[patch 30/60] x86/mm/kpti: Add infrastructure for page table isolation

[Thomas Gleixner]

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

Add the initial files for kernel page table isolation, with a minimal init
function and the boot time detection for this misfeature.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt |    2 
 arch/x86/boot/compressed/pagetable.c            |    3 
 arch/x86/entry/calling.h                        |    7 ++
 arch/x86/include/asm/kpti.h                     |   14 ++++
 arch/x86/mm/Makefile                            |    7 +-
 arch/x86/mm/init.c                              |    2 
 arch/x86/mm/kpti.c                              |   76 ++++++++++++++++++++++++
 include/linux/kpti.h                            |   11 +++
 init/main.c                                     |    2 
 9 files changed, 121 insertions(+), 3 deletions(-)

--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2711,6 +2711,8 @@
 			steal time is computed, but won't influence scheduler
 			behaviour
 
+	nokpti		[X86-64] Disable kernel page table isolation
+
 	nolapic		[X86-32,APIC] Do not enable or use the local APIC.
 
 	nolapic_timer	[X86-32,APIC] Do not use the local APIC timer.
--- a/arch/x86/boot/compressed/pagetable.c
+++ b/arch/x86/boot/compressed/pagetable.c
@@ -23,6 +23,9 @@
  */
 #undef CONFIG_AMD_MEM_ENCRYPT
 
+/* No KERNEL_PAGE_TABLE_ISOLATION support needed either: */
+#undef CONFIG_KERNEL_PAGE_TABLE_ISOLATION
+
 #include "misc.h"
 
 /* These actually do the work of building the kernel identity maps. */
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -205,18 +205,23 @@ For 32-bit we have the following convent
 .endm
 
 .macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
+	ALTERNATIVE "jmp .Lend_\@", "", X86_BUG_CPU_SECURE_MODE_KPTI
 	mov	%cr3, \scratch_reg
 	ADJUST_KERNEL_CR3 \scratch_reg
 	mov	\scratch_reg, %cr3
+.Lend_\@:
 .endm
 
 .macro SWITCH_TO_USER_CR3 scratch_reg:req
+	ALTERNATIVE "jmp .Lend_\@", "", X86_BUG_CPU_SECURE_MODE_KPTI
 	mov	%cr3, \scratch_reg
 	ADJUST_USER_CR3 \scratch_reg
 	mov	\scratch_reg, %cr3
+.Lend_\@:
 .endm
 
 .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
+	ALTERNATIVE "jmp .Ldone_\@", "", X86_BUG_CPU_SECURE_MODE_KPTI
 	movq	%cr3, \scratch_reg
 	movq	\scratch_reg, \save_reg
 	/*
@@ -233,11 +238,13 @@ For 32-bit we have the following convent
 .endm
 
 .macro RESTORE_CR3 save_reg:req
+	ALTERNATIVE "jmp .Lend_\@", "", X86_BUG_CPU_SECURE_MODE_KPTI
 	/*
 	 * The CR3 write could be avoided when not changing its value,
 	 * but would require a CR3 read *and* a scratch register.
 	 */
 	movq	\save_reg, %cr3
+.Lend_\@:
 .endm
 
 #else /* CONFIG_KERNEL_PAGE_TABLE_ISOLATION=n: */
--- /dev/null
+++ b/arch/x86/include/asm/kpti.h
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef _ASM_X86_KPTI_H
+#define _ASM_X86_KPTI_H
+#ifndef __ASSEMBLY__
+
+#ifdef CONFIG_KERNEL_PAGE_TABLE_ISOLATION
+extern void kpti_init(void);
+extern void kpti_check_boottime_disable(void);
+#else
+static inline void kpti_check_boottime_disable(void) { }
+#endif
+
+#endif /* __ASSEMBLY__ */
+#endif /* _ASM_X86_KPTI_H */
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -43,9 +43,10 @@ obj-$(CONFIG_AMD_NUMA)		+= amdtopology.o
 obj-$(CONFIG_ACPI_NUMA)		+= srat.o
 obj-$(CONFIG_NUMA_EMU)		+= numa_emulation.o
 
-obj-$(CONFIG_X86_INTEL_MPX)	+= mpx.o
-obj-$(CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) += pkeys.o
-obj-$(CONFIG_RANDOMIZE_MEMORY) += kaslr.o
+obj-$(CONFIG_X86_INTEL_MPX)			+= mpx.o
+obj-$(CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) 	+= pkeys.o
+obj-$(CONFIG_RANDOMIZE_MEMORY) 			+= kaslr.o
+obj-$(CONFIG_KERNEL_PAGE_TABLE_ISOLATION)	+= kpti.o
 
 obj-$(CONFIG_AMD_MEM_ENCRYPT)	+= mem_encrypt.o
 obj-$(CONFIG_AMD_MEM_ENCRYPT)	+= mem_encrypt_boot.o
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -20,6 +20,7 @@
 #include <asm/kaslr.h>
 #include <asm/hypervisor.h>
 #include <asm/cpufeature.h>
+#include <asm/kpti.h>
 
 /*
  * We need to define the tracepoints somewhere, and tlb.c
@@ -630,6 +631,7 @@ void __init init_mem_mapping(void)
 {
 	unsigned long end;
 
+	kpti_check_boottime_disable();
 	probe_page_size_mask();
 	setup_pcid();
 
--- /dev/null
+++ b/arch/x86/mm/kpti.c
@@ -0,0 +1,76 @@
+/*
+ * Copyright(c) 2017 Intel Corporation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * This code is based in part on work published here:
+ *
+ *	https://github.com/IAIK/KAISER
+ *
+ * The original work was written by and and signed off by for the Linux
+ * kernel by:
+ *
+ *   Signed-off-by: Richard Fellner <richard.fellner@xxxxxxxxxxxxxxxxx>
+ *   Signed-off-by: Moritz Lipp <moritz.lipp@xxxxxxxxxxxxxx>
+ *   Signed-off-by: Daniel Gruss <daniel.gruss@xxxxxxxxxxxxxx>
+ *   Signed-off-by: Michael Schwarz <michael.schwarz@xxxxxxxxxxxxxx>
+ *
+ * Major changes to the original code by: Dave Hansen <dave.hansen@xxxxxxxxx>
+ * Mostly rewritten by Thomas Gleixner <tglx@xxxxxxxxxxxxx> and
+ *		       Andy Lutomirsky <luto@xxxxxxxxxxxxxx>
+ */
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/bug.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/mm.h>
+#include <linux/uaccess.h>
+
+#include <asm/cpufeature.h>
+#include <asm/hypervisor.h>
+#include <asm/cmdline.h>
+#include <asm/kpti.h>
+#include <asm/pgtable.h>
+#include <asm/pgalloc.h>
+#include <asm/tlbflush.h>
+#include <asm/desc.h>
+
+#undef pr_fmt
+#define pr_fmt(fmt)     "Kernel/User page tables isolation: " fmt
+
+void __init kpti_check_boottime_disable(void)
+{
+	bool enable = true;
+
+	if (cmdline_find_option_bool(boot_command_line, "nokpti")) {
+		pr_info("disabled on command line.\n");
+		enable = false;
+	}
+	if (hypervisor_is_type(X86_HYPER_XEN_PV)) {
+		pr_info("disabled on XEN_PV.\n");
+		enable = false;
+	}
+	if (enable)
+		setup_force_cpu_bug(X86_BUG_CPU_SECURE_MODE_KPTI);
+}
+
+/*
+ * Initialize kernel page table isolation
+ */
+void __init kpti_init(void)
+{
+	if (!static_cpu_has_bug(X86_BUG_CPU_SECURE_MODE_KPTI))
+		return;
+
+	pr_info("enabled\n");
+}
--- /dev/null
+++ b/include/linux/kpti.h
@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef _INCLUDE_KPTI_H
+#define _INCLUDE_KPTI_H
+
+#ifdef CONFIG_KERNEL_PAGE_TABLE_ISOLATION
+#include <asm/kpti.h>
+#else
+static inline void kpti_init(void) { }
+#endif
+
+#endif
--- a/init/main.c
+++ b/init/main.c
@@ -76,6 +76,7 @@
 #include <linux/slab.h>
 #include <linux/perf_event.h>
 #include <linux/ptrace.h>
+#include <linux/kpti.h>
 #include <linux/blkdev.h>
 #include <linux/elevator.h>
 #include <linux/sched_clock.h>
@@ -505,6 +506,7 @@ static void __init mm_init(void)
 	pgtable_init();
 	vmalloc_init();
 	ioremap_huge_init();
+	kpti_init();
 }
 
 asmlinkage __visible void __init start_kernel(void)