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: 10959825 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 14B01112C for ; Fri, 24 May 2019 13:03:11 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 02FE72885E for ; Fri, 24 May 2019 13:03:11 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id EAF4D28867; Fri, 24 May 2019 13:03:10 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id 09D4E2885E for ; Fri, 24 May 2019 13:03:09 +0000 (UTC) Received: (qmail 19586 invoked by uid 550); 24 May 2019 13:03:08 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Delivered-To: moderator for kernel-hardening@lists.openwall.com Received: (qmail 26379 invoked from network); 24 May 2019 12:37:29 -0000 From: "Christopher M. Riedl" To: linuxppc-dev@ozlabs.org, kernel-hardening@lists.openwall.com Cc: ajd@linux.ibm.com, mjg59@google.com, dja@axtens.net, "Christopher M. Riedl" 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-Virus-Scanned: ClamAV using ClamSMTP 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)