Commit d68be4c4 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Thomas Gleixner
Browse files

x86/speculation: Support 'mitigations=' cmdline option 



Configure x86 runtime CPU speculation bug mitigations in accordance with
the 'mitigations=' cmdline option.  This affects Meltdown, Spectre v2,
Speculative Store Bypass, and L1TF.

The default behavior is unchanged.

Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: Jiri Kosina <jkosina@suse.cz> (on x86)
Reviewed-by: default avatarJiri 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/6616d0ae169308516cfdf5216bedd169f8a8291b.1555085500.git.jpoimboe@redhat.com
parent 98af8452

Documentation/admin-guide/kernel-parameters.txt

+11 −5
Original line number Diff line number Diff line
@@ -2514,15 +2514,20 @@ 
			http://repo.or.cz/w/linux-2.6/mini2440.git



	mitigations=

			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.

			[X86] 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.



			off

				Disable all optional CPU mitigations.  This

				improves system performance, but it may also

				expose users to several CPU vulnerabilities.

				Equivalent to: nopti [X86]

					       nospectre_v2 [X86]

					       spectre_v2_user=off [X86]

					       spec_store_bypass_disable=off [X86]

					       l1tf=off [X86]



			auto (default)

				Mitigate all CPU vulnerabilities, but leave SMT
@@ -2530,12 +2535,13 @@ 
				users who don't want to be surprised by SMT

				getting disabled across kernel upgrades, or who

				have other ways of avoiding SMT-based attacks.

				This is the default behavior.

				Equivalent to: (default behavior)



			auto,nosmt

				Mitigate all CPU vulnerabilities, disabling SMT

				if needed.  This is for users who always want to

				be fully mitigated, even if it means losing SMT.

				Equivalent to: l1tf=flush,nosmt [X86]



	mminit_loglevel=

			[KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this

arch/x86/kernel/cpu/bugs.c

+9 −2
Original line number Diff line number Diff line
@@ -440,7 +440,8 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) 
	char arg[20];

	int ret, i;



	if (cmdline_find_option_bool(boot_command_line, "nospectre_v2"))

	if (cmdline_find_option_bool(boot_command_line, "nospectre_v2") ||

	    cpu_mitigations_off())

		return SPECTRE_V2_CMD_NONE;



	ret = cmdline_find_option(boot_command_line, "spectre_v2", arg, sizeof(arg));
@@ -672,7 +673,8 @@ static enum ssb_mitigation_cmd __init ssb_parse_cmdline(void) 
	char arg[20];

	int ret, i;



	if (cmdline_find_option_bool(boot_command_line, "nospec_store_bypass_disable")) {

	if (cmdline_find_option_bool(boot_command_line, "nospec_store_bypass_disable") ||

	    cpu_mitigations_off()) {

		return SPEC_STORE_BYPASS_CMD_NONE;

	} else {

		ret = cmdline_find_option(boot_command_line, "spec_store_bypass_disable",
@@ -996,6 +998,11 @@ static void __init l1tf_select_mitigation(void) 
	if (!boot_cpu_has_bug(X86_BUG_L1TF))

		return;



	if (cpu_mitigations_off())

		l1tf_mitigation = L1TF_MITIGATION_OFF;

	else if (cpu_mitigations_auto_nosmt())

		l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;



	override_cache_bits(&boot_cpu_data);



	switch (l1tf_mitigation) {

arch/x86/mm/pti.c

+3 −1
Original line number Diff line number Diff line
@@ -35,6 +35,7 @@ 
#include <linux/spinlock.h>

#include <linux/mm.h>

#include <linux/uaccess.h>

#include <linux/cpu.h>



#include <asm/cpufeature.h>

#include <asm/hypervisor.h>
@@ -115,7 +116,8 @@ void __init pti_check_boottime_disable(void) 
		}

	}



	if (cmdline_find_option_bool(boot_command_line, "nopti")) {

	if (cmdline_find_option_bool(boot_command_line, "nopti") ||

	    cpu_mitigations_off()) {

		pti_mode = PTI_FORCE_OFF;

		pti_print_if_insecure("disabled on command line.");

		return;

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