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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8977AC32757 for ; Sat, 10 Aug 2019 20:48:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 69B1F208C4 for ; Sat, 10 Aug 2019 20:48:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726365AbfHJUsU (ORCPT ); Sat, 10 Aug 2019 16:48:20 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:54840 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726798AbfHJUoB (ORCPT ); Sat, 10 Aug 2019 16:44:01 -0400 Received: from [192.168.4.242] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1hwYDW-00053s-Qz; Sat, 10 Aug 2019 21:43:58 +0100 Received: from ben by deadeye with local (Exim 4.92) (envelope-from ) id 1hwYDN-0003iS-PJ; Sat, 10 Aug 2019 21:43:49 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, Denis Kirjanov , "Borislav Petkov" , "Andy Lutomirski" , "H. Peter Anvin" , "Peter Zijlstra" , "Linus Torvalds" , "Brian Gerst" , "Denys Vlasenko" , "Ingo Molnar" , "Thomas Gleixner" , "Andy Lutomirski" Date: Sat, 10 Aug 2019 21:40:07 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 122/157] x86/asm/entry/64: Disentangle error_entry/exit gsbase/ebx/usermode code In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.242 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 3.16.72-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Andy Lutomirski commit 539f5113650068ba221197f190267ab727296ef5 upstream. The error_entry/error_exit code to handle gsbase and whether we return to user mdoe was a mess: - error_sti was misnamed. In particular, it did not enable interrupts. - Error handling for gs_change was hopelessly tangled the normal usermode path. Separate it out. This saves a branch in normal entries from kernel mode. - The comments were bad. Fix it up. As a nice side effect, there's now a code path that happens on error entries from user mode. We'll use it soon. Signed-off-by: Andy Lutomirski Cc: Andrew Morton Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/f1be898ab93360169fb845ab85185948832209ee.1433878454.git.luto@kernel.org [ Prettified it, clarified comments some more. ] Signed-off-by: Ingo Molnar [bwh: Backported to 3.16 as dependency of commit 18ec54fdd6d1 "x86/speculation: Prepare entry code for Spectre v1 swapgs mitigations": - We do not use %ebx as a flag since we already have a backport of commit b3681dd548d0 "x86/entry/64: Remove %ebx handling from error_entry/exit", so don't add the comments about that - Adjust filename, context] Signed-off-by: Ben Hutchings --- --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -1446,9 +1446,11 @@ ENTRY(error_entry) SWITCH_KERNEL_CR3 testl $3,CS+8(%rsp) je error_kernelspace -error_swapgs: + + /* We entered from user mode */ SWAPGS -error_sti: + +error_entry_done: TRACE_IRQS_OFF ret @@ -1466,8 +1468,15 @@ error_kernelspace: cmpq %rax,RIP+8(%rsp) je bstep_iret cmpq $gs_change,RIP+8(%rsp) - je error_swapgs - jmp error_sti + jne error_entry_done + + /* + * hack: gs_change can fail with user gsbase. If this happens, fix up + * gsbase and proceed. We'll fix up the exception and land in + * gs_change's error handler with kernel gsbase. + */ + SWAPGS + jmp error_entry_done bstep_iret: /* Fix truncated RIP */ @@ -1475,11 +1484,20 @@ bstep_iret: /* fall through */ error_bad_iret: + /* + * We came from an IRET to user mode, so we have user gsbase. + * Switch to kernel gsbase: + */ SWAPGS + + /* + * Pretend that the exception came from user mode: set up pt_regs + * as if we faulted immediately after IRET. + */ mov %rsp,%rdi call fixup_bad_iret mov %rax,%rsp - jmp error_sti + jmp error_entry_done CFI_ENDPROC END(error_entry)