From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Borislav Petkov <bp@suse.de>
Date: Tue, 12 Dec 2017 14:39:52 +0100
Subject: [PATCH] x86/pti: Add the pti= cmdline option and documentation
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CVE-2017-5754

Keep the "nopti" optional for traditional reasons.

[ tglx: Don't allow force on when running on XEN PV and made 'on'
	printout conditional ]

Requested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.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
Link: https://lkml.kernel.org/r/20171212133952.10177-1-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 41f4c20b57a4890ea7f56ff8717cc83fefb8d537)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
(cherry picked from commit 96d3670fa8f88989fb7c0be5172a1378143f3296)
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  6 ++++++
 arch/x86/mm/pti.c                               | 26 ++++++++++++++++++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index e2a4608da5d2..b4d2edf316db 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3247,6 +3247,12 @@
 	pt.		[PARIDE]
 			See Documentation/blockdev/paride.txt.
 
+	pti=		[X86_64]
+			Control user/kernel address space isolation:
+			on - enable
+			off - disable
+			auto - default setting
+
 	pty.legacy_count=
 			[KNL] Number of legacy pty's. Overwrites compiled-in
 			default number.
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 375f23a758bc..a13f6b109865 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -54,21 +54,45 @@ static void __init pti_print_if_insecure(const char *reason)
 		pr_info("%s\n", reason);
 }
 
+static void __init pti_print_if_secure(const char *reason)
+{
+	if (!boot_cpu_has_bug(X86_BUG_CPU_INSECURE))
+		pr_info("%s\n", reason);
+}
+
 void __init pti_check_boottime_disable(void)
 {
+	char arg[5];
+	int ret;
+
 	if (hypervisor_is_type(X86_HYPER_XEN_PV)) {
 		pti_print_if_insecure("disabled on XEN PV.");
 		return;
 	}
 
+	ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg));
+	if (ret > 0)  {
+		if (ret == 3 && !strncmp(arg, "off", 3)) {
+			pti_print_if_insecure("disabled on command line.");
+			return;
+		}
+		if (ret == 2 && !strncmp(arg, "on", 2)) {
+			pti_print_if_secure("force enabled on command line.");
+			goto enable;
+		}
+		if (ret == 4 && !strncmp(arg, "auto", 4))
+			goto autosel;
+	}
+
 	if (cmdline_find_option_bool(boot_command_line, "nopti")) {
 		pti_print_if_insecure("disabled on command line.");
 		return;
 	}
 
+autosel:
 	if (!boot_cpu_has_bug(X86_BUG_CPU_INSECURE))
 		return;
-
+enable:
 	setup_force_cpu_cap(X86_FEATURE_PTI);
 }
 
-- 
2.14.2

