From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f70.google.com (mail-pl0-f70.google.com [209.85.160.70]) by kanga.kvack.org (Postfix) with ESMTP id CE7F06B0009 for ; Tue, 3 Apr 2018 21:12:43 -0400 (EDT) Received: by mail-pl0-f70.google.com with SMTP id 91-v6so11992981pla.18 for ; Tue, 03 Apr 2018 18:12:43 -0700 (PDT) Received: from mga05.intel.com (mga05.intel.com. [192.55.52.43]) by mx.google.com with ESMTPS id u91-v6si1860593plb.698.2018.04.03.18.12.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 03 Apr 2018 18:12:42 -0700 (PDT) Subject: [PATCH 04/11] x86/espfix: document use of _PAGE_GLOBAL From: Dave Hansen Date: Tue, 03 Apr 2018 18:09:56 -0700 References: <20180404010946.6186729B@viggo.jf.intel.com> In-Reply-To: <20180404010946.6186729B@viggo.jf.intel.com> Message-Id: <20180404010956.32C1983F@viggo.jf.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Dave Hansen , aarcange@redhat.com, luto@kernel.org, torvalds@linux-foundation.org, keescook@google.com, hughd@google.com, jgross@suse.com, x86@kernel.org, namit@vmware.com From: Dave Hansen The "normal" kernel page table creation mechanisms using PAGE_KERNEL_* page protections will never set _PAGE_GLOBAL with PTI. The few places in the kernel that always want _PAGE_GLOBAL must avoid using PAGE_KERNEL_*. Document that we want it here and its use is not accidental. Signed-off-by: Dave Hansen Cc: Andrea Arcangeli Cc: Andy Lutomirski Cc: Linus Torvalds Cc: Kees Cook Cc: Hugh Dickins Cc: Juergen Gross Cc: x86@kernel.org Cc: Nadav Amit --- b/arch/x86/kernel/espfix_64.c | 4 ++++ 1 file changed, 4 insertions(+) diff -puN arch/x86/kernel/espfix_64.c~espfix-use-kern-defaults-not-supported arch/x86/kernel/espfix_64.c --- a/arch/x86/kernel/espfix_64.c~espfix-use-kern-defaults-not-supported 2018-04-02 16:41:14.274605175 -0700 +++ b/arch/x86/kernel/espfix_64.c 2018-04-02 16:41:14.278605175 -0700 @@ -195,6 +195,10 @@ void init_espfix_ap(int cpu) pte_p = pte_offset_kernel(&pmd, addr); stack_page = page_address(alloc_pages_node(node, GFP_KERNEL, 0)); + /* + * __PAGE_KERNEL_* includes _PAGE_GLOBAL, which we want since + * this is mapped to userspace. + */ pte = __pte(__pa(stack_page) | ((__PAGE_KERNEL_RO | _PAGE_ENC) & ptemask)); for (n = 0; n < ESPFIX_PTE_CLONES; n++) set_pte(&pte_p[n*PTE_STRIDE], pte); _