From patchwork Mon Mar 2 17:51:35 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dmitry Safonov X-Patchwork-Id: 214230 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.9 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0F1ECC3F2D7 for ; Mon, 2 Mar 2020 17:52:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D5E722173E for ; Mon, 2 Mar 2020 17:51:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="EqCK7elF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727202AbgCBRv7 (ORCPT ); Mon, 2 Mar 2020 12:51:59 -0500 Received: from mail-wr1-f67.google.com ([209.85.221.67]:41690 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727341AbgCBRvq (ORCPT ); Mon, 2 Mar 2020 12:51:46 -0500 Received: by mail-wr1-f67.google.com with SMTP id v4so841626wrs.8 for ; Mon, 02 Mar 2020 09:51:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arista.com; s=googlenew; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=0WuDNqRnkyISdiAgs4xnNPd5q/jznPt8vGzOtCd6GYk=; b=EqCK7elFybqQABh5utTaGdkJDVZIiw68QrblpyOsl7K5fLM/IuE22CH46gnlkV1r8I +mPJTEeyiRYxmAyU4zVn/WbGQUzOcW4SY66uRk+ooKk6nTPtvkgcChzccYzM8S+s6gus qd6XhxFJLJjzvGgn+9ic1fA924bzARtHobqlnnoO5H3UqT9VKSM0hDjfNibhkFneI/dR ngmd3s7EPP8NoBKV/++21nXdW7MgPfv06gEhuAgSKHi8FUbgeEsSlApqKRfoMDLLHtvP 2j0svlHpnqCOTxwI8arKfihGMeHf87CoxdzggqmkDeJwqUoPHtaCXECppJ0BmOPZdgb1 Bugg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=0WuDNqRnkyISdiAgs4xnNPd5q/jznPt8vGzOtCd6GYk=; b=qRpbb1J0gvoi8cnpyshdzWKg4djk1DPECDgfZuF5bJrHxBdPc8zwvHq4iD9QmHHI2O uL4hBPoUVn7s9J9LODMDivE/0exX/yR90eGaCiM1qtSEjc5PFX0USGJgZWoAHBDZc8yt TfQPTetG77wg1hMcRu5akOQHTld5wlc92npR0NruV9naCwHRPShMIWwA9P1ibFl0pa43 lJarkkaAwc27wX6Ia2QBNdU7/49dVVbXntGR8wkmdj9nG1/UNLnY6UPN0SPrIOUE0+0W e8P7zwjqzBq4xTJK2M3IGlQngbGZGWAjbQF/zdUidO3HiNpyfbQ/aTnSkB5VtedqYO17 J9gA== X-Gm-Message-State: ANhLgQ1wO/4PeSWfG3uU5mD2CKuyTGEVanZG5D1s1Zbh19Kja7qr7w1W cYcKD5Y4UdloEXqPXu04GLIRbg== X-Google-Smtp-Source: ADFU+vu/W6Nlw7oowUmt5iTvinPfRo+xF6FAklOVJ9JYGbmMSwm64FJ8fZvx8MPTRGu7s32kBFun8w== X-Received: by 2002:a5d:4408:: with SMTP id z8mr676342wrq.321.1583171504513; Mon, 02 Mar 2020 09:51:44 -0800 (PST) Received: from Mindolluin.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id b10sm163234wmh.48.2020.03.02.09.51.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Mar 2020 09:51:43 -0800 (PST) From: Dmitry Safonov To: linux-kernel@vger.kernel.org Cc: Dmitry Safonov <0x7f454c46@gmail.com>, Dmitry Safonov , Greg Kroah-Hartman , Iurii Zaikin , Jiri Slaby , Joe Perches , Randy Dunlap , Vasiliy Khoruzhick , linux-serial@vger.kernel.org Subject: [PATCHv3 2/2] serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE Date: Mon, 2 Mar 2020 17:51:35 +0000 Message-Id: <20200302175135.269397-3-dima@arista.com> X-Mailer: git-send-email 2.25.0 In-Reply-To: <20200302175135.269397-1-dima@arista.com> References: <20200302175135.269397-1-dima@arista.com> MIME-Version: 1.0 Sender: linux-serial-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Many embedded boards have a disconnected TTL level serial which can generate some garbage that can lead to spurious false sysrq detects. Currently, sysrq can be either completely disabled for serial console or always disabled (with CONFIG_MAGIC_SYSRQ_SERIAL), since commit 732dbf3a6104 ("serial: do not accept sysrq characters via serial port") At Arista, we have such boards that can generate BREAK and random garbage. While disabling sysrq for serial console would solve the problem with spurious false sysrq triggers, it's also desirable to have a way to enable sysrq back. As a measure of balance between on and off options, add MAGIC_SYSRQ_SERIAL_SEQUENCE which is a string sequence that can enable sysrq if it follows BREAK on a serial line. The longer the string - the less likely it may be in the garbage. Having the way to enable sysrq was beneficial to debug lockups with a manual investigation in field and on the other side preventing false sysrq detections. Based-on-patch-by: Vasiliy Khoruzhick Signed-off-by: Dmitry Safonov --- drivers/tty/serial/serial_core.c | 75 +++++++++++++++++++++++++++++--- include/linux/serial_core.h | 1 + lib/Kconfig.debug | 8 ++++ 3 files changed, 77 insertions(+), 7 deletions(-) diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 76e506ee335c..83151da74a15 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -20,6 +20,7 @@ #include #include /* for serial_state and serial_icounter_struct */ #include +#include #include #include #include @@ -40,6 +41,8 @@ static struct lock_class_key port_lock_key; #define HIGH_BITS_OFFSET ((sizeof(long)-sizeof(int))*8) +#define SYSRQ_TIMEOUT (HZ * 5) + static void uart_change_speed(struct tty_struct *tty, struct uart_state *state, struct ktermios *old_termios); static void uart_wait_until_sent(struct tty_struct *tty, int timeout); @@ -3082,6 +3085,56 @@ void uart_insert_char(struct uart_port *port, unsigned int status, } EXPORT_SYMBOL_GPL(uart_insert_char); +#ifdef CONFIG_MAGIC_SYSRQ_SERIAL +static const char sysrq_toggle_seq[] = CONFIG_MAGIC_SYSRQ_SERIAL_SEQUENCE; + +static void uart_sysrq_on(struct work_struct *w) +{ + sysrq_toggle_support(1); + pr_info("SysRq is enabled by magic sequence on serial\n"); +} +static DECLARE_WORK(sysrq_enable_work, uart_sysrq_on); + +/** + * uart_try_toggle_sysrq - Enables SysRq from serial line + * @port: uart_port structure where char(s) after BREAK met + * @ch: new character in the sequence after received BREAK + * + * Enables magic SysRq when the required sequence is met on port + * (see CONFIG_MAGIC_SYSRQ_SERIAL_SEQUENCE). + * + * Returns false if @ch is out of enabling sequence and should be + * handled some other way, true if @ch was consumed. + */ +static bool uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch) +{ + if (ARRAY_SIZE(sysrq_toggle_seq) <= 1) + return false; + + BUILD_BUG_ON(ARRAY_SIZE(sysrq_toggle_seq) >= U8_MAX); + if (sysrq_toggle_seq[port->sysrq_seq] != ch) { + port->sysrq_seq = 0; + return false; + } + + /* Without the last \0 */ + if (++port->sysrq_seq < (ARRAY_SIZE(sysrq_toggle_seq) - 1)) { + port->sysrq = jiffies + SYSRQ_TIMEOUT; + return true; + } + + schedule_work(&sysrq_enable_work); + + port->sysrq = 0; + return true; +} +#else +static inline bool uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch) +{ + return false; +} +#endif + int uart_handle_sysrq_char(struct uart_port *port, unsigned int ch) { if (!IS_ENABLED(CONFIG_MAGIC_SYSRQ_SERIAL)) @@ -3091,9 +3144,13 @@ int uart_handle_sysrq_char(struct uart_port *port, unsigned int ch) return 0; if (ch && time_before(jiffies, port->sysrq)) { - handle_sysrq(ch); - port->sysrq = 0; - return 1; + if (sysrq_mask()) { + handle_sysrq(ch); + port->sysrq = 0; + return 1; + } + if (uart_try_toggle_sysrq(port, ch)) + return 1; } port->sysrq = 0; @@ -3110,9 +3167,13 @@ int uart_prepare_sysrq_char(struct uart_port *port, unsigned int ch) return 0; if (ch && time_before(jiffies, port->sysrq)) { - port->sysrq_ch = ch; - port->sysrq = 0; - return 1; + if (sysrq_mask()) { + port->sysrq_ch = ch; + port->sysrq = 0; + return 1; + } + if (uart_try_toggle_sysrq(port, ch)) + return 1; } port->sysrq = 0; @@ -3152,7 +3213,7 @@ int uart_handle_break(struct uart_port *port) if (port->has_sysrq) { if (port->cons && port->cons->index == port->line) { if (!port->sysrq) { - port->sysrq = jiffies + HZ*5; + port->sysrq = jiffies + SYSRQ_TIMEOUT; return 1; } port->sysrq = 0; diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h index 52404ef1694e..1f4443db5474 100644 --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -243,6 +243,7 @@ struct uart_port { unsigned long sysrq; /* sysrq timeout */ unsigned int sysrq_ch; /* char for sysrq */ unsigned char has_sysrq; + unsigned char sysrq_seq; /* index in sysrq_toggle_seq */ unsigned char hub6; /* this should be in the 8250 driver */ unsigned char suspended; diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 69def4a9df00..38a8f3c99579 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -431,6 +431,14 @@ config MAGIC_SYSRQ_SERIAL This option allows you to decide whether you want to enable the magic SysRq key. +config MAGIC_SYSRQ_SERIAL_SEQUENCE + string "Char sequence that enables magic SysRq over serial" + depends on MAGIC_SYSRQ_SERIAL + default "" + help + Specifies a sequence of characters that can follow BREAK to enable + SysRq on a serial console. + config DEBUG_FS bool "Debug Filesystem" help