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=-11.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 BA125C43603 for ; Wed, 4 Dec 2019 08:34:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 95E352068E for ; Wed, 4 Dec 2019 08:34:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727501AbfLDIeE (ORCPT ); Wed, 4 Dec 2019 03:34:04 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:56396 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727337AbfLDIdx (ORCPT ); Wed, 4 Dec 2019 03:33:53 -0500 Received: from [5.158.153.53] (helo=tip-bot2.lab.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1icQ6J-0005Fq-GE; Wed, 04 Dec 2019 09:33:35 +0100 Received: from [127.0.1.1] (localhost [IPv6:::1]) by tip-bot2.lab.linutronix.de (Postfix) with ESMTP id 220FB1C2658; Wed, 4 Dec 2019 09:33:35 +0100 (CET) Date: Wed, 04 Dec 2019 08:33:35 -0000 From: "tip-bot2 for Peter Zijlstra" Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: core/kprobes] x86/kprobe: Add comments to arch_{,un}optimize_kprobes() Cc: Alexei Starovoitov , "Steven Rostedt (VMware)" , "Peter Zijlstra (Intel)" , Andy Lutomirski , Borislav Petkov , Brian Gerst , Denys Vlasenko , "H. Peter Anvin" , Linus Torvalds , Thomas Gleixner , Ingo Molnar , x86 , LKML In-Reply-To: <20191111132458.401696663@infradead.org> References: <20191111132458.401696663@infradead.org> MIME-Version: 1.0 Message-ID: <157544841504.21853.14009303480737761897.tip-bot2@tip-bot2> X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the core/kprobes branch of tip: Commit-ID: f2cb4f95b7571f2bebcf226cd92b448fd58950ca Gitweb: https://git.kernel.org/tip/f2cb4f95b7571f2bebcf226cd92b448fd58950ca Author: Peter Zijlstra AuthorDate: Mon, 11 Nov 2019 14:02:10 +01:00 Committer: Ingo Molnar CommitterDate: Wed, 27 Nov 2019 07:44:25 +01:00 x86/kprobe: Add comments to arch_{,un}optimize_kprobes() Add a few words describing how it is safe to overwrite the 4 bytes after a kprobe. In specific it is possible the JMP.d32 required for the optimized kprobe overwrites multiple instructions. Tested-by: Alexei Starovoitov Tested-by: Steven Rostedt (VMware) Signed-off-by: Peter Zijlstra (Intel) Acked-by: Alexei Starovoitov Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: https://lkml.kernel.org/r/20191111132458.401696663@infradead.org Signed-off-by: Ingo Molnar --- arch/x86/kernel/kprobes/opt.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c index 26e0d6c..3f45b5c 100644 --- a/arch/x86/kernel/kprobes/opt.c +++ b/arch/x86/kernel/kprobes/opt.c @@ -414,8 +414,12 @@ err: } /* - * Replace breakpoints (int3) with relative jumps. + * Replace breakpoints (INT3) with relative jumps (JMP.d32). * Caller must call with locking kprobe_mutex and text_mutex. + * + * The caller will have installed a regular kprobe and after that issued + * syncrhonize_rcu_tasks(), this ensures that the instruction(s) that live in + * the 4 bytes after the INT3 are unused and can now be overwritten. */ void arch_optimize_kprobes(struct list_head *oplist) { @@ -441,7 +445,13 @@ void arch_optimize_kprobes(struct list_head *oplist) } } -/* Replace a relative jump with a breakpoint (int3). */ +/* + * Replace a relative jump (JMP.d32) with a breakpoint (INT3). + * + * After that, we can restore the 4 bytes after the INT3 to undo what + * arch_optimize_kprobes() scribbled. This is safe since those bytes will be + * unused once the INT3 lands. + */ void arch_unoptimize_kprobe(struct optimized_kprobe *op) { arch_arm_kprobe(&op->kp);