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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 9BC57ECDE5F for ; Thu, 19 Jul 2018 23:24:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 50B6C20673 for ; Thu, 19 Jul 2018 23:24:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 50B6C20673 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zytor.com 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 S1731147AbeGTAJ5 (ORCPT ); Thu, 19 Jul 2018 20:09:57 -0400 Received: from terminus.zytor.com ([198.137.202.136]:46283 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727556AbeGTAJ5 (ORCPT ); Thu, 19 Jul 2018 20:09:57 -0400 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id w6JNNZkT2451390 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Thu, 19 Jul 2018 16:23:35 -0700 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id w6JNNZtE2451387; Thu, 19 Jul 2018 16:23:35 -0700 Date: Thu, 19 Jul 2018 16:23:35 -0700 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Joerg Roedel Message-ID: Cc: luto@kernel.org, dave.hansen@intel.com, aarcange@redhat.com, llong@redhat.com, peterz@infradead.org, eduval@amazon.com, brgerst@gmail.com, mingo@kernel.org, tglx@linutronix.de, dvlasenk@redhat.com, linux-kernel@vger.kernel.org, jroedel@suse.de, bp@alien8.de, dhgutteridge@sympatico.ca, David.Laight@aculab.com, jkosina@suse.cz, pavel@ucw.cz, torvalds@linux-foundation.org, gregkh@linuxfoundation.org, boris.ostrovsky@oracle.com, will.deacon@arm.com, jpoimboe@redhat.com, hpa@zytor.com, jgross@suse.com Reply-To: jkosina@suse.cz, David.Laight@aculab.com, dhgutteridge@sympatico.ca, jgross@suse.com, hpa@zytor.com, jpoimboe@redhat.com, will.deacon@arm.com, boris.ostrovsky@oracle.com, gregkh@linuxfoundation.org, torvalds@linux-foundation.org, pavel@ucw.cz, dvlasenk@redhat.com, tglx@linutronix.de, mingo@kernel.org, brgerst@gmail.com, eduval@amazon.com, peterz@infradead.org, aarcange@redhat.com, llong@redhat.com, dave.hansen@intel.com, luto@kernel.org, jroedel@suse.de, bp@alien8.de, linux-kernel@vger.kernel.org In-Reply-To: <1531906876-13451-11-git-send-email-joro@8bytes.org> References: <1531906876-13451-11-git-send-email-joro@8bytes.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/pti] x86/entry/32: Handle Entry from Kernel-Mode on Entry-Stack Git-Commit-ID: b92a165df17ee6e616e43107730f06bf6ecf5d8d 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: b92a165df17ee6e616e43107730f06bf6ecf5d8d Gitweb: https://git.kernel.org/tip/b92a165df17ee6e616e43107730f06bf6ecf5d8d Author: Joerg Roedel AuthorDate: Wed, 18 Jul 2018 11:40:47 +0200 Committer: Thomas Gleixner CommitDate: Fri, 20 Jul 2018 01:11:38 +0200 x86/entry/32: Handle Entry from Kernel-Mode on Entry-Stack It is possible that the kernel is entered from kernel-mode and on the entry-stack. The most common way this happens is when an exception is triggered while loading the user-space segment registers on the kernel-to-userspace exit path. The segment loading needs to be done after the entry-stack switch, because the stack-switch needs kernel %fs for per_cpu access. When this happens, make sure to leave the kernel with the entry-stack again, so that the interrupted code-path runs on the right stack when switching to the user-cr3. Detect this condition on kernel-entry by checking CS.RPL and %esp, and if it happens, copy over the complete content of the entry stack to the task-stack. This needs to be done because once the exception handler is entereed, the task might be scheduled out or even migrated to a different CPU, so this cannot rely on the entry-stack contents. Leave a marker in the stack-frame to detect this condition on the exit path. On the exit path the copy is reversed, copy all of the remaining task-stack back to the entry-stack and switch to it. Signed-off-by: Joerg Roedel Signed-off-by: Thomas Gleixner Tested-by: Pavel Machek Cc: "H . Peter Anvin" Cc: linux-mm@kvack.org Cc: Linus Torvalds Cc: Andy Lutomirski Cc: Dave Hansen Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Peter Zijlstra Cc: Borislav Petkov Cc: Jiri Kosina Cc: Boris Ostrovsky Cc: Brian Gerst Cc: David Laight Cc: Denys Vlasenko Cc: Eduardo Valentin Cc: Greg KH Cc: Will Deacon Cc: aliguori@amazon.com Cc: daniel.gruss@iaik.tugraz.at Cc: hughd@google.com Cc: keescook@google.com Cc: Andrea Arcangeli Cc: Waiman Long Cc: "David H . Gutteridge" Cc: joro@8bytes.org Link: https://lkml.kernel.org/r/1531906876-13451-11-git-send-email-joro@8bytes.org --- arch/x86/entry/entry_32.S | 116 +++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 115 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 763592596727..9d6eceba0461 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -294,6 +294,9 @@ * copied there. So allocate the stack-frame on the task-stack and * switch to it before we do any copying. */ + +#define CS_FROM_ENTRY_STACK (1 << 31) + .macro SWITCH_TO_KERNEL_STACK ALTERNATIVE "", "jmp .Lend_\@", X86_FEATURE_XENPV @@ -316,6 +319,16 @@ /* Load top of task-stack into %edi */ movl TSS_entry2task_stack(%edi), %edi + /* + * Clear unused upper bits of the dword containing the word-sized CS + * slot in pt_regs in case hardware didn't clear it for us. + */ + andl $(0x0000ffff), PT_CS(%esp) + + /* Special case - entry from kernel mode via entry stack */ + testl $SEGMENT_RPL_MASK, PT_CS(%esp) + jz .Lentry_from_kernel_\@ + /* Bytes to copy */ movl $PTREGS_SIZE, %ecx @@ -329,8 +342,8 @@ */ addl $(4 * 4), %ecx -.Lcopy_pt_regs_\@: #endif +.Lcopy_pt_regs_\@: /* Allocate frame on task-stack */ subl %ecx, %edi @@ -346,6 +359,56 @@ cld rep movsl + jmp .Lend_\@ + +.Lentry_from_kernel_\@: + + /* + * This handles the case when we enter the kernel from + * kernel-mode and %esp points to the entry-stack. When this + * happens we need to switch to the task-stack to run C code, + * but switch back to the entry-stack again when we approach + * iret and return to the interrupted code-path. This usually + * happens when we hit an exception while restoring user-space + * segment registers on the way back to user-space. + * + * When we switch to the task-stack here, we can't trust the + * contents of the entry-stack anymore, as the exception handler + * might be scheduled out or moved to another CPU. Therefore we + * copy the complete entry-stack to the task-stack and set a + * marker in the iret-frame (bit 31 of the CS dword) to detect + * what we've done on the iret path. + * + * On the iret path we copy everything back and switch to the + * entry-stack, so that the interrupted kernel code-path + * continues on the same stack it was interrupted with. + * + * Be aware that an NMI can happen anytime in this code. + * + * %esi: Entry-Stack pointer (same as %esp) + * %edi: Top of the task stack + */ + + /* Calculate number of bytes on the entry stack in %ecx */ + movl %esi, %ecx + + /* %ecx to the top of entry-stack */ + andl $(MASK_entry_stack), %ecx + addl $(SIZEOF_entry_stack), %ecx + + /* Number of bytes on the entry stack to %ecx */ + sub %esi, %ecx + + /* Mark stackframe as coming from entry stack */ + orl $CS_FROM_ENTRY_STACK, PT_CS(%esp) + + /* + * %esi and %edi are unchanged, %ecx contains the number of + * bytes to copy. The code at .Lcopy_pt_regs_\@ will allocate + * the stack-frame on task-stack and copy everything over + */ + jmp .Lcopy_pt_regs_\@ + .Lend_\@: .endm @@ -403,6 +466,56 @@ .Lend_\@: .endm +/* + * This macro handles the case when we return to kernel-mode on the iret + * path and have to switch back to the entry stack. + * + * See the comments below the .Lentry_from_kernel_\@ label in the + * SWITCH_TO_KERNEL_STACK macro for more details. + */ +.macro PARANOID_EXIT_TO_KERNEL_MODE + + /* + * Test if we entered the kernel with the entry-stack. Most + * likely we did not, because this code only runs on the + * return-to-kernel path. + */ + testl $CS_FROM_ENTRY_STACK, PT_CS(%esp) + jz .Lend_\@ + + /* Unlikely slow-path */ + + /* Clear marker from stack-frame */ + andl $(~CS_FROM_ENTRY_STACK), PT_CS(%esp) + + /* Copy the remaining task-stack contents to entry-stack */ + movl %esp, %esi + movl PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %edi + + /* Bytes on the task-stack to ecx */ + movl PER_CPU_VAR(cpu_tss_rw + TSS_sp1), %ecx + subl %esi, %ecx + + /* Allocate stack-frame on entry-stack */ + subl %ecx, %edi + + /* + * Save future stack-pointer, we must not switch until the + * copy is done, otherwise the NMI handler could destroy the + * contents of the task-stack we are about to copy. + */ + movl %edi, %ebx + + /* Do the copy */ + shrl $2, %ecx + cld + rep movsl + + /* Safe to switch to entry-stack now */ + movl %ebx, %esp + +.Lend_\@: +.endm /* * %eax: prev task * %edx: next task @@ -764,6 +877,7 @@ restore_all: restore_all_kernel: TRACE_IRQS_IRET + PARANOID_EXIT_TO_KERNEL_MODE RESTORE_REGS 4 jmp .Lirq_return