Commit-ID:  6baf4bec02dbc41645c3a5130ee15a8e1d62b80f
Gitweb:     https://git.kernel.org/tip/6baf4bec02dbc41645c3a5130ee15a8e1d62b80f
Author:     Dave Hansen <dave.han...@linux.intel.com>
AuthorDate: Fri, 6 Apr 2018 13:55:07 -0700
Committer:  Ingo Molnar <mi...@kernel.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.han...@linux.intel.com>
Cc: Andrea Arcangeli <aarca...@redhat.com>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Arjan van de Ven <ar...@linux.intel.com>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Dan Williams <dan.j.willi...@intel.com>
Cc: David Woodhouse <dw...@infradead.org>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Hugh Dickins <hu...@google.com>
Cc: Josh Poimboeuf <jpoim...@redhat.com>
Cc: Juergen Gross <jgr...@suse.com>
Cc: Kees Cook <keesc...@google.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Nadav Amit <na...@vmware.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: linux...@kvack.org
Link: http://lkml.kernel.org/r/20180406205507.bcf4d...@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mi...@kernel.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);

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