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=-16.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 8A752C433E0 for ; Wed, 24 Mar 2021 22:58:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E38A61A1E for ; Wed, 24 Mar 2021 22:58:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234462AbhCXW5j (ORCPT ); Wed, 24 Mar 2021 18:57:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:57222 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234060AbhCXW46 (ORCPT ); Wed, 24 Mar 2021 18:56:58 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 985FD61993; Wed, 24 Mar 2021 22:56:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1616626618; bh=kEx0BBmKM5vaHGCI5rYHxg4ywAbd7vl646tPmmLEfRY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=bZwM/78Mv9hzqhfR+oUIJVGdlq2Q5Uc6a5djcP64DwUPJAOo6Z4nxTFl5ZrQLir4s q8o+9CKjWTyM4CqnuFamt/9qXzNVhvdfaZsRQ7qJlhhY2PGmH2EmP/eWNor0zAgCzl DPSEl7sJP4/d+ZSF5bd17w1t/nDGJlhXkWXIy91DgHZqiKuMOUA66+UL9YjlByDwO/ rhU5JNhUET2b9VtUvRqg3s4P/pPPjwEMx1Ud2e0QNHHQO78PmaUkspWfC33O1i/kjK 5p2dPksGb6wdzrFJeu4bC/5C/ciTCkp0GBaL4ZAAgM7IE9zMON8bwHcJI5dDKNN5kk LRCl9sWXVgbWw== Date: Thu, 25 Mar 2021 07:56:54 +0900 From: Masami Hiramatsu To: Colin Ian King Cc: Muhammad Usama Anjum , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , "Peter Zijlstra (Intel)" , linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org, dan.carpenter@oracle.com Subject: Re: [PATCH] x86/kprobes: Remove dead code Message-Id: <20210325075654.98e4a89c1ce5d25f47b87b78@kernel.org> In-Reply-To: <5fcd5b04-0fab-3672-c5d2-6e8f73f93bbc@canonical.com> References: <20210324173641.GA404706@LEGION> <5fcd5b04-0fab-3672-c5d2-6e8f73f93bbc@canonical.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 24 Mar 2021 17:50:16 +0000 Colin Ian King wrote: > On 24/03/2021 17:36, Muhammad Usama Anjum wrote: > > The condition in switch statement `opcode & 0xf0` cannot evaluate to > > 0xff. So this case statement will never execute. Remove it. > > > > Fixes: 6256e668b7 ("x86/kprobes: Use int3 instead of debug trap for single-step") > > Signed-off-by: Muhammad Usama Anjum > > --- > > arch/x86/kernel/kprobes/core.c | 3 --- > > 1 file changed, 3 deletions(-) > > > > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c > > index 89d9f26785c7..3b7bcc077020 100644 > > --- a/arch/x86/kernel/kprobes/core.c > > +++ b/arch/x86/kernel/kprobes/core.c > > @@ -177,9 +177,6 @@ int can_boost(struct insn *insn, void *addr) > > case 0xf0: > > /* clear and set flags are boostable */ > > return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe)); > > - case 0xff: > > - /* indirect jmp is boostable */ > > - return X86_MODRM_REG(insn->modrm.bytes[0]) == 4; > > default: > > /* CS override prefix and call are not boostable */ > > return (opcode != 0x2e && opcode != 0x9a); > > > > The 0xff case was added with some form of intention to be executed so I > suspect removing it is not an appropriate fix. Right, it must be moved under the case 0xf0. Something like this. case 0xf0: if (opcde == 0xff) { /* indirect jmp is boostable */ return X86_MODRM_REG(insn->modrm.bytes[0]) == 4; } Thank you, -- Masami Hiramatsu