x86/bugs: Provide boot parameters for the spec_store_bypass_disable mitigation

[mirror_ubuntu-artful-kernel.git] / arch / x86 / kernel / cpu / bugs.c

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 51afebd7c3b1dad1cc44d13c13db7adffe32e356..2e99df202a96912c4ac2049b97c775feee5cae19 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -26,6 +26,7 @@
 #include <asm/intel-family.h>
 
 static void __init spectre_v2_select_mitigation(void);
+static void __init ssb_select_mitigation(void);
 
 /*
  * Our boot-time value of the SPEC_CTRL MSR. We read it once so that any
@@ -52,6 +53,12 @@ void __init check_bugs(void)
        /* Select the proper spectre mitigation before patching alternatives */
        spectre_v2_select_mitigation();
 
+       /*
+        * Select proper mitigation for any exposure to the Speculative Store
+        * Bypass vulnerability.
+        */
+       ssb_select_mitigation();
+
 #ifdef CONFIG_X86_32
        /*
         * Check whether we are able to run this kernel safely on SMP.
@@ -316,6 +323,99 @@ retpoline_auto:
        }
 }
 
+#undef pr_fmt
+#define pr_fmt(fmt)    "Speculative Store Bypass: " fmt
+
+static enum ssb_mitigation ssb_mode = SPEC_STORE_BYPASS_NONE;
+
+/* The kernel command line selection */
+enum ssb_mitigation_cmd {
+       SPEC_STORE_BYPASS_CMD_NONE,
+       SPEC_STORE_BYPASS_CMD_AUTO,
+       SPEC_STORE_BYPASS_CMD_ON,
+};
+
+static const char *ssb_strings[] = {
+       [SPEC_STORE_BYPASS_NONE]        = "Vulnerable",
+       [SPEC_STORE_BYPASS_DISABLE]     = "Mitigation: Speculative Store Bypass disabled"
+};
+
+static const struct {
+       const char *option;
+       enum ssb_mitigation_cmd cmd;
+} ssb_mitigation_options[] = {
+       { "auto",       SPEC_STORE_BYPASS_CMD_AUTO }, /* Platform decides */
+       { "on",         SPEC_STORE_BYPASS_CMD_ON },   /* Disable Speculative Store Bypass */
+       { "off",        SPEC_STORE_BYPASS_CMD_NONE }, /* Don't touch Speculative Store Bypass */
+};
+
+static enum ssb_mitigation_cmd __init ssb_parse_cmdline(void)
+{
+       enum ssb_mitigation_cmd cmd = SPEC_STORE_BYPASS_CMD_AUTO;
+       char arg[20];
+       int ret, i;
+
+       if (cmdline_find_option_bool(boot_command_line, "nospec_store_bypass_disable")) {
+               return SPEC_STORE_BYPASS_CMD_NONE;
+       } else {
+               ret = cmdline_find_option(boot_command_line, "spec_store_bypass_disable",
+                                         arg, sizeof(arg));
+               if (ret < 0)
+                       return SPEC_STORE_BYPASS_CMD_AUTO;
+
+               for (i = 0; i < ARRAY_SIZE(ssb_mitigation_options); i++) {
+                       if (!match_option(arg, ret, ssb_mitigation_options[i].option))
+                               continue;
+
+                       cmd = ssb_mitigation_options[i].cmd;
+                       break;
+               }
+
+               if (i >= ARRAY_SIZE(ssb_mitigation_options)) {
+                       pr_err("unknown option (%s). Switching to AUTO select\n", arg);
+                       return SPEC_STORE_BYPASS_CMD_AUTO;
+               }
+       }
+
+       return cmd;
+}
+
+static enum ssb_mitigation_cmd __init __ssb_select_mitigation(void)
+{
+       enum ssb_mitigation mode = SPEC_STORE_BYPASS_NONE;
+       enum ssb_mitigation_cmd cmd;
+
+       if (!boot_cpu_has(X86_FEATURE_RDS))
+               return mode;
+
+       cmd = ssb_parse_cmdline();
+       if (!boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS) &&
+           (cmd == SPEC_STORE_BYPASS_CMD_NONE ||
+            cmd == SPEC_STORE_BYPASS_CMD_AUTO))
+               return mode;
+
+       switch (cmd) {
+       case SPEC_STORE_BYPASS_CMD_AUTO:
+       case SPEC_STORE_BYPASS_CMD_ON:
+               mode = SPEC_STORE_BYPASS_DISABLE;
+               break;
+       case SPEC_STORE_BYPASS_CMD_NONE:
+               break;
+       }
+
+       if (mode != SPEC_STORE_BYPASS_NONE)
+               setup_force_cpu_cap(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE);
+       return mode;
+}
+
+static void ssb_select_mitigation()
+{
+       ssb_mode = __ssb_select_mitigation();
+
+       if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS))
+               pr_info("%s\n", ssb_strings[ssb_mode]);
+}
+
 #undef pr_fmt
 
 #ifdef CONFIG_SYSFS
@@ -338,6 +438,9 @@ ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
        case X86_BUG_SPECTRE_V2:
                return sprintf(buf, "%s%s\n", spectre_v2_strings[spectre_v2_enabled], ibpb_inuse ? ", IBPB (Intel v4)" : "");
 
+       case X86_BUG_SPEC_STORE_BYPASS:
+               return sprintf(buf, "%s\n", ssb_strings[ssb_mode]);
+
        default:
                break;
        }