq_locked(port, iir); + + uart_unlock_and_check_sysrq_irqrestore(port, flags); + serial8250_rpm_put(up); + + return 1; +} + /* * Fill a struct uart_port for a given device node */ @@ -175,6 +215,9 @@ static int of_platform_serial_setup(struct platform_device *ofdev, if (ret) goto err_unprepare; break; + case PORT_LPC3220: + port->handle_irq = lpc32xx_handle_irq; + break; } if (IS_REACHABLE(CONFIG_SERIAL_8250_FSL) && @@ -354,6 +397,7 @@ static struct platform_driver of_platform_serial_driver = { module_platform_driver(of_platform_serial_driver); +MODULE_IMPORT_NS(SERIAL_8250); MODULE_AUTHOR("Arnd Bergmann <arnd@arndb.de>"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("Serial Port driver for Open Firmware platform devices"); -- 2.18.0.huawei.25