[PATCH] x86/pti: Add pti= cmdline option and documentation

[Borislav Petkov <bp@alien8.de>]

From: Borislav Petkov <bp@suse.de>

Keep the "nopti" for traditional reasons.

Requested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: keescook@google.com
Cc: hughd@google.com
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: aliguori@amazon.com
Cc: Will Deacon <will.deacon@arm.com>
Cc: daniel.gruss@iaik.tugraz.at
---
 Documentation/admin-guide/kernel-parameters.txt |  6 ++++++
 arch/x86/mm/pti.c                               | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5dfd26265484..520fdec15bbb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3255,6 +3255,12 @@
 	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 f48645d2f3fd..4afa16b444b2 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -51,15 +51,33 @@
 void __init pti_check_boottime_disable(void)
 {
 	bool enable = true;
+	char arg[5];
+
+	if (cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg))) {
+		if (!strncmp(arg, "on", 2))
+			goto enable;
+
+		if (!strncmp(arg, "off", 3)) {
+			pr_info("disabled on command line.\n");
+			return;
+		}
+
+		if (!strncmp(arg, "auto", 4))
+			goto skip;
+	}
 
 	if (cmdline_find_option_bool(boot_command_line, "nopti")) {
 		pr_info("disabled on command line.\n");
 		enable = false;
 	}
+
+skip:
 	if (hypervisor_is_type(X86_HYPER_XEN_PV)) {
 		pr_info("disabled on XEN_PV.\n");
 		enable = false;
 	}
+
+enable:
 	if (enable)
 		setup_force_cpu_bug(X86_BUG_CPU_SECURE_MODE_PTI);
 }
-- 
2.13.0