From patchwork Fri May 24 12:38:18 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Christopher M. Riedl" X-Patchwork-Id: 1104888 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 459Qs838wKz9s1c for ; Fri, 24 May 2019 22:38:36 +1000 (AEST) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=informatik.wtf Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 459Qs8217NzDqWN for ; Fri, 24 May 2019 22:38:36 +1000 (AEST) X-Original-To: linuxppc-dev@lists.ozlabs.org Delivered-To: linuxppc-dev@lists.ozlabs.org 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)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 459Qqn0BrbzDqRS for ; Fri, 24 May 2019 22:37:25 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=informatik.wtf Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) by bilbo.ozlabs.org (Postfix) with ESMTP id 459Qqm4zcPz8tFN for ; Fri, 24 May 2019 22:37:24 +1000 (AEST) Received: by ozlabs.org (Postfix) id 459Qqm4Vf1z9s7h; Fri, 24 May 2019 22:37:24 +1000 (AEST) Delivered-To: linuxppc-dev@ozlabs.org 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 459Qql2lncz9s1c for ; Fri, 24 May 2019 22:37:20 +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 8557C6036A; Fri, 24 May 2019 12:37:16 +0000 (UTC) Received: from MTA-06.privateemail.com (localhost [127.0.0.1]) by MTA-06.privateemail.com (Postfix) with ESMTP id 6E1036003D; Fri, 24 May 2019 08:37:16 -0400 (EDT) Received: from wrwlf0000.attlocal.net (unknown [10.20.151.201]) by MTA-06.privateemail.com (Postfix) with ESMTPA id B1D0D60045; Fri, 24 May 2019 12:37:15 +0000 (UTC) From: "Christopher M. Riedl" To: linuxppc-dev@ozlabs.org, kernel-hardening@lists.openwall.com Subject: [RFC PATCH v2] powerpc/xmon: restrict when kernel is locked down Date: Fri, 24 May 2019 07:38:18 -0500 Message-Id: <20190524123816.1773-1-cmr@informatik.wtf> X-Mailer: git-send-email 2.21.0 MIME-Version: 1.0 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: "Christopher M. Riedl" , ajd@linux.ibm.com, mjg59@google.com, dja@axtens.net Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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(); + } + } + + 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)