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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 72266C04AB5 for ; Tue, 4 Jun 2019 03:07:01 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id F3C9426155 for ; Tue, 4 Jun 2019 03:07:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F3C9426155 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=informatik.wtf Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 45HxfV01C8zDqZL for ; Tue, 4 Jun 2019 13:06:58 +1000 (AEST) Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 45Hxcq39BhzDqMy for ; Tue, 4 Jun 2019 13:05:31 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=informatik.wtf Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) by bilbo.ozlabs.org (Postfix) with ESMTP id 45Hxcq2P4fz8vsm for ; Tue, 4 Jun 2019 13:05:31 +1000 (AEST) Received: by ozlabs.org (Postfix) id 45Hxcq25Q1z9s3l; Tue, 4 Jun 2019 13:05:31 +1000 (AEST) Authentication-Results: ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=informatik.wtf (client-ip=198.54.127.52; helo=new-02-3.privateemail.com; envelope-from=cmr@informatik.wtf; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=informatik.wtf Received: from NEW-02-3.privateemail.com (new-02-3.privateemail.com [198.54.127.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 45Hxcp2MCDz9s3Z for ; Tue, 4 Jun 2019 13:05:29 +1000 (AEST) Received: from MTA-06-1.privateemail.com (unknown [10.20.147.16]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by NEW-02.privateemail.com (Postfix) with ESMTPS id 38F3260277; Tue, 4 Jun 2019 03:05:25 +0000 (UTC) Received: from MTA-06.privateemail.com (localhost [127.0.0.1]) by MTA-06.privateemail.com (Postfix) with ESMTP id 22A236003D; Mon, 3 Jun 2019 23:05:25 -0400 (EDT) Received: from APP-01 (unknown [10.20.147.151]) by MTA-06.privateemail.com (Postfix) with ESMTPA id E75D560039; Tue, 4 Jun 2019 03:05:24 +0000 (UTC) Date: Mon, 3 Jun 2019 23:05:24 -0400 (EDT) From: Christopher M Riedl To: Andrew Donnellan , linuxppc-dev@ozlabs.org, kernel-hardening@lists.openwall.com Message-ID: <1146575236.484635.1559617524880@privateemail.com> In-Reply-To: <81549d40-e477-6552-9a12-7200933279af@linux.ibm.com> References: <20190524123816.1773-1-cmr@informatik.wtf> <81549d40-e477-6552-9a12-7200933279af@linux.ibm.com> Subject: Re: [RFC PATCH v2] powerpc/xmon: restrict when kernel is locked down MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Priority: 3 Importance: Medium X-Mailer: Open-Xchange Mailer v7.8.4-Rev57 X-Originating-Client: open-xchange-appsuite X-Virus-Scanned: ClamAV using ClamSMTP X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mjg59@google.com, dja@axtens.net Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" > On June 3, 2019 at 1:36 AM Andrew Donnellan wrote: > > > On 24/5/19 10:38 pm, Christopher M. Riedl wrote: > > Xmon should be either fully or partially disabled depending on the > > kernel lockdown state. > > > > Put xmon into read-only mode for lockdown=integrity and completely > > disable xmon when lockdown=confidentiality. Xmon checks the lockdown > > state and takes appropriate action: > > > > (1) during xmon_setup to prevent early xmon'ing > > > > (2) when triggered via sysrq > > > > (3) when toggled via debugfs > > > > (4) when triggered via a previously enabled breakpoint > > > > The following lockdown state transitions are handled: > > > > (1) lockdown=none -> lockdown=integrity > > clear all breakpoints, set xmon read-only mode > > > > (2) lockdown=none -> lockdown=confidentiality > > clear all breakpoints, prevent re-entry into xmon > > > > (3) lockdown=integrity -> lockdown=confidentiality > > prevent re-entry into xmon > > > > Suggested-by: Andrew Donnellan > > Signed-off-by: Christopher M. Riedl > > --- > > > > Applies on top of this series: > > https://patchwork.kernel.org/cover/10884631/ > > > > I've done some limited testing of the scenarios mentioned in the commit > > message on a single CPU QEMU config. > > > > v1->v2: > > Fix subject line > > Submit to linuxppc-dev and kernel-hardening > > > > arch/powerpc/xmon/xmon.c | 56 +++++++++++++++++++++++++++++++++++++++- > > 1 file changed, 55 insertions(+), 1 deletion(-) > > > > diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c > > index 3e7be19aa208..8c4a5a0c28f0 100644 > > --- a/arch/powerpc/xmon/xmon.c > > +++ b/arch/powerpc/xmon/xmon.c > > @@ -191,6 +191,9 @@ static void dump_tlb_44x(void); > > static void dump_tlb_book3e(void); > > #endif > > > > +static void clear_all_bpt(void); > > +static void xmon_init(int); > > + > > #ifdef CONFIG_PPC64 > > #define REG "%.16lx" > > #else > > @@ -291,6 +294,39 @@ Commands:\n\ > > zh halt\n" > > ; > > > > +#ifdef CONFIG_LOCK_DOWN_KERNEL > > +static bool xmon_check_lockdown(void) > > +{ > > + static bool lockdown = false; > > + > > + if (!lockdown) { > > + lockdown = kernel_is_locked_down("Using xmon", > > + LOCKDOWN_CONFIDENTIALITY); > > + if (lockdown) { > > + printf("xmon: Disabled by strict kernel lockdown\n"); > > + xmon_on = 0; > > + xmon_init(0); > > + } > > + } > > + > > + if (!xmon_is_ro) { > > + xmon_is_ro = kernel_is_locked_down("Using xmon write-access", > > + LOCKDOWN_INTEGRITY); > > + if (xmon_is_ro) { > > + printf("xmon: Read-only due to kernel lockdown\n"); > > + clear_all_bpt(); > > Remind me again why we need to clear breakpoints in integrity mode? > > > Andrew > I interpreted "integrity" mode as meaning that any changes made by xmon should be reversed. This also covers the case when a user creates some breakpoint(s) in xmon, exits xmon, and then elevates the lockdown state. Upon hitting the first breakpoint and (re-)entering xmon, xmon will clear all breakpoints. Xmon can only take action in response to dynamic lockdown level changes when xmon is invoked in some manner - if there is a better way I am all ears :) > > > + } > > + } > > + > > + return lockdown; > > +} > > +#else > > +inline static bool xmon_check_lockdown(void) > > +{ > > + return false; > > +} > > +#endif /* CONFIG_LOCK_DOWN_KERNEL */ > > + > > static struct pt_regs *xmon_regs; > > > > static inline void sync(void) > > @@ -708,6 +744,9 @@ static int xmon_bpt(struct pt_regs *regs) > > struct bpt *bp; > > unsigned long offset; > > > > + if (xmon_check_lockdown()) > > + return 0; > > + > > if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) > > return 0; > > > > @@ -739,6 +778,9 @@ static int xmon_sstep(struct pt_regs *regs) > > > > static int xmon_break_match(struct pt_regs *regs) > > { > > + if (xmon_check_lockdown()) > > + return 0; > > + > > if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) > > return 0; > > if (dabr.enabled == 0) > > @@ -749,6 +791,9 @@ static int xmon_break_match(struct pt_regs *regs) > > > > static int xmon_iabr_match(struct pt_regs *regs) > > { > > + if (xmon_check_lockdown()) > > + return 0; > > + > > if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) > > return 0; > > if (iabr == NULL) > > @@ -3742,6 +3787,9 @@ static void xmon_init(int enable) > > #ifdef CONFIG_MAGIC_SYSRQ > > static void sysrq_handle_xmon(int key) > > { > > + if (xmon_check_lockdown()) > > + return; > > + > > /* ensure xmon is enabled */ > > xmon_init(1); > > debugger(get_irq_regs()); > > @@ -3763,7 +3811,6 @@ static int __init setup_xmon_sysrq(void) > > device_initcall(setup_xmon_sysrq); > > #endif /* CONFIG_MAGIC_SYSRQ */ > > > > -#ifdef CONFIG_DEBUG_FS > > static void clear_all_bpt(void) > > { > > int i; > > @@ -3785,8 +3832,12 @@ static void clear_all_bpt(void) > > printf("xmon: All breakpoints cleared\n"); > > } > > > > +#ifdef CONFIG_DEBUG_FS > > static int xmon_dbgfs_set(void *data, u64 val) > > { > > + if (xmon_check_lockdown()) > > + return 0; > > + > > xmon_on = !!val; > > xmon_init(xmon_on); > > > > @@ -3845,6 +3896,9 @@ early_param("xmon", early_parse_xmon); > > > > void __init xmon_setup(void) > > { > > + if (xmon_check_lockdown()) > > + return; > > + > > if (xmon_on) > > xmon_init(1); > > if (xmon_early) > > > > -- > Andrew Donnellan OzLabs, ADL Canberra > ajd@linux.ibm.com IBM Australia Limited >