powerpc/speculation: Support 'mitigations=' cmdline option

Configure powerpc CPU runtime speculation bug mitigations in accordance
with the 'mitigations=' cmdline option.  This affects Meltdown, Spectre
v1, Spectre v2, and Speculative Store Bypass.

The default behavior is unchanged.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jiri Kosina <jkosina@suse.cz> (on x86)
Reviewed-by: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Jon Masters <jcm@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: linux-s390@vger.kernel.org
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Phil Auld <pauld@redhat.com>
Link: https://lkml.kernel.org/r/245a606e1a42a558a310220312d9b6adb9159df6.1555085500.git.jpoimboe@redhat.com

CVE-2017-5715
CVE-2017-5753
CVE-2017-5754
CVE-2018-3639

(backported from commit 782e69ef https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git)
[juergh:
 - Dropped modifications of setup_barrier_nospec() and handle_nospectre_v2()
   (Xenial doesn't support nospectre_{v1,v2} kernel parameters for PPC).
 - Adjusted file path arch/powerpc/kernel/setup_64.c for modification of
   setup_stf_barrier().
 - Adjusted file path Documentation/kernel-parameters.txt.]
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

Documentation/kernel-parameters.txt

@@ -2258,7 +2258,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			http://repo.or.cz/w/linux-2.6/mini2440.git
 
 	mitigations=
-			[X86] Control optional mitigations for CPU
+			[X86,PPC] Control optional mitigations for CPU
 			vulnerabilities.  This is a set of curated,
 			arch-independent options, each of which is an
 			aggregation of existing arch-specific options.
@@ -2267,9 +2267,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 				Disable all optional CPU mitigations.  This
 				improves system performance, but it may also
 				expose users to several CPU vulnerabilities.
-				Equivalent to: nopti [X86]
+				Equivalent to: nopti [X86,PPC]
 					       nospectre_v2 [X86]
-					       spec_store_bypass_disable=off [X86]
+					       spec_store_bypass_disable=off [X86,PPC]
 					       l1tf=off [X86]
 
 			auto (default)

arch/powerpc/kernel/setup_64.c

@@ -39,6 +39,7 @@
 #include <linux/memory.h>
 #include <linux/nmi.h>
 #include <linux/debugfs.h>
+#include <linux/cpu.h>
 
 #include <asm/io.h>
 #include <asm/kdump.h>
@@ -957,7 +958,7 @@ void setup_stf_barrier(void)
 
 	stf_enabled_flush_types = type;
 
-	if (!no_stf_barrier)
+	if (!no_stf_barrier && !cpu_mitigations_off())
 		stf_barrier_enable(enable);
 }
 
@@ -1016,7 +1017,7 @@ void setup_rfi_flush(enum l1d_flush_type types, bool enable)
 
 	rfi_enabled_flush_types = types;
 
-	if (!no_rfi_flush)
+	if (!no_rfi_flush && !cpu_mitigations_off())
 		rfi_flush_enable(enable);
 }