From nobody Sun Feb 8 09:12:11 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76AD7C001DF for ; Wed, 2 Aug 2023 22:21:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230156AbjHBWVO (ORCPT ); Wed, 2 Aug 2023 18:21:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33196 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234015AbjHBWUg (ORCPT ); Wed, 2 Aug 2023 18:20:36 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4D3FD30E8; Wed, 2 Aug 2023 15:19:42 -0700 (PDT) Date: Wed, 02 Aug 2023 22:19:39 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1691014780; h=from:from:sender:sender:reply-to: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:content-transfer-encoding; bh=f5xr0qqhwkFwmGDZ3sWJHT7R0N1dk0BNM0pyytXy6ps=; b=NQwOo5YpqyQBbLcHo9otywP04dPs2NqzrldOeCDI2fndWCkOG/oRUHF7AS9mL4s+IN6WNb nKXZPRZHXj1GKGP8nLeWzKFiT6kmImXFzg8YQ++AAEtBdh6d7X9bWdzoo8c3WL5xupQRb1 dSYmLM5ZNsj+8+U/cpgkhnllX+uHISmLrs5KqBnpN9lO9FQYICzS5hElyy1mdulxooU0NV kHKcikXBTcTP3BfdrJUvUNMlbz3dUCmVP66bYTSfyHBKTTyiOcpUBbGIeCt6R6G/NMacL6 6M2rxqtNMbCdlF+v+kOiL85fMj804N0OWcJwcu1Gs64C7RJvdCNOJMZ0Fyb8IQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1691014780; h=from:from:sender:sender:reply-to: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:content-transfer-encoding; bh=f5xr0qqhwkFwmGDZ3sWJHT7R0N1dk0BNM0pyytXy6ps=; b=oTZuHZfL/Uq/ND3gGcykJATVnEmeG+vkUkNAX6QE9Ip2xsQLdmrO2dz9HqXNQl6ObKfihT yf+UVBih7eQnzfCg== From: "tip-bot2 for Rick Edgecombe" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/shstk] mm: Don't allow write GUPs to shadow stack memory Cc: Rick Edgecombe , Dave Hansen , "Borislav Petkov (AMD)" , Kees Cook , "Mike Rapoport (IBM)" , David Hildenbrand , Pengfei Xu , John Allen , x86@kernel.org, linux-kernel@vger.kernel.org MIME-Version: 1.0 Message-ID: <169101477945.28540.8558037470123487928.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the x86/shstk branch of tip: Commit-ID: 6beb99580bc040aed1d5fe7ed9083a4be77f3c20 Gitweb: https://git.kernel.org/tip/6beb99580bc040aed1d5fe7ed9083a4be= 77f3c20 Author: Rick Edgecombe AuthorDate: Mon, 12 Jun 2023 17:10:48 -07:00 Committer: Dave Hansen CommitterDate: Wed, 02 Aug 2023 15:01:20 -07:00 mm: Don't allow write GUPs to shadow stack memory The x86 Control-flow Enforcement Technology (CET) feature includes a new type of memory called shadow stack. This shadow stack memory has some unusual properties, which requires some core mm changes to function properly. In userspace, shadow stack memory is writable only in very specific, controlled ways. However, since userspace can, even in the limited ways, modify shadow stack contents, the kernel treats it as writable memory. As a result, without additional work there would remain many ways for userspace to trigger the kernel to write arbitrary data to shadow stacks via get_user_pages(, FOLL_WRITE) based operations. To help userspace protect their shadow stacks, make this a little less exposed by blocking writable get_user_pages() operations for shadow stack VMAs. Still allow FOLL_FORCE to write through shadow stack protections, as it does for read-only protections. This is required for debugging use cases. [ dhansen: fix rebase goof, readd writable_file_mapping_allowed() hunk ] Signed-off-by: Rick Edgecombe Signed-off-by: Dave Hansen Reviewed-by: Borislav Petkov (AMD) Reviewed-by: Kees Cook Acked-by: Mike Rapoport (IBM) Acked-by: David Hildenbrand Tested-by: Pengfei Xu Tested-by: John Allen Tested-by: Kees Cook Link: https://lore.kernel.org/all/20230613001108.3040476-23-rick.p.edgecomb= e%40intel.com --- arch/x86/include/asm/pgtable.h | 5 +++++ mm/gup.c | 2 +- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index 61b5244..e95cfd3 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -1631,6 +1631,11 @@ static inline bool __pte_access_permitted(unsigned l= ong pteval, bool write) { unsigned long need_pte_bits =3D _PAGE_PRESENT|_PAGE_USER; =20 + /* + * Write=3D0,Dirty=3D1 PTEs are shadow stack, which the kernel + * shouldn't generally allow access to, but since they + * are already Write=3D0, the below logic covers both cases. + */ if (write) need_pte_bits |=3D _PAGE_RW; =20 diff --git a/mm/gup.c b/mm/gup.c index 76d222c..44c2658 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1054,7 +1054,7 @@ static int check_vma_flags(struct vm_area_struct *vma= , unsigned long gup_flags) !writable_file_mapping_allowed(vma, gup_flags)) return -EFAULT; =20 - if (!(vm_flags & VM_WRITE)) { + if (!(vm_flags & VM_WRITE) || (vm_flags & VM_SHADOW_STACK)) { if (!(gup_flags & FOLL_FORCE)) return -EFAULT; /* hugetlb does not support FOLL_FORCE|FOLL_WRITE. */