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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C1D2FC433FE for ; Wed, 18 May 2022 13:34:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=lk9JdBlbEX3UsW1bcCCbctqPPcCQZbvaRdxX605/ibc=; b=E9K3osSzHe6TVZ weyxOnTq2VYiFcj4dNC9bAV20MSgBqAQZkRHxO/ym5lq+4L0mnEzKV8Wv+tjvzoRNQ3AJiWQctkFP qTvMQL1H4sxvh0eLl3QCClGY3DykOmu5GOK/jf0OAzft6gWIFFqscz/se7aMfBGXIZKfXsORkhlF6 jzudkOpBRvmpgFRd0rPafMgda7/26JheTEGOqoqV8y+gcAAJhoD462YGKpOg9K+cTdVK+sIlaYfYB Lg47/+AewfbcnMxMziWCpLWRwo+afDVMVqGOG+4ynUkOK62vbOqFdxhva0S9qS3UkxXlkF1S3LZRG 8Q4awqsfW2JxS7kPq5XQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nrJna-002KBo-FA; Wed, 18 May 2022 13:33:10 +0000 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nrJnW-002KAy-7c for linux-arm-kernel@lists.infradead.org; Wed, 18 May 2022 13:33:08 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 27FEEB82079; Wed, 18 May 2022 13:33:03 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C57CDC385A5; Wed, 18 May 2022 13:32:59 +0000 (UTC) Date: Wed, 18 May 2022 14:32:56 +0100 From: Catalin Marinas To: Will Deacon Cc: Francis Laniel , linux-arm-kernel@lists.infradead.org, linux-trace-devel@vger.kernel.org, Mark Brown , Peter Collingbourne , Mark Rutland , Kees Cook , Daniel Kiss , linux-kernel@vger.kernel.org, James Morse Subject: Re: [RFC PATCH v1 1/1] arm64: Forget syscall if different from execve*() Message-ID: References: <20220509151958.441240-1-flaniel@linux.microsoft.com> <20220509151958.441240-2-flaniel@linux.microsoft.com> <20220510105948.GB27557@willie-the-truck> <2826417.e9J7NaK4W3@pwmachine> <20220510140333.GA28104@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220510140333.GA28104@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220518_063306_588894_745ECDFD X-CRM114-Status: GOOD ( 28.18 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, May 10, 2022 at 03:03:33PM +0100, Will Deacon wrote: > On Tue, May 10, 2022 at 03:00:11PM +0100, Francis Laniel wrote: > > Le mardi 10 mai 2022, 11:59:48 BST Will Deacon a =EF=BF=BDcrit : > > > On Mon, May 09, 2022 at 04:19:57PM +0100, Francis Laniel wrote: > > > > diff --git a/arch/arm64/include/asm/processor.h > > > > b/arch/arm64/include/asm/processor.h index 73e38d9a540c..e12ceb363d= 6a > > > > 100644 > > > > --- a/arch/arm64/include/asm/processor.h > > > > +++ b/arch/arm64/include/asm/processor.h > > > > @@ -34,6 +34,8 @@ > > > > = > > > > #include > > > > = > > > > +#include > > > > + > > > > = > > > > #include > > > > #include > > > > #include > > > > = > > > > @@ -250,8 +252,12 @@ void tls_preserve_current_state(void); > > > > = > > > > static inline void start_thread_common(struct pt_regs *regs, unsig= ned > > > > long pc) { > > > > = > > > > + s32 previous_syscall =3D regs->syscallno; > > > > = > > > > memset(regs, 0, sizeof(*regs)); > > > > = > > > > - forget_syscall(regs); > > > > + if (previous_syscall =3D=3D __NR_execve || previous_syscall =3D= =3D > > > > __NR_execveat) > > > > + regs->syscallno =3D previous_syscall; > > > > + else > > > > + forget_syscall(regs); > > > = > > > Hmm, this really looks like a bodge and it doesn't handle the compat = case > > > either. > > > = > > > How do other architectures handle this? > > = > > My understanding of others architectures is quite limited, but here are= my = > > findings and understanding of some of them: > > * arm (32 bits) EABI: start_thread() sets r7 to previous r7 for ELF FDP= IC and = > > to 0 for other binfmts [1]. > > * arm (32 bits) OABI: syscall number is set to -1 if = > > ptrace_report_syscall_entry() failed [2]. > > * mips: start_thread() does not modify current_thread_info->syscall whi= ch is = > > taken directly from v0 [3, 4]. > > * riscv: start_thread() does not modify a7 [5]. > > * x86_64: start_thread_common() does not touch orig_ax which seems to c= ontain = > > the syscall number [6]. > = > Hmm, so the million dollar question is why on Earth we have that > forget_syscall() call to start with. Amusingly I've, err, forgotten; > forget_forget_syscall() perhaps? > = > Catalin? It's been there since day one afaict. Looking at the old logs, this appeared somewhere between day 0 and 1. We had a memset(regs, 0) with a pt_regs of 36 registers but moved to dedicated names for syscallno etc. and that's where I changed it from 0 to ~0UL. A few weeks ago James Morse (cc'ed) came across this issue and even sent a patch internally to remove forget_syscall() here. But that looks like a bodge and James' suggestion was that maybe the core code can preserve the syscallno and this would fix it for all architectures. -- = Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel