From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752732AbdHOIw7 (ORCPT ); Tue, 15 Aug 2017 04:52:59 -0400 Received: from terminus.zytor.com ([65.50.211.136]:54163 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752545AbdHOIw5 (ORCPT ); Tue, 15 Aug 2017 04:52:57 -0400 Date: Tue, 15 Aug 2017 01:46:29 -0700 From: tip-bot for Andy Lutomirski Message-ID: Cc: luto@kernel.org, bp@alien8.de, jgross@suse.com, mingo@kernel.org, boris.ostrovsky@oracle.com, andrew.cooper3@citrix.com, peterz@infradead.org, tglx@linutronix.de, torvalds@linux-foundation.org, brgerst@gmail.com, linux-kernel@vger.kernel.org, hpa@zytor.com Reply-To: luto@kernel.org, bp@alien8.de, jgross@suse.com, mingo@kernel.org, tglx@linutronix.de, peterz@infradead.org, andrew.cooper3@citrix.com, boris.ostrovsky@oracle.com, linux-kernel@vger.kernel.org, hpa@zytor.com, brgerst@gmail.com, torvalds@linux-foundation.org In-Reply-To: References: To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/asm] x86/xen/64: Fix the reported SS and CS in SYSCALL Git-Commit-ID: fa2016a8e7d846b306e431646d250500e1da0c33 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: fa2016a8e7d846b306e431646d250500e1da0c33 Gitweb: http://git.kernel.org/tip/fa2016a8e7d846b306e431646d250500e1da0c33 Author: Andy Lutomirski AuthorDate: Mon, 14 Aug 2017 22:36:19 -0700 Committer: Ingo Molnar CommitDate: Tue, 15 Aug 2017 10:10:58 +0200 x86/xen/64: Fix the reported SS and CS in SYSCALL When I cleaned up the Xen SYSCALL entries, I inadvertently changed the reported segment registers. Before my patch, regs->ss was __USER(32)_DS and regs->cs was __USER(32)_CS. After the patch, they are FLAT_USER_CS/DS(32). This had a couple unfortunate effects. It confused the opportunistic fast return logic. It also significantly increased the risk of triggering a nasty glibc bug: https://sourceware.org/bugzilla/show_bug.cgi?id=21269 Update the Xen entry code to change it back. Reported-by: Brian Gerst Signed-off-by: Andy Lutomirski Cc: Andrew Cooper Cc: Boris Ostrovsky Cc: Borislav Petkov Cc: Juergen Gross Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: xen-devel@lists.xenproject.org Fixes: 8a9949bc71a7 ("x86/xen/64: Rearrange the SYSCALL entries") Link: http://lkml.kernel.org/r/daba8351ea2764bb30272296ab9ce08a81bd8264.1502775273.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/xen/xen-asm_64.S | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S index a8a4f4c..c5fee26 100644 --- a/arch/x86/xen/xen-asm_64.S +++ b/arch/x86/xen/xen-asm_64.S @@ -88,6 +88,15 @@ RELOC(xen_sysret64, 1b+1) ENTRY(xen_syscall_target) popq %rcx popq %r11 + + /* + * Neither Xen nor the kernel really knows what the old SS and + * CS were. The kernel expects __USER_DS and __USER_CS, so + * report those values even though Xen will guess its own values. + */ + movq $__USER_DS, 4*8(%rsp) + movq $__USER_CS, 1*8(%rsp) + jmp entry_SYSCALL_64_after_hwframe ENDPROC(xen_syscall_target) @@ -97,6 +106,15 @@ ENDPROC(xen_syscall_target) ENTRY(xen_syscall32_target) popq %rcx popq %r11 + + /* + * Neither Xen nor the kernel really knows what the old SS and + * CS were. The kernel expects __USER32_DS and __USER32_CS, so + * report those values even though Xen will guess its own values. + */ + movq $__USER32_DS, 4*8(%rsp) + movq $__USER32_CS, 1*8(%rsp) + jmp entry_SYSCALL_compat_after_hwframe ENDPROC(xen_syscall32_target)