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 329A5C433F5 for ; Tue, 10 May 2022 14:42:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238203AbiEJOqk (ORCPT ); Tue, 10 May 2022 10:46:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45996 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346228AbiEJOmi (ORCPT ); Tue, 10 May 2022 10:42:38 -0400 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id B95652FF705; Tue, 10 May 2022 07:00:17 -0700 (PDT) Received: from pwmachine.localnet (154.pool92-186-13.dynamic.orange.es [92.186.13.154]) by linux.microsoft.com (Postfix) with ESMTPSA id A601220EC9A5; Tue, 10 May 2022 07:00:14 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com A601220EC9A5 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1652191217; bh=7OCMzdl5ESPExXL11Am5FVLKgSI7cID21CgOvybjxvw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Dw697TJfld1wJuEyRncPW0WOPvcm4zY57brhwUmjrGHkewRFrfiMqsBGnZ/prTdqi pbM5BdXqFufVjQTmQML1+tOBEi7nspAMBWTBvKPPOU6a1HlyhgxFlOytRxcOyFFymZ qsMx9NCPwYHGJ9ObWDm9rY8x7tS7LovUiggj1nwY= From: Francis Laniel To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, linux-trace-devel@vger.kernel.org, Catalin Marinas , Mark Brown , Peter Collingbourne , Mark Rutland , Kees Cook , Daniel Kiss , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v1 1/1] arm64: Forget syscall if different from execve*() Date: Tue, 10 May 2022 15:00:11 +0100 Message-ID: <2826417.e9J7NaK4W3@pwmachine> Organization: Microsoft In-Reply-To: <20220510105948.GB27557@willie-the-truck> References: <20220509151958.441240-1-flaniel@linux.microsoft.com> <20220509151958.441240-2-flaniel@linux.microsoft.com> <20220510105948.GB27557@willie-the-truck> 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-kernel@vger.kernel.org Hi. Le mardi 10 mai 2022, 11:59:48 BST Will Deacon a =E9crit : > On Mon, May 09, 2022 at 04:19:57PM +0100, Francis Laniel wrote: > > This patch enables exeve*() to be traced by syscalls:sys_exit_execve > > tracepoint. > > Previously, calling forget_syscall() would set syscall to -1, which > > impedes > > this tracepoint to prints its information. > > So, this patch makes call to forget_syscall() conditional by only calli= ng > > it when syscall number is not execve() or execveat(). > >=20 > > Signed-off-by: Francis Laniel > > --- > >=20 > > arch/arm64/include/asm/processor.h | 8 +++++++- > > 1 file changed, 7 insertions(+), 1 deletion(-) > >=20 > > diff --git a/arch/arm64/include/asm/processor.h > > b/arch/arm64/include/asm/processor.h index 73e38d9a540c..e12ceb363d6a > > 100644 > > --- a/arch/arm64/include/asm/processor.h > > +++ b/arch/arm64/include/asm/processor.h > > @@ -34,6 +34,8 @@ > >=20 > > #include > >=20 > > +#include > > + > >=20 > > #include > > #include > > #include > >=20 > > @@ -250,8 +252,12 @@ 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); > > + if (previous_syscall =3D=3D __NR_execve || previous_syscall =3D=3D > > __NR_execveat) > > + regs->syscallno =3D previous_syscall; > > + else > > + forget_syscall(regs); >=20 > Hmm, this really looks like a bodge and it doesn't handle the compat case > either. >=20 > How do other architectures handle this? My understanding of others architectures is quite limited, but here are my= =20 findings and understanding of some of them: * arm (32 bits) EABI: start_thread() sets r7 to previous r7 for ELF FDPIC = and=20 to 0 for other binfmts [1]. * arm (32 bits) OABI: syscall number is set to -1 if=20 ptrace_report_syscall_entry() failed [2]. * mips: start_thread() does not modify current_thread_info->syscall which i= s=20 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 conta= in=20 the syscall number [6]. > Will Best regards. =2D-- [1] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/arm/include/asm/ processor.h#L52 [2] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/arm/kernel/ ptrace.c#L847 [3] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/mips/kernel/ process.c#L52 [4] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/mips/kernel/ scall64-n64.S#L85 [5] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/riscv/kernel/ process.c#L87 [6] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/x86/kernel/ process_64.c#L505