From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752799AbeAJWvp (ORCPT + 1 other); Wed, 10 Jan 2018 17:51:45 -0500 Received: from mga14.intel.com ([192.55.52.115]:54581 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752096AbeAJWvo (ORCPT ); Wed, 10 Jan 2018 17:51:44 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,342,1511856000"; d="scan'208";a="23036976" Subject: [PATCH] x86/pti: unpoison pgd for trusted boot To: linux-kernel@vger.kernel.org Cc: x86@kernel.org, Dave Hansen , ning.sun@intel.com, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, tboot-devel@lists.sourceforge.net, aarcange@redhat.com, jcm@redhat.com, dwmw@amazon.co.uk, pbonzini@redhat.com, gnomes@lxorguk.ukuu.org.uk, torvalds@linux-foundation.org, andi@firstfloor.org, gregkh@linux-foundation.org, tim.c.chen@linux.intel.com, law@redhat.com, nickc@redhat.com, luto@kernel.org, peterz@infradead.org From: Dave Hansen Date: Wed, 10 Jan 2018 14:49:39 -0800 Message-Id: <20180110224939.2695CD47@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: Updated to make this on top of x86/pti. -- From: Dave Hansen The code in -tip potentially misses the pgd clearing if pud_alloc() sets a PGD. It would also be nice to have that comment back. Note that the -tip commit 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. This just defers the NX clearing to a point after it is known that all top-level allocations have occurred. Add a comment to clarify why. Fixes: 262b6b30087 ("x86/tboot: Unbreak tboot with PTI enabled") Signed-off-by: Dave Hansen Cc: Ning Sun Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Cc: tboot-devel@lists.sourceforge.net Cc: linux-kernel@vger.kernel.org Cc: Andrea Arcangeli CC: Jon Masters Cc: "Woodhouse, David" Cc: Paolo Bonzini Cc: Alan Cox Cc: Linus Torvalds Cc: Andi Kleen Cc: Greg Kroah-Hartman CC: "Tim Chen" Cc: Jeff Law Cc: Nick Clifton Cc: Andy Lutomirski Cc: Peter Zijlstra --- b/arch/x86/kernel/tboot.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff -puN arch/x86/kernel/tboot.c~pti-tboot-fix arch/x86/kernel/tboot.c --- a/arch/x86/kernel/tboot.c~pti-tboot-fix 2018-01-10 14:24:46.454544324 -0800 +++ b/arch/x86/kernel/tboot.c 2018-01-10 14:25:53.354544157 -0800 @@ -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; } _