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 C761FC433EF for ; Thu, 30 Jun 2022 17:16:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236000AbiF3RQw (ORCPT ); Thu, 30 Jun 2022 13:16:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42894 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235518AbiF3RQv (ORCPT ); Thu, 30 Jun 2022 13:16:51 -0400 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9BEE33E5CB; Thu, 30 Jun 2022 10:16:49 -0700 (PDT) Received: from pwmachine.localnet (lfbn-lyo-1-1062-211.w86-248.abo.wanadoo.fr [86.248.131.211]) by linux.microsoft.com (Postfix) with ESMTPSA id 2DC9820CD162; Thu, 30 Jun 2022 10:16:47 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 2DC9820CD162 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1656609409; bh=SGD2plOXYG2nU4Of126mBupBbHA9hW8xg+IkPu4iDNg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AQbqXMoUrJxHzROhBQ3e0SJezOdTvWLczgzgy2+lK/lGe5/pJ6Y2A5KoLCbB3m0jD 1/N/By54UqMsk6HuD3ClVbUpctFpbDBksdZAr3VSC0H5jQM1bJlOZwjblrRgnxuSQK c/zxz6wjAU3lhtoHlQqeb5JBAIrIbOQUMwRagtJU= From: Francis Laniel To: Will Deacon 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. Date: Thu, 30 Jun 2022 19:16:44 +0200 Message-ID: <4722000.GXAFRqVoOG@pwmachine> Organization: Microsoft In-Reply-To: <3439466.iIbC2pHGDl@pwmachine> References: <20220608162447.666494-1-flaniel@linux.microsoft.com> <20220628135834.GA24116@willie-the-truck> <3439466.iIbC2pHGDl@pwmachine> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1" Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org Hi. Le mardi 28 juin 2022, 21:26:32 CEST Francis Laniel a =E9crit : > Hi. >=20 > Le mardi 28 juin 2022, 15:58:35 CEST Will Deacon a =E9crit : > > 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->syscall= no > > > to its previous value. > > >=20 > > > Signed-off-by: Francis Laniel > > > --- > > >=20 > > > arch/arm64/include/asm/processor.h | 3 ++- > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > >=20 > > > 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); > > >=20 > > > static inline void start_thread_common(struct pt_regs *regs, unsigned > > > long pc) { > > >=20 > > > + s32 previous_syscall =3D regs->syscallno; > > >=20 > > > memset(regs, 0, sizeof(*regs)); > > >=20 > > > - forget_syscall(regs); > > > + regs->syscallno =3D previous_syscall; > >=20 > > I'm still unsure about this. Even if we preserve the syscall number her= e, > > won't all the arguments be reported as 0? >=20 > I am not really sure what you meant about arguments, can you please preci= se > 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. >=20 > 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 finish= es > [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) >=20 > > 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). >=20 I tested arm32 and it is not affected (even though I did not have=20 CONFIG_BINFMT_ELF_FDPIC set). Here is ftrace output for arm64 without this patch: bash-316 [000] ..... 72.167342: sys_execve(filename:=20 aaaaf9bbcd30, argv: aaaaf9bb54f0, envp: aaaaf9a7d9b0) Here is the output for arm64 with this patch: cat-313 [000] ..... 417.926073: sys_execve(filename:=20 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: 5bf= f18,=20 argv: 53bb00, envp: 5543a8) cat-254 [000] ..... 127.809142: sys_execve -> 0x0 =46rom 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_sysca= ll=20 to get the syscall number and not a register (I guess abi_syscall was set t= o=20 value of R7 before) [1]. So the fact that regs->uregs are memset'ed to 0 is not a problem. >=20 > Best regards. > --- > [1] https://elixir.bootlin.com/linux/v5.18/source/arch/arm64/kernel/ > ptrace.c#L1868 > [2] https://elixir.bootlin.com/linux/v5.18/source/arch/arm64/kernel/ > syscall.c#L57 Best regards. =2D-- [1] https://elixir.bootlin.com/linux/v5.18.8/source/arch/arm/include/asm/ syscall.h#L22