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CVE-2025-21820 – Xilinx tty UART Lock Deadlock Vulnerability

The following table lists the changes that have been made to the
CVE-2025-21820 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution
of a vulnerability, and for identifying the most recent changes that may
impact the vulnerability’s severity, exploitability, or other characteristics.

  • New CVE Received
    by 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    Feb. 27, 2025

    Action Type Old Value New Value
    Added Description In the Linux kernel, the following vulnerability has been resolved:

    tty: xilinx_uartps: split sysrq handling

    lockdep detects the following circular locking dependency:

    CPU 0 CPU 1
    ========================== ============================
    cdns_uart_isr() printk()
    uart_port_lock(port) console_lock()
    cdns_uart_console_write()
    if (!port->sysrq)
    uart_port_lock(port)
    uart_handle_break()
    port->sysrq = …
    uart_handle_sysrq_char()
    printk()
    console_lock()

    The fixed commit attempts to avoid this situation by only taking the
    port lock in cdns_uart_console_write if port->sysrq unset. However, if
    (as shown above) cdns_uart_console_write runs before port->sysrq is set,
    then it will try to take the port lock anyway. This may result in a
    deadlock.

    Fix this by splitting sysrq handling into two parts. We use the prepare
    helper under the port lock and defer handling until we release the lock.
    Added Reference https://git.kernel.org/stable/c/4410dba9807a17a93f649a9f5870ceaf30a675a3
    Added Reference https://git.kernel.org/stable/c/8ea0e7b3d7b8f2f0fc9db491ff22a0abe120801c
    Added Reference https://git.kernel.org/stable/c/9b88a7c4584ba67267a051069b8abe44fc9595b2
    Added Reference https://git.kernel.org/stable/c/b06f388994500297bb91be60ffaf6825ecfd2afe
    Added Reference https://git.kernel.org/stable/c/de5bd24197bd9ee37ec1e379a3d882bbd15c5065
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