From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 27776168B5; Fri, 12 Jan 2024 09:40:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="WlVKOnSW" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1705052414; x=1736588414; h=from:date:to:cc:subject:in-reply-to:message-id: references:mime-version; bh=mYZ8szFmxn+ynEuSW/tRuoGiph0TTNr3kjNUdauc12s=; b=WlVKOnSWgY91qw3lIjkeAPJe9c9gnGP9HkRkM6bhU1FqVQ01fvLT0uOA pfnXSEj7rvF/p4MNpfaqoidCyLsmcuOH4b8s0v9TjKtCuyxl3pK/lIHYx cwwUkuBnTrseJgQokEeo+mtkXvJ73x5Ol6MU7ls7rCXLr+DeZT5G2SfRV FsqylqPgXjnRx1cQknHk0AJ5sZDluC74KZMDIBp/2noc/BXFKiHJDQh/H GZ4XGfo80EiOaigNDAVVg/fQ0bbxPtChLk7tKjtFU/BkxwU4hsrYZXZDD 5oHf1lBEk+WiWRbpCtR/f0zW+JC2chfUy537R6Anobcn9sNcb4jpV7RG1 Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10950"; a="6493353" X-IronPort-AV: E=Sophos;i="6.04,189,1695711600"; d="scan'208";a="6493353" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jan 2024 01:40:13 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10950"; a="786283497" X-IronPort-AV: E=Sophos;i="6.04,189,1695711600"; d="scan'208";a="786283497" Received: from ijarvine-desk1.ger.corp.intel.com (HELO localhost) ([10.246.33.141]) by fmsmga007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jan 2024 01:40:08 -0800 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Date: Fri, 12 Jan 2024 11:40:04 +0200 (EET) To: John Ogness cc: Gui-Dong Han <2045gemini@gmail.com>, Greg Kroah-Hartman , Jiri Slaby , Tony Lindgren , l.sanfilippo@kunbus.com, tglx@linutronix.de, Andy Shevchenko , LKML , linux-serial , baijiaju1990@outlook.com, stable@vger.kernel.org Subject: Re: [PATCH] serial: core: Fix atomicity violation in uart_tiocmget In-Reply-To: <87msta7vbe.fsf@jogness.linutronix.de> Message-ID: <4a52df23-71c3-59c7-fee4-e7cde526d249@linux.intel.com> References: <20240112075732.16730-1-2045gemini@gmail.com> <87msta7vbe.fsf@jogness.linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Fri, 12 Jan 2024, John Ogness wrote: > On 2024-01-12, Gui-Dong Han <2045gemini@gmail.com> wrote: > > In uart_tiocmget(): > > result = uport->mctrl; > > uart_port_lock_irq(uport); > > result |= uport->ops->get_mctrl(uport); > > uart_port_unlock_irq(uport); > > ... > > return result; > > > > In uart_update_mctrl(): > > uart_port_lock_irqsave(port, &flags); > > ... > > port->mctrl = (old & ~clear) | set; > > ... > > uart_port_unlock_irqrestore(port, flags); > > > > An atomicity violation is identified due to the concurrent execution of > > uart_tiocmget() and uart_update_mctrl(). After assigning > > result = uport->mctrl, the mctrl value may change in uart_update_mctrl(), > > leading to a mismatch between the value returned by > > uport->ops->get_mctrl(uport) and the mctrl value previously read. > > This can result in uart_tiocmget() returning an incorrect value. > > > > This possible bug is found by an experimental static analysis tool > > developed by our team, BassCheck[1]. This tool analyzes the locking APIs > > to extract function pairs that can be concurrently executed, and then > > analyzes the instructions in the paired functions to identify possible > > concurrency bugs including data races and atomicity violations. The above > > possible bug is reported when our tool analyzes the source code of > > Linux 5.17. > > > > To address this issue, it is suggested to move the line > > result = uport->mctrl inside the uart_port_lock block to ensure atomicity > > and prevent the mctrl value from being altered during the execution of > > uart_tiocmget(). With this patch applied, our tool no longer reports the > > bug, with the kernel configuration allyesconfig for x86_64. Due to the > > absence of the requisite hardware, we are unable to conduct runtime > > testing of the patch. Therefore, our verification is solely based on code > > logic analysis. > > > > [1] https://sites.google.com/view/basscheck/ > > > > Fixes: 559c7ff4e324 ("serial: core: Use port lock wrappers") > > It fixes c5f4644e6c8b ("[PATCH] Serial: Adjust serial locking"). That commit only extracted the locks from ->get_mctrl() into the caller but this assignment was outside both pre and post that commit (the issue goes all the way back into history.git domain into 33c0d1b0c3eb ("[PATCH] Serial driver stuff") which introduced ->mctrl). -- i. > > Cc: stable@vger.kernel.org > > Signed-off-by: Gui-Dong Han <2045gemini@gmail.com> > > --- > > drivers/tty/serial/serial_core.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c > > index 80085b151b34..a9e39416d877 100644 > > --- a/drivers/tty/serial/serial_core.c > > +++ b/drivers/tty/serial/serial_core.c > > @@ -1085,8 +1085,8 @@ static int uart_tiocmget(struct tty_struct *tty) > > goto out; > > > > if (!tty_io_error(tty)) { > > - result = uport->mctrl; > > uart_port_lock_irq(uport); > > + result = uport->mctrl; > > result |= uport->ops->get_mctrl(uport); > > uart_port_unlock_irq(uport); > > } > > Looking over the RMW accesses to @mctrl, I expect you will also need > this hunk: > > @@ -2242,6 +2242,7 @@ uart_set_options(struct uart_port *port, struct console *co, > { > struct ktermios termios; > static struct ktermios dummy; > + unsigned long flags; > > /* > * Ensure that the serial-console lock is initialised early. > @@ -2279,7 +2280,9 @@ uart_set_options(struct uart_port *port, struct console *co, > * some uarts on other side don't support no flow control. > * So we set * DTR in host uart to make them happy > */ > + uart_port_lock_irqsave(port, &flags); > port->mctrl |= TIOCM_DTR; > + uart_port_unlock_irqrestore(port, flags); > > port->ops->set_termios(port, &termios, &dummy); > /* > > FWIW, > Reviewed-by: John Ogness >