From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from na01-bl2-obe.outbound.protection.outlook.com (mail-bl2on0123.outbound.protection.outlook.com [65.55.169.123]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 1836B1A084B for ; Wed, 11 Feb 2015 18:59:47 +1100 (AEDT) Message-ID: <54DB0BDD.2010807@freescale.com> Date: Wed, 11 Feb 2015 09:59:25 +0200 From: Purcareata Bogdan MIME-Version: 1.0 To: Michael Ellerman , Bogdan Purcareata Subject: Re: [RFC][PATCH 1/3] powerpc: Don't force ENOSYS as error on syscall fail References: <1423468516-8688-1-git-send-email-bogdan.purcareata@freescale.com> <1423468516-8688-2-git-send-email-bogdan.purcareata@freescale.com> <1423623845.12568.1.camel@ellerman.id.au> In-Reply-To: <1423623845.12568.1.camel@ellerman.id.au> Content-Type: text/plain; charset="utf-8"; format=flowed Cc: linux-kernel@vger.kernel.org, pmoore@redhat.com, paulus@samba.org, strosake@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 11.02.2015 05:04, Michael Ellerman wrote: > On Mon, 2015-02-09 at 07:55 +0000, Bogdan Purcareata wrote: >> In certain scenarios - e.g. seccomp filtering with ERRNO as default action - >> the system call fails for other reasons than the syscall not being available. >> The seccomp filter can be configured to store a user-defined error code on >> return from a blacklisted syscall. >> >> The RFC is this: are there currently any user-space scenarios where it is >> required that the system call return ENOSYS as error code on failure, no matter >> the circumstances? I don't want to break userspace requirements. I have not >> added code to force this error code in situations different than >> secure_computing failure, in order to keep overhead at a minimum. >> >> Signed-off-by: Bogdan Purcareata >> --- >> arch/powerpc/kernel/entry_32.S | 3 ++- >> arch/powerpc/kernel/entry_64.S | 2 +- >> 2 files changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S >> index 59848e5..52e48dd 100644 >> --- a/arch/powerpc/kernel/entry_32.S >> +++ b/arch/powerpc/kernel/entry_32.S >> @@ -425,7 +425,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX) >> b 1b >> #endif /* CONFIG_44x */ >> >> -66: li r3,-ENOSYS >> +66: >> +# li r3,-ENOSYS >> b ret_from_syscall >> >> .globl ret_from_fork >> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S >> index e6bfe8e..80db02e 100644 >> --- a/arch/powerpc/kernel/entry_64.S >> +++ b/arch/powerpc/kernel/entry_64.S >> @@ -269,7 +269,7 @@ syscall_dotrace: >> b .Lsyscall_dotrace_cont >> >> syscall_enosys: >> - li r3,-ENOSYS >> +# li r3,-ENOSYS >> b syscall_exit > > So what happens if you call this with a syscall number that's out of bounds? As far as my current understanding goes, the call will return with -1 with a errno that's undefined (or I've not seen it be defined anywhere). I've thought more about this, and I guess the best option would be to move setting -ENOSYS as errno from the syscall entry assembly to do_syscall_trace_enter (as opposed to eliminating it at all). I was a little reluctant to do this at first in order to keep overhead to a minimum, but it's certainly not an option to change behavior if the syscall number is out of bounds. v2 to come shortly. Thanks, Bogdan P.