From patchwork Wed Jan 30 21:57:15 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Herton Ronaldo Krzesinski X-Patchwork-Id: 217037 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from chlorine.canonical.com (chlorine.canonical.com [91.189.94.204]) by ozlabs.org (Postfix) with ESMTP id 7A6C12C0295 for ; Thu, 31 Jan 2013 10:12:18 +1100 (EST) Received: from localhost ([127.0.0.1] helo=chlorine.canonical.com) by chlorine.canonical.com with esmtp (Exim 4.71) (envelope-from ) id 1U0fek-00004t-Cn; Wed, 30 Jan 2013 21:57:22 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by chlorine.canonical.com with esmtp (Exim 4.71) (envelope-from ) id 1U0feh-0008Ug-Nn for kernel-team@lists.ubuntu.com; Wed, 30 Jan 2013 21:57:19 +0000 Received: from 189.58.14.63.dynamic.adsl.gvt.net.br ([189.58.14.63] helo=canonical.com) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1U0feh-0004rT-1C; Wed, 30 Jan 2013 21:57:19 +0000 From: Herton Ronaldo Krzesinski To: Andrew Cooper Subject: [ 3.5.y.z extended stable ] Patch "xen: Fix stack corruption in xen_failsafe_callback for 32bit" has been added to staging queue Date: Wed, 30 Jan 2013 19:57:15 -0200 Message-Id: <1359583035-17121-1-git-send-email-herton.krzesinski@canonical.com> X-Mailer: git-send-email 1.7.9.5 X-Extended-Stable: 3.5 Cc: Frediano Ziglio , kernel-team@lists.ubuntu.com, Konrad Rzeszutek Wilk X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.13 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: kernel-team-bounces@lists.ubuntu.com Errors-To: kernel-team-bounces@lists.ubuntu.com This is a note to let you know that I have just added a patch titled xen: Fix stack corruption in xen_failsafe_callback for 32bit to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Herton ------ From a013d8f0974128c22e5a89984d9733bd408d6f37 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Wed, 16 Jan 2013 12:00:55 +0000 Subject: [PATCH] xen: Fix stack corruption in xen_failsafe_callback for 32bit PVOPS guests. commit 9174adbee4a9a49d0139f5d71969852b36720809 upstream. This fixes CVE-2013-0190 / XSA-40 There has been an error on the xen_failsafe_callback path for failed iret, which causes the stack pointer to be wrong when entering the iret_exc error path. This can result in the kernel crashing. In the classic kernel case, the relevant code looked a little like: popl %eax # Error code from hypervisor jz 5f addl $16,%esp jmp iret_exc # Hypervisor said iret fault 5: addl $16,%esp # Hypervisor said segment selector fault Here, there are two identical addls on either option of a branch which appears to have been optimised by hoisting it above the jz, and converting it to an lea, which leaves the flags register unaffected. In the PVOPS case, the code looks like: popl_cfi %eax # Error from the hypervisor lea 16(%esp),%esp # Add $16 before choosing fault path CFI_ADJUST_CFA_OFFSET -16 jz 5f addl $16,%esp # Incorrectly adjust %esp again jmp iret_exc It is possible unprivileged userspace applications to cause this behaviour, for example by loading an LDT code selector, then changing the code selector to be not-present. At this point, there is a race condition where it is possible for the hypervisor to return back to userspace from an interrupt, fault on its own iret, and inject a failsafe_callback into the kernel. This bug has been present since the introduction of Xen PVOPS support in commit 5ead97c84 (xen: Core Xen implementation), in 2.6.23. Signed-off-by: Frediano Ziglio Signed-off-by: Andrew Cooper Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Herton Ronaldo Krzesinski --- arch/x86/kernel/entry_32.S | 1 - 1 file changed, 1 deletion(-) -- 1.7.9.5 diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S index 8f8e8ee..2a6919e 100644 --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -1065,7 +1065,6 @@ ENTRY(xen_failsafe_callback) lea 16(%esp),%esp CFI_ADJUST_CFA_OFFSET -16 jz 5f - addl $16,%esp jmp iret_exc 5: pushl_cfi $-1 /* orig_ax = -1 => not a system call */ SAVE_ALL