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 <jpoim...@redhat.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 16 +++++++++++-----
 arch/x86/kernel/cpu/bugs.c                      | 11 +++++++++--
 arch/x86/mm/pti.c                               |  4 +++-
 3 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt 
b/Documentation/admin-guide/kernel-parameters.txt
index 3ea92e075c64..3e33bd03441a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2545,15 +2545,20 @@
                        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
@@ -2561,12 +2566,13 @@
                                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
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 2da82eff0eb4..8043a21f36be 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -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",
@@ -1008,6 +1010,11 @@ 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/pti.c b/arch/x86/mm/pti.c
index 5d27172c683f..9c2463bc158f 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -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;
-- 
2.17.2

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