From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754562AbdKALdI (ORCPT ); Wed, 1 Nov 2017 07:33:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:38254 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753474AbdKALdF (ORCPT ); Wed, 1 Nov 2017 07:33:05 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB4CD2191E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org X-Google-Smtp-Source: ABhQp+SWOkfS4ZVRRAU0sGk6LtcnFMJ/+D3gtW7956cWFCGrqHJyQ1gwYiAklpEfn/+G7WsB+ruWmrUOSs5ewnFAK2Q= MIME-Version: 1.0 In-Reply-To: <20171027200447.GA12039@nazgul.tnic> References: <8042a4bd5882599dd8e3f9b17f1f40a2fdda0450.1509006199.git.luto@kernel.org> <20171027200447.GA12039@nazgul.tnic> From: Andy Lutomirski Date: Wed, 1 Nov 2017 04:32:43 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 02/18] x86/asm/64: Split the iret-to-user and iret-to-kernel paths To: Borislav Petkov Cc: Andy Lutomirski , X86 ML , "linux-kernel@vger.kernel.org" , Brian Gerst , Dave Hansen , Linus Torvalds Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 27, 2017 at 1:04 PM, Borislav Petkov wrote: > On Thu, Oct 26, 2017 at 01:26:34AM -0700, Andy Lutomirski wrote: >> These code paths will diverge soon. >> >> Signed-off-by: Andy Lutomirski >> --- >> arch/x86/entry/entry_64.S | 32 +++++++++++++++++++++++--------- >> arch/x86/entry/entry_64_compat.S | 2 +- >> arch/x86/kernel/head_64.S | 2 +- >> 3 files changed, 25 insertions(+), 11 deletions(-) >> >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >> index afe1f403fa0e..493e5e234d36 100644 >> --- a/arch/x86/entry/entry_64.S >> +++ b/arch/x86/entry/entry_64.S >> @@ -321,7 +321,7 @@ syscall_return_via_sysret: >> >> opportunistic_sysret_failed: >> SWAPGS >> - jmp restore_regs_and_iret >> + jmp restore_regs_and_return_to_usermode > > rstor_regs_ret_user > > still sounds pretty ok to me and it is shorter and it is using the > *RSTOR spelling the respective FPU insns use, so should be recognizable. :-) > > And the other one could be > > rstor_regs_ret_kernel > > of course. > >> END(entry_SYSCALL_64) >> >> ENTRY(stub_ptregs_64) >> @@ -423,7 +423,7 @@ ENTRY(ret_from_fork) >> call syscall_return_slowpath /* returns with IRQs disabled */ >> TRACE_IRQS_ON /* user mode is traced as IRQS on */ >> SWAPGS >> - jmp restore_regs_and_iret >> + jmp restore_regs_and_return_to_usermode >> >> 1: >> /* kernel thread */ >> @@ -612,7 +612,19 @@ GLOBAL(retint_user) >> call prepare_exit_to_usermode >> TRACE_IRQS_IRETQ >> SWAPGS >> - jmp restore_regs_and_iret >> + >> +GLOBAL(restore_regs_and_return_to_usermode) >> +#ifdef CONFIG_DEBUG_ENTRY >> + testl $3, CS(%rsp) > > testb > > ditto for the other spot. > >> + jnz 1f >> + ud2 >> +1: >> +#endif > > Why aren't we exploding here unconditionally? I mean, we don't want to > return with RPL != 3 CS for whatever reason... Performance? I'll admit that both of these paths are extremely slow no matter what, but it's nice to get a real dump if we screw it up. I'll leave it as is for v2. Feel free to argue more in v2 :)