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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 332D2C54FCB for ; Wed, 22 Apr 2020 20:08:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 01C0F2074B for ; Wed, 22 Apr 2020 20:08:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="gch71prR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726380AbgDVUIk (ORCPT ); Wed, 22 Apr 2020 16:08:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41964 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726002AbgDVUIj (ORCPT ); Wed, 22 Apr 2020 16:08:39 -0400 Received: from merlin.infradead.org (unknown [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 94F4DC03C1A9 for ; Wed, 22 Apr 2020 13:08:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=MZtG2KeEuTg4yxv86Z8L4utsUbXSvWTuQZuzRxUSn2U=; b=gch71prRJAzB3Y0FYH7ky8mFbA 6RnCv0KWoS5iBsJKg3sBToeckgJV5VR3hoEBm1JHcqArZY70gy9M7qQ3vaYWxbrVUCSD/MofQ7hOJ b/s8jO6kZy8b6bx/EGQdid//orECye8WG/jSblkkoq4sRtcqX/+W6wY3NMXKxWGYL5Sm5sQEK5AXs X2A+xfB5yKKjlVUZd5wgH4rhHpSXkNgrf+Wo4cC+VYopsFS6iIgtgRfTTCBZFKlb0bC52tk6WWYYD w6jy7ZH/jPa1Y5Yxo/pSyNhrA+eVOq8HMGtROIrE0IZzXyXS2enl7WN57KPzegQik+SWuF8gVPW0C I0cwTHDQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jRLfH-0000bq-MX; Wed, 22 Apr 2020 20:08:11 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 8C4169836F8; Wed, 22 Apr 2020 22:08:08 +0200 (CEST) Date: Wed, 22 Apr 2020 22:08:08 +0200 From: Peter Zijlstra To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, jpoimboe@redhat.com, x86@kernel.org, mhiramat@kernel.org, mbenes@suse.cz, jthierry@redhat.com, alexandre.chartre@oracle.com Subject: Re: [PATCH 3/3] x86/ftrace: Do not jump to direct code in created trampolines Message-ID: <20200422200808.GX2483@worktop.programming.kicks-ass.net> References: <20200422162539.808362933@goodmis.org> <20200422162750.638839749@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200422162750.638839749@goodmis.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 22, 2020 at 12:25:42PM -0400, Steven Rostedt wrote: > @@ -367,6 +371,17 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) > if (WARN_ON(ret < 0)) > goto fail; > > + /* No need to test direct calls on created trampolines */ > + if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { > + /* NOP the jnz 1f; but make sure it's a 2 byte jnz */ > + ip = trampoline + (jmp_offset - start_offset); > + if (WARN_ON(*(char *)ip != 0x75)) > + goto fail; > + ret = probe_kernel_read(ip, ideal_nops[2], 2); Now you're just being silly, are you really, actually worried you can't read ideal_nops[] ? > + if (ret < 0) > + goto fail; > + } > + > /* > * The address of the ftrace_ops that is used for this trampoline > * is stored at the end of the trampoline. This will be used to > diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S > index 0882758d165a..f72ef157feb3 100644 > --- a/arch/x86/kernel/ftrace_64.S > +++ b/arch/x86/kernel/ftrace_64.S > @@ -241,6 +241,7 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL) > */ > movq ORIG_RAX(%rsp), %rax > testq %rax, %rax > +SYM_INNER_LABEL(ftrace_regs_caller_jmp, SYM_L_GLOBAL) > jnz 1f > I you worry about performance, it would make more sense to do something like so: SYM_INNER_LABEL(ftrace_regs_caller_from, SYM_L_GLOBAL) movq ORIG_RAX(%rsp), %rax testq %rax, %rax jnz 1f SYM_INNER_LABEL(ftrace_regs_caller_to, SYM_L_GLOBAL) if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { ip = trampoline + (ftrace_regs_caller_from - start_offset); ((u8[])ip)[0] = JMP8_INSN_OPCODE; ((u8[])ip)[1] = ftrace_regs_caller_to - ftrace_regs_caller_from - JMP8_INSN_SIZE; } Or nop the whole range, but it's like 10 bytes so I'm not sure that's actually faster.