From: Andy Lutomirski <luto@kernel.org>
Date: Mon, 4 Dec 2017 15:07:45 +0100
Subject: x86/mm/pti: Share cpu_entry_area with user space page tables
Git-commit: f7cfbee91559ca7e3e961a00ffac921208a115ad
Patch-mainline: v4.15-rc6
References: bsc#1068032 CVE-2017-5754

Share the cpu entry area so the user space and kernel space page tables
have the same P4D page.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/mm/pti.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index d58bcee470fc..59290356f19f 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -265,6 +265,29 @@ pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)
 }
 
 /*
+ * Clone a single p4d (i.e. a top-level entry on 4-level systems and a
+ * next-level entry on 5-level systems.
+ */
+static void __init pti_clone_p4d(unsigned long addr)
+{
+	p4d_t *kernel_p4d, *user_p4d;
+	pgd_t *kernel_pgd;
+
+	user_p4d = pti_user_pagetable_walk_p4d(addr);
+	kernel_pgd = pgd_offset_k(addr);
+	kernel_p4d = p4d_offset(kernel_pgd, addr);
+	*user_p4d = *kernel_p4d;
+}
+
+/*
+ * Clone the CPU_ENTRY_AREA into the user space visible page table.
+ */
+static void __init pti_clone_user_shared(void)
+{
+	pti_clone_p4d(CPU_ENTRY_AREA_BASE);
+}
+
+/*
  * Initialize kernel page table isolation
  */
 void __init pti_init(void)
@@ -273,4 +296,6 @@ void __init pti_init(void)
 		return;
 
 	pr_info("enabled\n");
+
+	pti_clone_user_shared();
 }