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=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 8ED9BC19759 for ; Thu, 1 Aug 2019 14:08:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 64E1B20838 for ; Thu, 1 Aug 2019 14:08:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564668509; bh=IXX2z3LZp9/vh6A4fK4Aj8M5DxOuM9+ZGyNm+tX+k/4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=YAaOWDQhNK1TRRV4FrjVV1AfjDm4Yd1WnbPqtitMCsDlnQ+kLtcgHFlJb3AtayolQ /ch5ClLe7n/tRwWzzSjF/1yKLIsCzIabvb3s7z0o/+e3j8KkadO54SCd1xVFisYl2D /uIncUlw+exiPCntIJsu/pdOOAHqEiXUvWGDGORI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731827AbfHAOI1 (ORCPT ); Thu, 1 Aug 2019 10:08:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:38854 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731814AbfHAOIZ (ORCPT ); Thu, 1 Aug 2019 10:08:25 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A220720679; Thu, 1 Aug 2019 14:08:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564668504; bh=IXX2z3LZp9/vh6A4fK4Aj8M5DxOuM9+ZGyNm+tX+k/4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=pm+No2ALbNs9D3JreUMGhHDgHvV3biwf7mnRH8qzi9I1RVHSjqyh5YskaCxmu8kYo NCLqpdwJ/Ba06p49XKSvpMUCc85N3f4O02ZpbUBh0Ijkk1TNIti22T7W1c9YS+Ctyb cvO99qd1mQuHyQFpT6gORgPt9mR4kon+2lKfkQss= Date: Thu, 1 Aug 2019 23:08:18 +0900 From: Masami Hiramatsu To: Will Deacon Cc: Catalin Marinas , Will Deacon , Dan Rue , Daniel Diaz , Anders Roxell , Naresh Kamboju , linux-kernel@vger.kernel.org, James Morse , Matt Hart , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v3 1/4] arm64: kprobes: Recover pstate.D in single-step exception handler Message-Id: <20190801230818.72fadeea8a58d1f657179b30@kernel.org> In-Reply-To: <20190801121622.vs57a6e2syklyr3z@willie-the-truck> References: <156404254387.2020.886452004489353899.stgit@devnote2> <156404255444.2020.3301023170351823334.stgit@devnote2> <20190801121622.vs57a6e2syklyr3z@willie-the-truck> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 1 Aug 2019 13:16:22 +0100 Will Deacon wrote: > On Thu, Jul 25, 2019 at 05:15:54PM +0900, Masami Hiramatsu wrote: > > kprobes manipulates the interrupted PSTATE for single step, and > > doesn't restore it. Thus, if we put a kprobe where the pstate.D > > (debug) masked, the mask will be cleared after the kprobe hits. > > > > Moreover, in the most complicated case, this can lead a kernel > > crash with below message when a nested kprobe hits. > > > > [ 152.118921] Unexpected kernel single-step exception at EL1 > > > > When the 1st kprobe hits, do_debug_exception() will be called. > > At this point, debug exception (= pstate.D) must be masked (=1). > > But if another kprobes hits before single-step of the first kprobe > > (e.g. inside user pre_handler), it unmask the debug exception > > (pstate.D = 0) and return. > > Then, when the 1st kprobe setting up single-step, it saves current > > DAIF, mask DAIF, enable single-step, and restore DAIF. > > However, since "D" flag in DAIF is cleared by the 2nd kprobe, the > > single-step exception happens soon after restoring DAIF. > > > > This has been introduced by commit 7419333fa15e ("arm64: kprobe: > > Always clear pstate.D in breakpoint exception handler") > > > > To solve this issue, this stores all DAIF bits and restore it > > after single stepping. > > > > Reported-by: Naresh Kamboju > > Fixes: commit 7419333fa15e ("arm64: kprobe: Always clear pstate.D in breakpoint exception handler") > > Reviewed-by: James Morse > > Tested-by: James Morse > > Signed-off-by: Masami Hiramatsu > > --- > > Changes in v3: > > - Update patch description > > - move PSR_DAIF_MASK in daifflags.h > > Changes in v2: > > - Save and restore all DAIF flags. > > - Operate pstate directly and remove spsr_set_debug_flag(). > > --- > > arch/arm64/include/asm/daifflags.h | 2 ++ > > arch/arm64/kernel/probes/kprobes.c | 39 +++++------------------------------- > > 2 files changed, 7 insertions(+), 34 deletions(-) > > I'm seeing an allmodconfig build failure with this: > > arch/arm64/kernel/probes/kprobes.c: In function ‘kprobes_save_local_irqflag’: > arch/arm64/kernel/probes/kprobes.c:181:38: error: ‘DAIF_MASK’ undeclared (first use in this function); did you mean ‘BIT_MASK’? > kcb->saved_irqflag = regs->pstate & DAIF_MASK; > ^~~~~~~~~ > BIT_MASK > arch/arm64/kernel/probes/kprobes.c:181:38: note: each undeclared identifier is reported only once for each function it appears in > arch/arm64/kernel/probes/kprobes.c: In function ‘kprobes_restore_local_irqflag’: > arch/arm64/kernel/probes/kprobes.c:190:19: error: ‘DAIF_MASK’ undeclared (first use in this function); did you mean ‘BIT_MASK’? > regs->pstate &= ~DAIF_MASK; > ^~~~~~~~~ > BIT_MASK > make[2]: *** [scripts/Makefile.build:274: arch/arm64/kernel/probes/kprobes.o] Error 1 Oops, daifflags.h is included via kvm_host.h... OK, kprobes.c must include daifflags.h directly in this case. I'll update this patch too. Thank you, > > Will -- Masami Hiramatsu