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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham 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 79519C64EAD for ; Sat, 29 Sep 2018 21:55:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 495082087A for ; Sat, 29 Sep 2018 21:55:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 495082087A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=decadent.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728558AbeI3ES2 (ORCPT ); Sun, 30 Sep 2018 00:18:28 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:51648 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726630AbeI3ESY (ORCPT ); Sun, 30 Sep 2018 00:18:24 -0400 Received: from [2a02:8011:400e:2:cbab:f00:c93f:614] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.84_2) (envelope-from ) id 1g6N63-0000HA-D0; Sat, 29 Sep 2018 22:48:19 +0100 Received: from ben by deadeye with local (Exim 4.91) (envelope-from ) id 1g6N5z-0006yH-EJ; Sat, 29 Sep 2018 22:48:15 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Sean Christopherson" , "Andi Kleen" , "Michal Hocko" , "Dave Hansen" , "Vlastimil Babka" , "Linus Torvalds" , "Thomas Gleixner" , "Josh Poimboeuf" , "Greg Kroah-Hartman" Date: Sat, 29 Sep 2018 22:43:07 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 117/131] x86/speculation/l1tf: Exempt zeroed PTEs from inversion In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:cbab:f00:c93f:614 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.59-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Sean Christopherson commit f19f5c49bbc3ffcc9126cc245fc1b24cc29f4a37 upstream. It turns out that we should *not* invert all not-present mappings, because the all zeroes case is obviously special. clear_page() does not undergo the XOR logic to invert the address bits, i.e. PTE, PMD and PUD entries that have not been individually written will have val=0 and so will trigger __pte_needs_invert(). As a result, {pte,pmd,pud}_pfn() will return the wrong PFN value, i.e. all ones (adjusted by the max PFN mask) instead of zero. A zeroed entry is ok because the page at physical address 0 is reserved early in boot specifically to mitigate L1TF, so explicitly exempt them from the inversion when reading the PFN. Manifested as an unexpected mprotect(..., PROT_NONE) failure when called on a VMA that has VM_PFNMAP and was mmap'd to as something other than PROT_NONE but never used. mprotect() sends the PROT_NONE request down prot_none_walk(), which walks the PTEs to check the PFNs. prot_none_pte_entry() gets the bogus PFN from pte_pfn() and returns -EACCES because it thinks mprotect() is trying to adjust a high MMIO address. [ This is a very modified version of Sean's original patch, but all credit goes to Sean for doing this and also pointing out that sometimes the __pte_needs_invert() function only gets the protection bits, not the full eventual pte. But zero remains special even in just protection bits, so that's ok. - Linus ] Fixes: f22cc87f6c1f ("x86/speculation/l1tf: Invert all not present mappings") Signed-off-by: Sean Christopherson Acked-by: Andi Kleen Cc: Thomas Gleixner Cc: Josh Poimboeuf Cc: Michal Hocko Cc: Vlastimil Babka Cc: Dave Hansen Cc: Greg Kroah-Hartman Signed-off-by: Linus Torvalds Signed-off-by: Ben Hutchings --- arch/x86/include/asm/pgtable-invert.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) --- a/arch/x86/include/asm/pgtable-invert.h +++ b/arch/x86/include/asm/pgtable-invert.h @@ -4,9 +4,18 @@ #ifndef __ASSEMBLY__ +/* + * A clear pte value is special, and doesn't get inverted. + * + * Note that even users that only pass a pgprot_t (rather + * than a full pte) won't trigger the special zero case, + * because even PAGE_NONE has _PAGE_PROTNONE | _PAGE_ACCESSED + * set. So the all zero case really is limited to just the + * cleared page table entry case. + */ static inline bool __pte_needs_invert(u64 val) { - return !(val & _PAGE_PRESENT); + return val && !(val & _PAGE_PRESENT); } /* Get a mask to xor with the page table entry to get the correct pfn. */