Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967264AbeAOMvi (ORCPT + 1 other); Mon, 15 Jan 2018 07:51:38 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:51632 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967243AbeAOMva (ORCPT ); Mon, 15 Jan 2018 07:51:30 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dave Hansen , Thomas Gleixner , Andrea Arcangeli , Jon Masters , "Tim Chen" , gnomes@lxorguk.ukuu.org.uk, peterz@infradead.org, ning.sun@intel.com, tboot-devel@lists.sourceforge.net, andi@firstfloor.org, luto@kernel.org, law@redhat.com, pbonzini@redhat.com, torvalds@linux-foundation.org, dwmw@amazon.co.uk, nickc@redhat.com, gregkh@linux-foundation.org Subject: [PATCH 4.14 101/118] x86/pti: Make unpoison of pgd for trusted boot work for real Date: Mon, 15 Jan 2018 13:35:28 +0100 Message-Id: <20180115123421.401337040@linuxfoundation.org> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20180115123415.325497625@linuxfoundation.org> References: <20180115123415.325497625@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dave Hansen commit 445b69e3b75e42362a5bdc13c8b8f61599e2228a upstream. The inital fix for trusted boot and PTI potentially misses the pgd clearing if pud_alloc() sets a PGD. It probably works in *practice* because for two adjacent calls to map_tboot_page() that share a PGD entry, the first will clear NX, *then* allocate and set the PGD (without NX clear). The second call will *not* allocate but will clear the NX bit. Defer the NX clearing to a point after it is known that all top-level allocations have occurred. Add a comment to clarify why. [ tglx: Massaged changelog ] Fixes: 262b6b30087 ("x86/tboot: Unbreak tboot with PTI enabled") Signed-off-by: Dave Hansen Signed-off-by: Thomas Gleixner Reviewed-by: Andrea Arcangeli Cc: Jon Masters Cc: "Tim Chen" Cc: gnomes@lxorguk.ukuu.org.uk Cc: peterz@infradead.org Cc: ning.sun@intel.com Cc: tboot-devel@lists.sourceforge.net Cc: andi@firstfloor.org Cc: luto@kernel.org Cc: law@redhat.com Cc: pbonzini@redhat.com Cc: torvalds@linux-foundation.org Cc: gregkh@linux-foundation.org Cc: dwmw@amazon.co.uk Cc: nickc@redhat.com Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20180110224939.2695CD47@viggo.jf.intel.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/tboot.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) --- a/arch/x86/kernel/tboot.c +++ b/arch/x86/kernel/tboot.c @@ -127,7 +127,6 @@ static int map_tboot_page(unsigned long p4d = p4d_alloc(&tboot_mm, pgd, vaddr); if (!p4d) return -1; - pgd->pgd &= ~_PAGE_NX; pud = pud_alloc(&tboot_mm, p4d, vaddr); if (!pud) return -1; @@ -139,6 +138,17 @@ static int map_tboot_page(unsigned long return -1; set_pte_at(&tboot_mm, vaddr, pte, pfn_pte(pfn, prot)); pte_unmap(pte); + + /* + * PTI poisons low addresses in the kernel page tables in the + * name of making them unusable for userspace. To execute + * code at such a low address, the poison must be cleared. + * + * Note: 'pgd' actually gets set in p4d_alloc() _or_ + * pud_alloc() depending on 4/5-level paging. + */ + pgd->pgd &= ~_PAGE_NX; + return 0; }