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

* [PATCH] x86/pti: Add pti= cmdline option and documentation
@ 2017-12-12 13:39 Borislav Petkov
  2017-12-12 13:46 ` Juergen Gross
  2017-12-12 14:28 ` Will Deacon
  0 siblings, 2 replies; 5+ messages in thread
From: Borislav Petkov @ 2017-12-12 13:39 UTC (permalink / raw)
  To: X86 ML
  Cc: LKML, Linus Torvalds, Andy Lutomirsky, Peter Zijlstra,
	Dave Hansen, Greg KH, keescook, hughd, Brian Gerst,
	Josh Poimboeuf, Denys Vlasenko, Boris Ostrovsky, Juergen Gross,
	David Laight, Eduardo Valentin, aliguori, Will Deacon,
	daniel.gruss

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

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