From patchwork Sat Aug 3 19:00:40 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: 11074557 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 311EC1510 for ; Sat, 3 Aug 2019 18:57:40 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 251852886A for ; Sat, 3 Aug 2019 18:57:40 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1908A28894; Sat, 3 Aug 2019 18:57:40 +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 B38812886A for ; Sat, 3 Aug 2019 18:57:38 +0000 (UTC) Received: (qmail 5148 invoked by uid 550); 3 Aug 2019 18:57:35 -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 Received: (qmail 4092 invoked from network); 3 Aug 2019 18:57:34 -0000 From: "Christopher M. Riedl" To: linuxppc-dev@ozlabs.org, kernel-hardening@lists.openwall.com Cc: dja@axtens.net, mjg59@google.com, Andrew Donnellan Subject: [RFC PATCH v3] powerpc/xmon: Restrict when kernel is locked down Date: Sat, 3 Aug 2019 14:00:40 -0500 Message-Id: <20190803190040.8103-1-cmr@informatik.wtf> X-Mailer: git-send-email 2.22.0 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 set xmon read-only mode (2) lockdown=none -> lockdown=confidentiality clear all breakpoints, set xmon read-only mode, prevent re-entry into xmon (3) lockdown=integrity -> lockdown=confidentiality clear all breakpoints, set xmon read-only mode, prevent re-entry into xmon Suggested-by: Andrew Donnellan Signed-off-by: Christopher M. Riedl --- Changes since v1: - Rebased onto v36 of https://patchwork.kernel.org/cover/11049461/ (based on: f632a8170a6b667ee4e3f552087588f0fe13c4bb) - Do not clear existing breakpoints when transitioning from lockdown=none to lockdown=integrity - Remove line continuation and dangling quote (confuses checkpatch.pl) from the xmon command help/usage string arch/powerpc/xmon/xmon.c | 59 ++++++++++++++++++++++++++++++++++-- include/linux/security.h | 2 ++ security/lockdown/lockdown.c | 2 ++ 3 files changed, 60 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c index d0620d762a5a..1a5e43d664ca 100644 --- a/arch/powerpc/xmon/xmon.c +++ b/arch/powerpc/xmon/xmon.c @@ -25,6 +25,7 @@ #include #include #include +#include #include #include @@ -187,6 +188,9 @@ 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 @@ -283,10 +287,41 @@ Commands:\n\ " U show uptime information\n" " ? help\n" " # n limit output to n lines per page (for dp, dpa, dl)\n" -" zr reboot\n\ - zh halt\n" +" zr reboot\n" +" zh halt\n" ; +#ifdef CONFIG_SECURITY +static bool xmon_is_locked_down(void) +{ + static bool lockdown; + + if (!lockdown) { + lockdown = !!security_locked_down(LOCKDOWN_XMON_RW); + if (lockdown) { + printf("xmon: Disabled due to kernel lockdown\n"); + xmon_is_ro = true; + xmon_on = 0; + xmon_init(0); + clear_all_bpt(); + } + } + + if (!xmon_is_ro) { + xmon_is_ro = !!security_locked_down(LOCKDOWN_XMON_WR); + if (xmon_is_ro) + printf("xmon: Read-only due to kernel lockdown\n"); + } + + return lockdown; +} +#else /* CONFIG_SECURITY */ +static inline bool xmon_is_locked_down(void) +{ + return false; +} +#endif + static struct pt_regs *xmon_regs; static inline void sync(void) @@ -704,6 +739,9 @@ static int xmon_bpt(struct pt_regs *regs) struct bpt *bp; unsigned long offset; + if (xmon_is_locked_down()) + return 0; + if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) return 0; @@ -735,6 +773,9 @@ static int xmon_sstep(struct pt_regs *regs) static int xmon_break_match(struct pt_regs *regs) { + if (xmon_is_locked_down()) + return 0; + if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) return 0; if (dabr.enabled == 0) @@ -745,6 +786,9 @@ static int xmon_break_match(struct pt_regs *regs) static int xmon_iabr_match(struct pt_regs *regs) { + if (xmon_is_locked_down()) + return 0; + if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) return 0; if (iabr == NULL) @@ -3741,6 +3785,9 @@ static void xmon_init(int enable) #ifdef CONFIG_MAGIC_SYSRQ static void sysrq_handle_xmon(int key) { + if (xmon_is_locked_down()) + return; + /* ensure xmon is enabled */ xmon_init(1); debugger(get_irq_regs()); @@ -3762,7 +3809,6 @@ 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; @@ -3784,8 +3830,12 @@ 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_is_locked_down()) + return 0; + xmon_on = !!val; xmon_init(xmon_on); @@ -3844,6 +3894,9 @@ early_param("xmon", early_parse_xmon); void __init xmon_setup(void) { + if (xmon_is_locked_down()) + return; + if (xmon_on) xmon_init(1); if (xmon_early) diff --git a/include/linux/security.h b/include/linux/security.h index 807dc0d24982..379b74b5d545 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -116,12 +116,14 @@ enum lockdown_reason { LOCKDOWN_MODULE_PARAMETERS, LOCKDOWN_MMIOTRACE, LOCKDOWN_DEBUGFS, + LOCKDOWN_XMON_WR, LOCKDOWN_INTEGRITY_MAX, LOCKDOWN_KCORE, LOCKDOWN_KPROBES, LOCKDOWN_BPF_READ, LOCKDOWN_PERF, LOCKDOWN_TRACEFS, + LOCKDOWN_XMON_RW, LOCKDOWN_CONFIDENTIALITY_MAX, }; diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c index f6c74cf6a798..79d1799a62ca 100644 --- a/security/lockdown/lockdown.c +++ b/security/lockdown/lockdown.c @@ -31,12 +31,14 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters", [LOCKDOWN_MMIOTRACE] = "unsafe mmio", [LOCKDOWN_DEBUGFS] = "debugfs access", + [LOCKDOWN_XMON_WR] = "xmon write access", [LOCKDOWN_INTEGRITY_MAX] = "integrity", [LOCKDOWN_KCORE] = "/proc/kcore access", [LOCKDOWN_KPROBES] = "use of kprobes", [LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM", [LOCKDOWN_PERF] = "unsafe use of perf", [LOCKDOWN_TRACEFS] = "use of tracefs", + [LOCKDOWN_XMON_RW] = "xmon read and write access", [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality", };