x86/speculation: Support 'mitigations=' cmdline option

commit d68be4c4d31295ff6ae34a8ddfaa4c1a8ff42812 upstream.

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
[bwh: Backported to 4.9: adjust filenames, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 23af0af..5f81df1 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2474,15 +2474,20 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                        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
@@ -2490,12 +2495,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                                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

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index d81f55e..c2e07be 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -500,7 +500,8 @@ 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));
@@ -764,7 +765,8 @@ 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",
@@ -1085,6 +1087,11 @@ 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) {

diff --git a/arch/x86/mm/kaiser.c b/arch/x86/mm/kaiser.c
index 3f729e2..12522db 100644 (file)
--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -9,6 +9,7 @@
 #include <linux/spinlock.h>
 #include <linux/mm.h>
 #include <linux/uaccess.h>
+#include <linux/cpu.h>
 
 #undef pr_fmt
 #define pr_fmt(fmt)     "Kernel/User page tables isolation: " fmt
@@ -297,7 +298,8 @@ void __init kaiser_check_boottime_disable(void)
                        goto skip;
        }
 
-       if (cmdline_find_option_bool(boot_command_line, "nopti"))
+       if (cmdline_find_option_bool(boot_command_line, "nopti") ||
+           cpu_mitigations_off())
                goto disable;
 
 skip: