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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 79C5EC433EF for ; Fri, 1 Jul 2022 11:36:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235022AbiGALgr (ORCPT ); Fri, 1 Jul 2022 07:36:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37858 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234207AbiGALgl (ORCPT ); Fri, 1 Jul 2022 07:36:41 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CD80D814AE; Fri, 1 Jul 2022 04:36:40 -0700 (PDT) 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 8F7CDB80813; Fri, 1 Jul 2022 11:36:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D8F63C3411E; Fri, 1 Jul 2022 11:36:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1656675398; bh=ht0/icXtp2sEhQfzOe1RuBtF1QGRO0mLy1F9NHIwIJo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qyZWqqP3YjsMKExY+ED0ZanHiTPDFeMdcC/nLGmH+vSBWrYqBQh8SxDCTc5Q21gLf Lv5facBuIZ1jWgWiHzMjhxV4Occp1skkxdu6vo21XEI1H/F53M6Ye4LgopehyHWt49 htVQPCblbBFrPs9L7ob86ybN7B2z263YOm5+d3cq+yTRVCh0+rvTSDCHjwePEH5+wo XEndL5gBSwwkmwkIWxSXidRDERgwEVE4V96JMjZ6g0aIzNE1k2HqV4wEZsAVbitjak PC9dlRbm/nJ44eKV1THZwK+9YC2Sx7dSYUGjsd2DMCBAEuX9rSalrKbr+HGGdzg/1b A5IWpBj0QR6GA== Date: Fri, 1 Jul 2022 12:36:32 +0100 From: Will Deacon To: Francis Laniel Cc: linux-trace-devel@vger.kernel.org, James Morse , Daniel Kiss , Catalin Marinas , Mark Brown , Peter Collingbourne , Kees Cook , Mark Rutland , Christophe Leroy , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/1] arm64: Do not forget syscall when starting a new thread. Message-ID: <20220701113631.GC28070@willie-the-truck> References: <20220608162447.666494-1-flaniel@linux.microsoft.com> <20220628135834.GA24116@willie-the-truck> <3439466.iIbC2pHGDl@pwmachine> <4722000.GXAFRqVoOG@pwmachine> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4722000.GXAFRqVoOG@pwmachine> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 30, 2022 at 07:16:44PM +0200, Francis Laniel wrote: > Hi. > > Le mardi 28 juin 2022, 21:26:32 CEST Francis Laniel a écrit : > > Hi. > > > > Le mardi 28 juin 2022, 15:58:35 CEST Will Deacon a écrit : > > > On Wed, Jun 08, 2022 at 05:24:46PM +0100, Francis Laniel wrote: > > > > This patch enables exeve*() to be traced with syscalls:sys_exit_execve > > > > tracepoint. > > > > Previous to it, by calling forget_syscall(), this tracepoint would not > > > > print its information as syscall is -1. > > > > So, this patch removes call to forget_syscall() and set regs->syscallno > > > > to its previous value. > > > > > > > > Signed-off-by: Francis Laniel > > > > --- > > > > > > > > arch/arm64/include/asm/processor.h | 3 ++- > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/arch/arm64/include/asm/processor.h > > > > b/arch/arm64/include/asm/processor.h index 9e58749db21d..86eb0bfe3b38 > > > > 100644 > > > > --- a/arch/arm64/include/asm/processor.h > > > > +++ b/arch/arm64/include/asm/processor.h > > > > @@ -272,8 +272,9 @@ void tls_preserve_current_state(void); > > > > > > > > static inline void start_thread_common(struct pt_regs *regs, unsigned > > > > long pc) { > > > > > > > > + s32 previous_syscall = regs->syscallno; > > > > > > > > memset(regs, 0, sizeof(*regs)); > > > > > > > > - forget_syscall(regs); > > > > + regs->syscallno = previous_syscall; > > > > > > I'm still unsure about this. Even if we preserve the syscall number here, > > > won't all the arguments be reported as 0? > > > > I am not really sure what you meant about arguments, can you please precise > > between command line arguments (ls -al) and syscall arguments (argp, envp, > > etc.)? > > Indeed, if my understanding is correct syscall arguments are showed by > > sys_enter_* while sys_exit_* only reports the syscall return code. > > > > Regarding the return code I think the value is correct as it is used in > > syscall_trace_exit() but set in invoke_syscall() after the syscall finishes > > [1, 2]. > > The comparison of arm64 and amd64 output also shows no difference: > > # amd64 > > ls 435739 [002] 24689.292479: syscalls:sys_exit_execve: 0x0 > > 7fc43732e100 _start+0x0 (/usr/lib/x86_64-linux-gnu/ld-2.31.so) > > # arm64 > > ls 266 [000] 34.708444: syscalls:sys_exit_execve: 0x0 > > 1140 [unknown] (/usr/lib/aarch64-linux-gnu/ld-2.31.so) > > > > > I also looked quickly at the 32-bit arch/arm/ code and it looks like the > > > same behaviour exists there (module CONFIG_BINFMT_ELF_FDPIC). > > > > I tested arm32 and it is not affected (even though I did not have > CONFIG_BINFMT_ELF_FDPIC set). > Here is ftrace output for arm64 without this patch: > bash-316 [000] ..... 72.167342: sys_execve(filename: > aaaaf9bbcd30, argv: aaaaf9bb54f0, envp: aaaaf9a7d9b0) > Here is the output for arm64 with this patch: > cat-313 [000] ..... 417.926073: sys_execve(filename: > aaaaee7ce9f0, argv: aaaaee7833a0, envp: aaaaee6a69b0) > cat-313 [000] ..... 417.939619: sys_execve -> 0x0 > And here is output for arm32: > cat-254 [000] ..... 127.804128: sys_execve(filename: 5bff18, > argv: 53bb00, envp: 5543a8) > cat-254 [000] ..... 127.809142: sys_execve -> 0x0 > From the above, the arm32 output seems correct even though: > # CONFIG_BINFMT_ELF_FDPIC is not set > > After some debugging, I realized that arm32 syscall_get_nr() uses abi_syscall > to get the syscall number and not a register (I guess abi_syscall was set to > value of R7 before) [1]. > So the fact that regs->uregs are memset'ed to 0 is not a problem. Thanks for confirming this, I'll go ahead and queue your patch and let's hope nothing breaks :) Will