From patchwork Sat Jul 9 10:57:02 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tixy X-Patchwork-Id: 959142 Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) by demeter2.kernel.org (8.14.4/8.14.4) with ESMTP id p69B6UeG025466 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Sat, 9 Jul 2011 11:06:51 GMT Received: from canuck.infradead.org ([2001:4978:20e::1]) by merlin.infradead.org with esmtps (Exim 4.76 #1 (Red Hat Linux)) id 1QfVKP-0002rM-1S; Sat, 09 Jul 2011 11:04:05 +0000 Received: from localhost ([127.0.0.1] helo=canuck.infradead.org) by canuck.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1QfVKN-00061P-IO; Sat, 09 Jul 2011 11:04:03 +0000 Received: from smarthost02.mail.zen.net.uk ([212.23.3.141]) by canuck.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1QfVEO-0004Ke-Ad for linux-arm-kernel@lists.infradead.org; Sat, 09 Jul 2011 10:58:02 +0000 Received: from [82.69.122.217] (helo=plug1) by smarthost02.mail.zen.net.uk with esmtpsa (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.63) (envelope-from ) id 1QfVEN-0005gx-AB for linux-arm-kernel@lists.infradead.org; Sat, 09 Jul 2011 10:57:51 +0000 Received: from [192.168.2.20] (helo=computer2) by plug1 with esmtp (Exim 4.72) (envelope-from ) id 1QfVEL-0003gu-JU for linux-arm-kernel@lists.infradead.org; Sat, 09 Jul 2011 11:57:49 +0100 Received: from tixy by computer2 with local (Exim 4.72) (envelope-from ) id 1QfVEL-0005To-Eq for linux-arm-kernel@lists.infradead.org; Sat, 09 Jul 2011 11:57:49 +0100 From: Tixy To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 15/51] ARM: kprobes: Don't trigger probes on conditional instructions when condition is false Date: Sat, 9 Jul 2011 11:57:02 +0100 Message-Id: <1310209058-20980-16-git-send-email-tixy@yxit.co.uk> X-Mailer: git-send-email 1.7.2.5 In-Reply-To: <1310209058-20980-1-git-send-email-tixy@yxit.co.uk> References: <1310209058-20980-1-git-send-email-tixy@yxit.co.uk> X-Originating-Smarthost02-IP: [82.69.122.217] X-CRM114-Version: 20090807-BlameThorstenAndJenny ( TRE 0.7.6 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20110709_065752_994807_29ED4473 X-CRM114-Status: GOOD ( 17.75 ) X-Spam-Score: 0.0 (/) X-Spam-Report: SpamAssassin version 3.3.1 on canuck.infradead.org summary: Content analysis details: (0.0 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [212.23.3.141 listed in list.dnswl.org] X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: linux-arm-kernel-bounces@lists.infradead.org Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Greylist: IP, sender and recipient auto-whitelisted, not delayed by milter-greylist-4.2.6 (demeter2.kernel.org [140.211.167.43]); Sat, 09 Jul 2011 11:06:51 +0000 (UTC) From: Jon Medhurst This patch changes the behavior of kprobes on ARM so that: Kprobes on conditional instructions don't trigger when the condition is false. For conditional branches, this means that they don't trigger in the branch not taken case. Rationale: When probes are placed onto conditionally executed instructions in a Thumb IT block, they may not fire if the condition is not met. This is because we use invalid instructions for breakpoints and "it is IMPLEMENTATION DEFINED whether the instruction executes as a NOP or causes an Undefined Instruction exception". Therefore, for consistency, we will ignore all probes on any conditional instructions when the condition is false. Alternative solutions seem to be too complex to implement or inconsistent. This issue was discussed on linux.arm.kernel in the thread titled "[RFC] kprobes with thumb2 conditional code" See http://comments.gmane.org/gmane.linux.linaro.devel/2985 Signed-off-by: Jon Medhurst Acked-by: Nicolas Pitre --- arch/arm/kernel/kprobes.c | 24 +++++++++++++++++++++++- 1 files changed, 23 insertions(+), 1 deletions(-) diff --git a/arch/arm/kernel/kprobes.c b/arch/arm/kernel/kprobes.c index b8f5b3b..7a9be60 100644 --- a/arch/arm/kernel/kprobes.c +++ b/arch/arm/kernel/kprobes.c @@ -207,6 +207,20 @@ static void __kprobes set_current_kprobe(struct kprobe *p) __get_cpu_var(current_kprobe) = p; } +static void __kprobes +singlestep_skip(struct kprobe *p, struct pt_regs *regs) +{ +#ifdef CONFIG_THUMB2_KERNEL + regs->ARM_cpsr = it_advance(regs->ARM_cpsr); + if (is_wide_instruction(p->opcode)) + regs->ARM_pc += 4; + else + regs->ARM_pc += 2; +#else + regs->ARM_pc += 4; +#endif +} + static void __kprobes singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb) { @@ -262,7 +276,8 @@ void __kprobes kprobe_handler(struct pt_regs *regs) /* impossible cases */ BUG(); } - } else { + } else if (p->ainsn.insn_check_cc(regs->ARM_cpsr)) { + /* Probe hit and conditional execution check ok. */ set_current_kprobe(p); kcb->kprobe_status = KPROBE_HIT_ACTIVE; @@ -282,6 +297,13 @@ void __kprobes kprobe_handler(struct pt_regs *regs) } reset_current_kprobe(); } + } else { + /* + * Probe hit but conditional execution check failed, + * so just skip the instruction and continue as if + * nothing had happened. + */ + singlestep_skip(p, regs); } } else if (cur) { /* We probably hit a jprobe. Call its break handler. */