From nobody Sun Feb 8 23:27:17 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 AD9A9C6FD1D for ; Mon, 20 Mar 2023 16:49:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232597AbjCTQtK (ORCPT ); Mon, 20 Mar 2023 12:49:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45986 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232528AbjCTQrm (ORCPT ); Mon, 20 Mar 2023 12:47:42 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 60E9DB766; Mon, 20 Mar 2023 09:41:13 -0700 (PDT) Date: Mon, 20 Mar 2023 16:39:24 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1679330365; 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=UGS0er2Lg/HFrgzNy0+KpO36GJYrn4O60MmTJDzTSbU=; b=3lSYdwOD9gsPSn9Km2sBLy196tHSOp8DfMCbxRqQ/3puZwoYPnvINgzeiudUIY26VHDsM7 q8cJNRaZkbh/B+4/LRTr06ibkW5y4nzCNCKbBnXhDJVK+5hUSHPCIncPTaZ/3r9oXp4kAI ogrVProc2JV1cWL63SFswplN8YadCios0svsoSZMC1SW1moihc3tI4HSU1iuhw2CWNb9BV OVmfiaUhlbRjKKMpUZ8WVvzDreFOJLOfw4QxLNbn9z7iQW4InpcYZU7uw81/xeKRB9hssq 7rP4ccALImzkJ2PMVib2Mz4Y6iL64gvjYJ2VNJupjOfcx3lhCNIid5rsdzJAwA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1679330365; 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=UGS0er2Lg/HFrgzNy0+KpO36GJYrn4O60MmTJDzTSbU=; b=R8J+Ljfqrv9YhI7Dc6tEXTIJuz3YvzMCPyMF7zhmvXYFb9dbW0X2KlCcCNARVD3FcVho52 tZZ948lnqBt+qLAA== 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: <167933036476.5837.3311348958638945300.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: 75818f575af6d20c96ac42fd8fc59020ed24f331 Gitweb: https://git.kernel.org/tip/75818f575af6d20c96ac42fd8fc59020e= d24f331 Author: Rick Edgecombe AuthorDate: Sat, 18 Mar 2023 17:15:19 -07:00 Committer: Dave Hansen CommitterDate: Mon, 20 Mar 2023 09:01:10 -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. 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/20230319001535.23210-25-rick.p.edgecombe%= 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 d81e7ec..2e3d8cc 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -1638,6 +1638,11 @@ 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 eab18ba..e7c7bcc 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -978,7 +978,7 @@ static int check_vma_flags(struct vm_area_struct *vma, = unsigned long gup_flags) return -EFAULT; =20 if (write) { - 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. */