linux-kernel - [tip:x86/pti] x86/espfix: Document use of _PAGE

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Date:   Mon, 9 Apr 2018 10:13:17 -0700
From:   tip-bot for Dave Hansen <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     jpoimboe@...hat.com, torvalds@...ux-foundation.org,
        dave.hansen@...ux.intel.com, arjan@...ux.intel.com,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, namit@...are.com,
        bp@...en8.de, aarcange@...hat.com, luto@...nel.org,
        jgross@...e.com, keescook@...gle.com, gregkh@...uxfoundation.org,
        peterz@...radead.org, hpa@...or.com, dan.j.williams@...el.com,
        hughd@...gle.com, mingo@...nel.org, dwmw2@...radead.org
Subject: [tip:x86/pti] x86/espfix: Document use of _PAGE_GLOBAL

Commit-ID:  6baf4bec02dbc41645c3a5130ee15a8e1d62b80f
Gitweb:     https://git.kernel.org/tip/6baf4bec02dbc41645c3a5130ee15a8e1d62b80f
Author:     Dave Hansen <dave.hansen@...ux.intel.com>
AuthorDate: Fri, 6 Apr 2018 13:55:07 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 9 Apr 2018 18:27:33 +0200

x86/espfix: Document use of _PAGE_GLOBAL

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 <dave.hansen@...ux.intel.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Kees Cook <keescook@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Nadav Amit <namit@...are.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-mm@...ck.org
Link: http://lkml.kernel.org/r/20180406205507.BCF4D4F0@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/espfix_64.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
index e5ec3cafa72e..aebd0d5bc086 100644
--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -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);