1 files changed, 221 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index ba0b2424c9b0..390b3dc3d438 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -10,6 +10,10 @@
  */
 #include <linux/init.h>
 #include <linux/utsname.h>
+#include <linux/cpu.h>
+
+#include <asm/nospec-branch.h>
+#include <asm/cmdline.h>
 #include <asm/bugs.h>
 #include <asm/processor.h>
 #include <asm/processor-flags.h>
@@ -19,6 +23,9 @@
 #include <asm/alternative.h>
 #include <asm/pgtable.h>
 #include <asm/set_memory.h>
+#include <asm/intel-family.h>
+
+static void __init spectre_v2_select_mitigation(void);
 
 void __init check_bugs(void)
 {
@@ -29,6 +36,9 @@ void __init check_bugs(void)
                 print_cpu_info(&boot_cpu_data);
         }
 
+        /* Select the proper spectre mitigation before patching alternatives */
+        spectre_v2_select_mitigation();
+
 #ifdef CONFIG_X86_32
         /*
          * Check whether we are able to run this kernel safely on SMP.
@@ -60,3 +70,214 @@ void __init check_bugs(void)
                 set_memory_4k((unsigned long)__va(0), 1);
 #endif
 }
+
+/* The kernel command line selection */
+enum spectre_v2_mitigation_cmd {
+        SPECTRE_V2_CMD_NONE,
+        SPECTRE_V2_CMD_AUTO,
+        SPECTRE_V2_CMD_FORCE,
+        SPECTRE_V2_CMD_RETPOLINE,
+        SPECTRE_V2_CMD_RETPOLINE_GENERIC,
+        SPECTRE_V2_CMD_RETPOLINE_AMD,
+};
+
+static const char *spectre_v2_strings[] = {
+        [SPECTRE_V2_NONE]                       = "Vulnerable",
+        [SPECTRE_V2_RETPOLINE_MINIMAL]          = "Vulnerable: Minimal generic ASM retpoline",
+        [SPECTRE_V2_RETPOLINE_MINIMAL_AMD]      = "Vulnerable: Minimal AMD ASM retpoline",
+        [SPECTRE_V2_RETPOLINE_GENERIC]          = "Mitigation: Full generic retpoline",
+        [SPECTRE_V2_RETPOLINE_AMD]              = "Mitigation: Full AMD retpoline",
+};
+
+#undef pr_fmt
+#define pr_fmt(fmt)     "Spectre V2 mitigation: " fmt
+
+static enum spectre_v2_mitigation spectre_v2_enabled = SPECTRE_V2_NONE;
+
+static void __init spec2_print_if_insecure(const char *reason)
+{
+        if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
+                pr_info("%s\n", reason);
+}
+
+static void __init spec2_print_if_secure(const char *reason)
+{
+        if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
+                pr_info("%s\n", reason);
+}
+
+static inline bool retp_compiler(void)
+{
+        return __is_defined(RETPOLINE);
+}
+
+static inline bool match_option(const char *arg, int arglen, const char *opt)
+{
+        int len = strlen(opt);
+
+        return len == arglen && !strncmp(arg, opt, len);
+}
+
+static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
+{
+        char arg[20];
+        int ret;
+
+        ret = cmdline_find_option(boot_command_line, "spectre_v2", arg,
+                                  sizeof(arg));
+        if (ret > 0)  {
+                if (match_option(arg, ret, "off")) {
+                        goto disable;
+                } else if (match_option(arg, ret, "on")) {
+                        spec2_print_if_secure("force enabled on command line.");
+                        return SPECTRE_V2_CMD_FORCE;
+                } else if (match_option(arg, ret, "retpoline")) {
+                        spec2_print_if_insecure("retpoline selected on command line.");
+                        return SPECTRE_V2_CMD_RETPOLINE;
+                } else if (match_option(arg, ret, "retpoline,amd")) {
+                        if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
+                                pr_err("retpoline,amd selected but CPU is not AMD. Switching to AUTO select\n");
+                                return SPECTRE_V2_CMD_AUTO;
+                        }
+                        spec2_print_if_insecure("AMD retpoline selected on command line.");
+                        return SPECTRE_V2_CMD_RETPOLINE_AMD;
+                } else if (match_option(arg, ret, "retpoline,generic")) {
+                        spec2_print_if_insecure("generic retpoline selected on command line.");
+                        return SPECTRE_V2_CMD_RETPOLINE_GENERIC;
+                } else if (match_option(arg, ret, "auto")) {
+                        return SPECTRE_V2_CMD_AUTO;
+                }
+        }
+
+        if (!cmdline_find_option_bool(boot_command_line, "nospectre_v2"))
+                return SPECTRE_V2_CMD_AUTO;
+disable:
+        spec2_print_if_insecure("disabled on command line.");
+        return SPECTRE_V2_CMD_NONE;
+}
+
+/* Check for Skylake-like CPUs (for RSB handling) */
+static bool __init is_skylake_era(void)
+{
+        if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
+            boot_cpu_data.x86 == 6) {
+                switch (boot_cpu_data.x86_model) {
+                case INTEL_FAM6_SKYLAKE_MOBILE:
+                case INTEL_FAM6_SKYLAKE_DESKTOP:
+                case INTEL_FAM6_SKYLAKE_X:
+                case INTEL_FAM6_KABYLAKE_MOBILE:
+                case INTEL_FAM6_KABYLAKE_DESKTOP:
+                        return true;
+                }
+        }
+        return false;
+}
+
+static void __init spectre_v2_select_mitigation(void)
+{
+        enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
+        enum spectre_v2_mitigation mode = SPECTRE_V2_NONE;
+
+        /*
+         * If the CPU is not affected and the command line mode is NONE or AUTO
+         * then nothing to do.
+         */
+        if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2) &&
+            (cmd == SPECTRE_V2_CMD_NONE || cmd == SPECTRE_V2_CMD_AUTO))
+                return;
+
+        switch (cmd) {
+        case SPECTRE_V2_CMD_NONE:
+                return;
+
+        case SPECTRE_V2_CMD_FORCE:
+                /* FALLTRHU */
+        case SPECTRE_V2_CMD_AUTO:
+                goto retpoline_auto;
+
+        case SPECTRE_V2_CMD_RETPOLINE_AMD:
+                if (IS_ENABLED(CONFIG_RETPOLINE))
+                        goto retpoline_amd;
+                break;
+        case SPECTRE_V2_CMD_RETPOLINE_GENERIC:
+                if (IS_ENABLED(CONFIG_RETPOLINE))
+                        goto retpoline_generic;
+                break;
+        case SPECTRE_V2_CMD_RETPOLINE:
+                if (IS_ENABLED(CONFIG_RETPOLINE))
+                        goto retpoline_auto;
+                break;
+        }
+        pr_err("kernel not compiled with retpoline; no mitigation available!");
+        return;
+
+retpoline_auto:
+        if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
+        retpoline_amd:
+                if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
+                        pr_err("LFENCE not serializing. Switching to generic retpoline\n");
+                        goto retpoline_generic;
+                }
+                mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_AMD :
+                                         SPECTRE_V2_RETPOLINE_MINIMAL_AMD;
+                setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
+                setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
+        } else {
+        retpoline_generic:
+                mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_GENERIC :
+                                         SPECTRE_V2_RETPOLINE_MINIMAL;
+                setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
+        }
+
+        spectre_v2_enabled = mode;
+        pr_info("%s\n", spectre_v2_strings[mode]);
+
+        /*
+         * If neither SMEP or KPTI are available, there is a risk of
+         * hitting userspace addresses in the RSB after a context switch
+         * from a shallow call stack to a deeper one. To prevent this fill
+         * the entire RSB, even when using IBRS.
+         *
+         * Skylake era CPUs have a separate issue with *underflow* of the
+         * RSB, when they will predict 'ret' targets from the generic BTB.
+         * The proper mitigation for this is IBRS. If IBRS is not supported
+         * or deactivated in favour of retpolines the RSB fill on context
+         * switch is required.
+         */
+        if ((!boot_cpu_has(X86_FEATURE_PTI) &&
+             !boot_cpu_has(X86_FEATURE_SMEP)) || is_skylake_era()) {
+                setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
+                pr_info("Filling RSB on context switch\n");
+        }
+}
+
+#undef pr_fmt
+
+#ifdef CONFIG_SYSFS
+ssize_t cpu_show_meltdown(struct device *dev,
+                          struct device_attribute *attr, char *buf)
+{
+        if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
+                return sprintf(buf, "Not affected\n");
+        if (boot_cpu_has(X86_FEATURE_PTI))
+                return sprintf(buf, "Mitigation: PTI\n");
+        return sprintf(buf, "Vulnerable\n");
+}
+
+ssize_t cpu_show_spectre_v1(struct device *dev,
+                            struct device_attribute *attr, char *buf)
+{
+        if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1))
+                return sprintf(buf, "Not affected\n");
+        return sprintf(buf, "Vulnerable\n");
+}
+
+ssize_t cpu_show_spectre_v2(struct device *dev,
+                            struct device_attribute *attr, char *buf)
+{
+        if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
+                return sprintf(buf, "Not affected\n");
+
+        return sprintf(buf, "%s\n", spectre_v2_strings[spectre_v2_enabled]);
+}
+#endif