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=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable 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 84866C43218 for ; Thu, 25 Apr 2019 16:26:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DF68120891 for ; Thu, 25 Apr 2019 16:26:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="VqnasD/z" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730114AbfDYQ0i (ORCPT ); Thu, 25 Apr 2019 12:26:38 -0400 Received: from mail.skyhub.de ([5.9.137.197]:55772 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729906AbfDYQ03 (ORCPT ); Thu, 25 Apr 2019 12:26:29 -0400 Received: from zn.tnic (p200300EC2F0E43001D86563D61B131D5.dip0.t-ipconnect.de [IPv6:2003:ec:2f0e:4300:1d86:563d:61b1:31d5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 9F9F91EC050B; Thu, 25 Apr 2019 18:26:27 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1556209587; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=bhEpDc5d4HyhQ2bpVjieSeCZ31GaRinPp/sR5VeHQ6U=; b=VqnasD/zMdS+0uAelD4hutyqDB8IyeLbKILtFiZqFO8GVwKD8qzxgPpJi0rWWAzqt3XCkv 0lhbY7oIEM/5nlBPWCr1Oc92xyJvS3bMpMsjBKLeFHZBxLgMAduzCX4bZ+Rz0S2WdHmSYZ PHMxLE/J/50mz0+wo+W3eQrFC84hXuc= Date: Thu, 25 Apr 2019 18:26:21 +0200 From: Borislav Petkov To: Rick Edgecombe Cc: Andy Lutomirski , Ingo Molnar , linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com, Thomas Gleixner , 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 Subject: Re: [PATCH v4 03/23] x86/mm: Introduce temporary mm structs Message-ID: <20190425162620.GA5199@zn.tnic> References: <20190422185805.1169-1-rick.p.edgecombe@intel.com> <20190422185805.1169-4-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190422185805.1169-4-rick.p.edgecombe@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 22, 2019 at 11:57:45AM -0700, Rick Edgecombe wrote: > 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..d684b954f3c0 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 *prev; > +} temp_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 s/cores/CPUs/g Yeah, the concept of a thread of execution we call a CPU in the kernel, I'd say. No matter if it is one of the hyperthreads or a single thread in core. > + * 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. Ditto. > Using temporary mm also allows to avoid TLB shootdowns when the Using a .. > + * mapping is torn down. > + * Nice commenting. > + * 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 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(temp_mm_state_t prev) > +{ > + lockdep_assert_irqs_disabled(); > + switch_mm_irqs_off(NULL, prev.prev, current); I think this code would be more readable if you call that temp_mm_state_t variable "temp_state" and the mm_struct pointer "mm" and then you have: switch_mm_irqs_off(NULL, temp_state.mm, current); And above you'll have: temp_state.mm = ... Thx. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.