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=-2.6 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 B68E8C5CFEB for ; Wed, 11 Jul 2018 11:30:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6887F208FA for ; Wed, 11 Jul 2018 11:30:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=8bytes.org header.i=@8bytes.org header.b="TrzgZZic" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6887F208FA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=8bytes.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733157AbeGKLef (ORCPT ); Wed, 11 Jul 2018 07:34:35 -0400 Received: from 8bytes.org ([81.169.241.247]:37770 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733075AbeGKLeR (ORCPT ); Wed, 11 Jul 2018 07:34:17 -0400 Received: by theia.8bytes.org (Postfix, from userid 1000) id 77477309F; Wed, 11 Jul 2018 13:30:07 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=8bytes.org; s=mail-1; t=1531308608; bh=rH3pHIAZjes8fXXsCzld/lB2OED0lZmhYxZj0vhyKjY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TrzgZZicvprPxn1HhyaJ6THvUmeXEwlpjtZXrnHUXNdXvOi4BwNEcj/YCvCoIQLM3 Se268MmgdEwEEF3X4a63RRS1cZ2pLB4Bp2rJNh0y+iO4vYs8PwZkFqo7wZJAT9fTTV uP0GRnFoare5G1eWva9jlHbA0hsuR1ySuhmsIktJFYcpmSm+K3uuu2Tkj2TWnfdOa2 Nk2k3qavzkYkGvSRiwmXkqytTrrCTHA+SkCPYtGcEhNU5Fans95qvYDDdJqaPKS1SX yiwCTTKxb503p7kx8niI3iaSPYoFsBRT4eFUmexly0jVudt9SaKha2qLUN28KFifmt 90ANZ7QZ2BR8g== From: Joerg Roedel To: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Andy Lutomirski , Dave Hansen , Josh Poimboeuf , Juergen Gross , Peter Zijlstra , Borislav Petkov , Jiri Kosina , Boris Ostrovsky , Brian Gerst , David Laight , Denys Vlasenko , Eduardo Valentin , Greg KH , Will Deacon , aliguori@amazon.com, daniel.gruss@iaik.tugraz.at, hughd@google.com, keescook@google.com, Andrea Arcangeli , Waiman Long , Pavel Machek , "David H . Gutteridge" , jroedel@suse.de, joro@8bytes.org Subject: [PATCH 39/39] x86/entry/32: Add debug code to check entry/exit cr3 Date: Wed, 11 Jul 2018 13:29:46 +0200 Message-Id: <1531308586-29340-40-git-send-email-joro@8bytes.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1531308586-29340-1-git-send-email-joro@8bytes.org> References: <1531308586-29340-1-git-send-email-joro@8bytes.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Joerg Roedel Add a config option that enabled code to check that we enter and leave the kernel with the correct cr3. This is needed because we have no NX protection of user-addresses in the kernel-cr3 on x86-32 and wouldn't notice that type of bug otherwise. Signed-off-by: Joerg Roedel --- arch/x86/Kconfig.debug | 12 ++++++++++++ arch/x86/entry/entry_32.S | 43 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 55 insertions(+) diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index c6dd1d9..6eaca2d 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -340,6 +340,18 @@ config X86_DEBUG_FPU If unsure, say N. +config X86_DEBUG_ENTRY_CR3 + bool "Debug CR3 for Kernel entry/exit" + depends on X86_32 && PAGE_TABLE_ISOLATION + help + Add instructions to the x86-32 entry code to check whether the kernel + is entered and left with the correct CR3. When PTI is enabled, this + checks whether we enter the kernel with the user-space cr3 when + coming from user-mode and if we leave with user-cr3 back to + user-space. + + If unsure, say N. + config PUNIT_ATOM_DEBUG tristate "ATOM Punit debug driver" depends on PCI diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index a368583..d8d9a54 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -166,6 +166,24 @@ .Lend_\@: .endm +.macro BUG_IF_WRONG_CR3 no_user_check=0 +#ifdef CONFIG_X86_DEBUG_ENTRY_CR3 + ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI + .if \no_user_check == 0 + /* coming from usermode? */ + testl $SEGMENT_RPL_MASK, PT_CS(%esp) + jz .Lend_\@ + .endif + /* On user-cr3? */ + movl %cr3, %eax + testl $PTI_SWITCH_MASK, %eax + jnz .Lend_\@ + /* From userspace with kernel cr3 - BUG */ + ud2 +.Lend_\@: +#endif +.endm + /* * Switch to kernel cr3 if not already loaded and return current cr3 in * \scratch_reg @@ -218,6 +236,8 @@ .macro SAVE_ALL_NMI cr3_reg:req SAVE_ALL + BUG_IF_WRONG_CR3 + /* * Now switch the CR3 when PTI is enabled. * @@ -229,6 +249,7 @@ .Lend_\@: .endm + /* * This is a sneaky trick to help the unwinder find pt_regs on the stack. The * frame pointer is replaced with an encoded pointer to pt_regs. The encoding @@ -292,6 +313,8 @@ .Lswitched_\@: + BUG_IF_WRONG_CR3 + RESTORE_REGS pop=\pop .endm @@ -362,6 +385,8 @@ ALTERNATIVE "", "jmp .Lend_\@", X86_FEATURE_XENPV + BUG_IF_WRONG_CR3 + SWITCH_TO_KERNEL_CR3 scratch_reg=%eax /* @@ -803,6 +828,7 @@ ENTRY(entry_SYSENTER_32) */ pushfl pushl %eax + BUG_IF_WRONG_CR3 no_user_check=1 SWITCH_TO_KERNEL_CR3 scratch_reg=%eax popl %eax popfl @@ -897,6 +923,7 @@ ENTRY(entry_SYSENTER_32) * whereas POPF does not.) */ btrl $X86_EFLAGS_IF_BIT, (%esp) + BUG_IF_WRONG_CR3 no_user_check=1 popfl popl %eax @@ -974,6 +1001,8 @@ restore_all: /* Switch back to user CR3 */ SWITCH_TO_USER_CR3 scratch_reg=%eax + BUG_IF_WRONG_CR3 + /* Restore user state */ RESTORE_REGS pop=4 # skip orig_eax/error_code .Lirq_return: @@ -987,6 +1016,7 @@ restore_all: restore_all_kernel: TRACE_IRQS_IRET PARANOID_EXIT_TO_KERNEL_MODE + BUG_IF_WRONG_CR3 RESTORE_REGS 4 jmp .Lirq_return @@ -994,6 +1024,19 @@ restore_all_kernel: ENTRY(iret_exc ) pushl $0 # no error code pushl $do_iret_error + +#ifdef CONFIG_X86_DEBUG_ENTRY_CR3 + /* + * The stack-frame here is the one that iret faulted on, so its a + * return-to-user frame. We are on kernel-cr3 because we come here from + * the fixup code. This confuses the CR3 checker, so switch to user-cr3 + * as the checker expects it. + */ + pushl %eax + SWITCH_TO_USER_CR3 scratch_reg=%eax + popl %eax +#endif + jmp common_exception .previous _ASM_EXTABLE(.Lirq_return, iret_exc) -- 2.7.4