From mboxrd@z Thu Jan 1 00:00:00 1970 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 38ED1C33CA2 for ; Thu, 9 Jan 2020 21:55:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 02FBC2077B for ; Thu, 9 Jan 2020 21:55:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="mHJoCq0I" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729261AbgAIVzR (ORCPT ); Thu, 9 Jan 2020 16:55:17 -0500 Received: from mail-pl1-f193.google.com ([209.85.214.193]:40204 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729191AbgAIVzQ (ORCPT ); Thu, 9 Jan 2020 16:55:16 -0500 Received: by mail-pl1-f193.google.com with SMTP id s21so1202plr.7 for ; Thu, 09 Jan 2020 13:55:15 -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=0t7GY6iSUUJjTNq+571aHFfJqJAb8s1IuRDcFTf/E44=; b=mHJoCq0IIBFpUNEH5TNsxx2Mdg9Kp9foE409HrV8dHsT/E4UFq2VGrpwkcBaMNfwAG FPCN6CE701wFATLa9eCoWonTQVXQKKsm8v1PHLkhl7JtUvyhBVoeeX+nNEXNV+jD9fVP A6/etzJFI1ZdSjp2bd8DchmM7T+hqznrY5Qw6piob5vdk6Utqb6a4nGBHUbIH8nDV1xO jEwkacqEFHo5dPZ6cnktqnFZCmajRaLCsQz8ykyWwlL0SnEQMeKvGM9g6xHtkV8KNGWI KqWQIk8sdTrhoiITCbToQqw7/vuLVRLXpeOpMuRsQzNqSffXaTxrVE9SBPuIXCMzq0ZH 9Mgg== 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=0t7GY6iSUUJjTNq+571aHFfJqJAb8s1IuRDcFTf/E44=; b=eSgqM7CuO+yhyaN4PWP/WAxTijywgSrwgBMwHCC23mrMQlvjTdIOoqYwPifRqqQC/I /wvuA9hL6kUC/qc4NRkct8Ep7Dqa0Y6M3VWy7QBqqS2prd31f46uSQE2hD6pPLZO2wKy S1mT/qPJiNDsJwN/hkCkxy6+ZlAMl1c7wYjTo1krxwf5nxVdmh1ol3CVQ2HLuvDVBC4L qCgl/yl22qs7E9imzOUoRG/mBxXyB6+qj87q6BEysWM+J0orr1YgUz/b1n3Jx8N7yYux USxPS+qcBvBV6n/0y+eYXyqPYtW4QkN1+6/bokqr02mE6+NnQ/NqO66e3JkL0POCvP62 Z6Fw== X-Gm-Message-State: APjAAAVtlVjYNK2YCvx49zWLDKFpJ9eX7MFiTwB93jmIfiRxUQHyoKQ8 uXLvobAGgi7NOewmvV0xPjk+mwkzem4= X-Google-Smtp-Source: APXvYqwE8mz5Ea5w1E08qFqHvPBY8vLXirpMFLgZXzw8CUgYKwU1ONgqf4eVhGrAwj8q/Y8ewVaVHg== X-Received: by 2002:a17:902:8497:: with SMTP id c23mr141511plo.59.1578606914837; Thu, 09 Jan 2020 13:55:14 -0800 (PST) Received: from Mindolluin.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id r20sm8711536pgu.89.2020.01.09.13.55.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Jan 2020 13:55:14 -0800 (PST) From: Dmitry Safonov To: linux-kernel@vger.kernel.org Cc: Dmitry Safonov <0x7f454c46@gmail.com>, Dmitry Safonov , Greg Kroah-Hartman , Jiri Slaby , Vasiliy Khoruzhick , linux-serial@vger.kernel.org Subject: [PATCH-next 3/3] serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE Date: Thu, 9 Jan 2020 21:54:44 +0000 Message-Id: <20200109215444.95995-4-dima@arista.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200109215444.95995-1-dima@arista.com> References: <20200109215444.95995-1-dima@arista.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 | 52 ++++++++++++++++++++++++++++---- include/linux/serial_core.h | 2 +- lib/Kconfig.debug | 8 +++++ 3 files changed, 55 insertions(+), 7 deletions(-) diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 6ac9dfed3423..f70eba032d0b 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -3081,6 +3081,38 @@ void uart_insert_char(struct uart_port *port, unsigned int status, } EXPORT_SYMBOL_GPL(uart_insert_char); +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 sequience on serial\n"); +} +static DECLARE_WORK(sysrq_enable_work, uart_sysrq_on); + +static int uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch) +{ + if (sysrq_toggle_seq[0] == '\0') + return 0; + + BUILD_BUG_ON(ARRAY_SIZE(sysrq_toggle_seq) >= sizeof(port->sysrq_seq)*U8_MAX); + if (sysrq_toggle_seq[port->sysrq_seq] != ch) { + port->sysrq_seq = 0; + return 0; + } + + /* Without the last \0 */ + if (++port->sysrq_seq < (ARRAY_SIZE(sysrq_toggle_seq) - 1)) { + port->sysrq = jiffies + HZ*5; + return 1; + } + + schedule_work(&sysrq_enable_work); + + port->sysrq = 0; + return 1; +} + int uart_handle_sysrq_char(struct uart_port *port, unsigned int ch) { if (!IS_ENABLED(CONFIG_MAGIC_SYSRQ_SERIAL)) @@ -3090,9 +3122,13 @@ 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_get_mask()) { + handle_sysrq(ch); + port->sysrq = 0; + return 1; + } + if (uart_try_toggle_sysrq(port, ch)) + return 1; } port->sysrq = 0; @@ -3109,9 +3145,13 @@ 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_get_mask()) { + port->sysrq_ch = ch; + port->sysrq = 0; + return 1; + } + if (uart_try_toggle_sysrq(port, ch)) + return 1; } port->sysrq = 0; diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h index 255e86a474e9..1f4443db5474 100644 --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -243,10 +243,10 @@ 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; - unsigned char unused; const char *name; /* port name */ struct attribute_group *attr_group; /* port specific attributes */ const struct attribute_group **tty_groups; /* all attributes (serial core use only) */ diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 330909c600b1..f6f3e82fee25 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 -- 2.24.1