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=-7.9 required=3.0 tests=DATE_IN_PAST_06_12, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,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 6E035C43218 for ; Fri, 26 Apr 2019 07:31:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4CBD12089E for ; Fri, 26 Apr 2019 07:31:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726124AbfDZHbt (ORCPT ); Fri, 26 Apr 2019 03:31:49 -0400 Received: from ex13-edg-ou-002.vmware.com ([208.91.0.190]:29121 "EHLO EX13-EDG-OU-002.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725912AbfDZHbr (ORCPT ); Fri, 26 Apr 2019 03:31:47 -0400 Received: from sc9-mailhost3.vmware.com (10.113.161.73) by EX13-EDG-OU-002.vmware.com (10.113.208.156) with Microsoft SMTP Server id 15.0.1156.6; Fri, 26 Apr 2019 00:31:44 -0700 Received: from sc2-haas01-esx0118.eng.vmware.com (sc2-haas01-esx0118.eng.vmware.com [10.172.44.118]) by sc9-mailhost3.vmware.com (Postfix) with ESMTP id 77C0D412A1; Fri, 26 Apr 2019 00:31:45 -0700 (PDT) From: Nadav Amit To: Peter Zijlstra , Borislav Petkov , Andy Lutomirski , Ingo Molnar CC: , , , Thomas Gleixner , Nadav Amit , Dave Hansen , , , , , , , , , , , Rick Edgecombe , Kees Cook , Dave Hansen , Nadav Amit Subject: [PATCH v5 03/23] x86/mm: Introduce temporary mm structs Date: Thu, 25 Apr 2019 17:11:23 -0700 Message-ID: <20190426001143.4983-4-namit@vmware.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190426001143.4983-1-namit@vmware.com> References: <20190426001143.4983-1-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: None (EX13-EDG-OU-002.vmware.com: namit@vmware.com does not designate permitted sender hosts) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: From: Andy Lutomirski Using a dedicated page-table for temporary PTEs prevents other cores from using - even speculatively - these PTEs, thereby providing two benefits: (1) Security hardening: an attacker that gains kernel memory writing abilities cannot easily overwrite sensitive data. (2) Avoiding TLB shootdowns: the PTEs do not need to be flushed in remote page-tables. To do so a temporary mm_struct can be used. Mappings which are private for this mm can be set in the userspace part of the address-space. During the whole time in which the temporary mm is loaded, interrupts must be disabled. The first use-case for temporary mm struct, which will follow, is for poking the kernel text. [ Commit message was written by Nadav Amit ] Cc: Kees Cook Cc: Dave Hansen Acked-by: Peter Zijlstra (Intel) Reviewed-by: Masami Hiramatsu Tested-by: Masami Hiramatsu Signed-off-by: Andy Lutomirski Signed-off-by: Nadav Amit Signed-off-by: Rick Edgecombe --- arch/x86/include/asm/mmu_context.h | 33 ++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 19d18fae6ec6..24dc3b810970 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -356,4 +356,37 @@ static inline unsigned long __get_current_cr3_fast(void) return cr3; } +typedef struct { + struct mm_struct *mm; +} temp_mm_state_t; + +/* + * Using a temporary mm allows to set temporary mappings that are not accessible + * by other CPUs. Such mappings are needed to perform sensitive memory writes + * that override the kernel memory protections (e.g., W^X), without exposing the + * temporary page-table mappings that are required for these write operations to + * other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the + * mapping is torn down. + * + * Context: The temporary mm needs to be used exclusively by a single core. To + * harden security IRQs must be disabled while the temporary mm is + * loaded, thereby preventing interrupt handler bugs from overriding + * the kernel memory protection. + */ +static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) +{ + temp_mm_state_t temp_state; + + lockdep_assert_irqs_disabled(); + temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm); + switch_mm_irqs_off(NULL, mm, current); + return temp_state; +} + +static inline void unuse_temporary_mm(temp_mm_state_t prev_state) +{ + lockdep_assert_irqs_disabled(); + switch_mm_irqs_off(NULL, prev_state.mm, current); +} + #endif /* _ASM_X86_MMU_CONTEXT_H */ -- 2.17.1