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x86/speculation: Support 'mitigations=' cmdline option
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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: 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/6616d0ae169308516cfdf5216bedd169f8a8291b.1555085500.git.jpoimboe@redhat.com
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Josh Poimboeuf authored and Thomas Gleixner committed Apr 17, 2019
1 parent 98af845 commit d68be4c
Showing 3 changed files with 23 additions and 8 deletions.
16 changes: 11 additions & 5 deletions Documentation/admin-guide/kernel-parameters.txt
Original file line number Diff line number Diff line change
@@ -2514,28 +2514,34 @@
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
enabled, even if it's vulnerable. This is for
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
11 changes: 9 additions & 2 deletions arch/x86/kernel/cpu/bugs.c
Original file line number Diff line number Diff line change
@@ -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) {
4 changes: 3 additions & 1 deletion arch/x86/mm/pti.c
Original file line number Diff line number Diff line change
@@ -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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