x86/pti: Add the pti= cmdline option and documentation

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>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5dfd262..520fdec 100644 (file)
--- 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 375f23a..a13f6b1 100644 (file)
--- 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);
 }