From patchwork Thu Jan 17 00:32:45 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Rick Edgecombe X-Patchwork-Id: 10767295 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2275314E5 for ; Thu, 17 Jan 2019 00:34:41 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E02D12DE41 for ; Thu, 17 Jan 2019 00:34:33 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id D34042E297; Thu, 17 Jan 2019 00:34:33 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id E7B392E1E1 for ; Thu, 17 Jan 2019 00:34:32 +0000 (UTC) Received: (qmail 1262 invoked by uid 550); 17 Jan 2019 00:33:53 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 1103 invoked from network); 17 Jan 2019 00:33:52 -0000 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,488,1539673200"; d="scan'208";a="292166015" From: Rick Edgecombe To: Andy Lutomirski , Ingo Molnar Cc: linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com, Thomas Gleixner , Borislav Petkov , Nadav Amit , Dave Hansen , Peter Zijlstra , linux_dti@icloud.com, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, akpm@linux-foundation.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, will.deacon@arm.com, ard.biesheuvel@linaro.org, kristen@linux.intel.com, deneen.t.dock@intel.com, Kees Cook , Dave Hansen , Nadav Amit , Rick Edgecombe Subject: [PATCH 03/17] x86/mm: temporary mm struct Date: Wed, 16 Jan 2019 16:32:45 -0800 Message-Id: <20190117003259.23141-4-rick.p.edgecombe@intel.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190117003259.23141-1-rick.p.edgecombe@intel.com> References: <20190117003259.23141-1-rick.p.edgecombe@intel.com> X-Virus-Scanned: ClamAV using ClamSMTP From: Andy Lutomirski Sometimes we want to set a temporary page-table entries (PTEs) in one of the cores, without allowing other cores to use - even speculatively - these mappings. There are two benefits for doing so: (1) Security: if sensitive PTEs are set, temporary mm prevents their use in other cores. This hardens the security as it prevents exploding a dangling pointer to overwrite sensitive data using the sensitive PTE. (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 PTEs, which will follow, is for poking the kernel text. [ Commit message was written by Nadav ] Cc: Kees Cook Cc: Peter Zijlstra Cc: Dave Hansen 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 | 32 ++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 0ca50611e8ce..0141b7fa6d01 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -338,4 +338,36 @@ static inline unsigned long __get_current_cr3_fast(void) return cr3; } +typedef struct { + struct mm_struct *prev; +} temporary_mm_state_t; + +/* + * Using a temporary mm allows to set temporary mappings that are not accessible + * by other cores. 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 cores. + * + * 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 override the + * kernel memory protection. + */ +static inline temporary_mm_state_t use_temporary_mm(struct mm_struct *mm) +{ + temporary_mm_state_t state; + + lockdep_assert_irqs_disabled(); + state.prev = this_cpu_read(cpu_tlbstate.loaded_mm); + switch_mm_irqs_off(NULL, mm, current); + return state; +} + +static inline void unuse_temporary_mm(temporary_mm_state_t prev) +{ + lockdep_assert_irqs_disabled(); + switch_mm_irqs_off(NULL, prev.prev, current); +} + #endif /* _ASM_X86_MMU_CONTEXT_H */