x86/speculation: Add command line control for indirect branch speculation

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

// SPDX-License-Identifier: GPL-2.0
/*
 *  Copyright (C) 1994  Linus Torvalds
 *
 *  Cyrix stuff, June 1998 by:
 *      - Rafael R. Reilova (moved everything from head.S),
 *        <rreilova@ececs.uc.edu>
 *      - Channing Corn (tests & fixes),
 *      - Andrew D. Balsa (code cleanup).
 */
#include <linux/init.h>
#include <linux/utsname.h>
#include <linux/cpu.h>
#include <linux/module.h>
#include <linux/nospec.h>
#include <linux/prctl.h>
#include <linux/sched/smt.h>

#include <asm/spec-ctrl.h>
#include <asm/cmdline.h>
#include <asm/bugs.h>
#include <asm/processor.h>
#include <asm/processor-flags.h>
#include <asm/fpu/internal.h>
#include <asm/msr.h>
#include <asm/vmx.h>
#include <asm/paravirt.h>
#include <asm/alternative.h>
#include <asm/pgtable.h>
#include <asm/set_memory.h>
#include <asm/intel-family.h>
#include <asm/e820/api.h>

static void __init spectre_v2_select_mitigation(void);
static void __init ssb_select_mitigation(void);
static void __init l1tf_select_mitigation(void);

/* The base value of the SPEC_CTRL MSR that always has to be preserved. */
u64 x86_spec_ctrl_base;
EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);
static DEFINE_MUTEX(spec_ctrl_mutex);

/*
 * The vendor and possibly platform specific bits which can be modified in
 * x86_spec_ctrl_base.
 */
static u64 __ro_after_init x86_spec_ctrl_mask = SPEC_CTRL_IBRS;

/*
 * AMD specific MSR info for Speculative Store Bypass control.
 * x86_amd_ls_cfg_ssbd_mask is initialized in identify_boot_cpu().
 */
u64 __ro_after_init x86_amd_ls_cfg_base;
u64 __ro_after_init x86_amd_ls_cfg_ssbd_mask;

/* Control conditional STIPB in switch_to() */
DEFINE_STATIC_KEY_FALSE(switch_to_cond_stibp);

void __init check_bugs(void)
{
        identify_boot_cpu();

        /*
         * identify_boot_cpu() initialized SMT support information, let the
         * core code know.
         */
        cpu_smt_check_topology_early();

        if (!IS_ENABLED(CONFIG_SMP)) {
                pr_info("CPU: ");
                print_cpu_info(&boot_cpu_data);
        }

        /*
         * Read the SPEC_CTRL MSR to account for reserved bits which may
         * have unknown values. AMD64_LS_CFG MSR is cached in the early AMD
         * init code as it is not enumerated and depends on the family.
         */
        if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
                rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);

        /* Allow STIBP in MSR_SPEC_CTRL if supported */
        if (boot_cpu_has(X86_FEATURE_STIBP))
                x86_spec_ctrl_mask |= SPEC_CTRL_STIBP;

        /* 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();

        l1tf_select_mitigation();

#ifdef CONFIG_X86_32
        /*
         * Check whether we are able to run this kernel safely on SMP.
         *
         * - i386 is no longer supported.
         * - In order to run on anything without a TSC, we need to be
         *   compiled for a i486.
         */
        if (boot_cpu_data.x86 < 4)
                panic("Kernel requires i486+ for 'invlpg' and other features");

        init_utsname()->machine[1] =
                '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
        alternative_instructions();

        fpu__init_check_bugs();
#else /* CONFIG_X86_64 */
        alternative_instructions();

        /*
         * Make sure the first 2MB area is not mapped by huge pages
         * There are typically fixed size MTRRs in there and overlapping
         * MTRRs into large pages causes slow downs.
         *
         * Right now we don't do that with gbpages because there seems
         * very little benefit for that case.
         */
        if (!direct_gbpages)
                set_memory_4k((unsigned long)__va(0), 1);
#endif
}

void
x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
{
        u64 msrval, guestval, hostval = x86_spec_ctrl_base;
        struct thread_info *ti = current_thread_info();

        /* Is MSR_SPEC_CTRL implemented ? */
        if (static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) {
                /*
                 * Restrict guest_spec_ctrl to supported values. Clear the
                 * modifiable bits in the host base value and or the
                 * modifiable bits from the guest value.
                 */
                guestval = hostval & ~x86_spec_ctrl_mask;
                guestval |= guest_spec_ctrl & x86_spec_ctrl_mask;

                /* SSBD controlled in MSR_SPEC_CTRL */
                if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
                    static_cpu_has(X86_FEATURE_AMD_SSBD))
                        hostval |= ssbd_tif_to_spec_ctrl(ti->flags);

                if (hostval != guestval) {
                        msrval = setguest ? guestval : hostval;
                        wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
                }
        }

        /*
         * If SSBD is not handled in MSR_SPEC_CTRL on AMD, update
         * MSR_AMD64_L2_CFG or MSR_VIRT_SPEC_CTRL if supported.
         */
        if (!static_cpu_has(X86_FEATURE_LS_CFG_SSBD) &&
            !static_cpu_has(X86_FEATURE_VIRT_SSBD))
                return;

        /*
         * If the host has SSBD mitigation enabled, force it in the host's
         * virtual MSR value. If its not permanently enabled, evaluate
         * current's TIF_SSBD thread flag.
         */
        if (static_cpu_has(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE))
                hostval = SPEC_CTRL_SSBD;
        else
                hostval = ssbd_tif_to_spec_ctrl(ti->flags);

        /* Sanitize the guest value */
        guestval = guest_virt_spec_ctrl & SPEC_CTRL_SSBD;

        if (hostval != guestval) {
                unsigned long tif;

                tif = setguest ? ssbd_spec_ctrl_to_tif(guestval) :
                                 ssbd_spec_ctrl_to_tif(hostval);

                speculation_ctrl_update(tif);
        }
}
EXPORT_SYMBOL_GPL(x86_virt_spec_ctrl);

static void x86_amd_ssb_disable(void)
{
        u64 msrval = x86_amd_ls_cfg_base | x86_amd_ls_cfg_ssbd_mask;

        if (boot_cpu_has(X86_FEATURE_VIRT_SSBD))
                wrmsrl(MSR_AMD64_VIRT_SPEC_CTRL, SPEC_CTRL_SSBD);
        else if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD))
                wrmsrl(MSR_AMD64_LS_CFG, msrval);
}

#undef pr_fmt
#define pr_fmt(fmt)     "Spectre V2 : " fmt

static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =
        SPECTRE_V2_NONE;

static enum spectre_v2_user_mitigation spectre_v2_user __ro_after_init =
        SPECTRE_V2_USER_NONE;

#ifdef RETPOLINE
static bool spectre_v2_bad_module;

bool retpoline_module_ok(bool has_retpoline)
{
        if (spectre_v2_enabled == SPECTRE_V2_NONE || has_retpoline)
                return true;

        pr_err("System may be vulnerable to spectre v2\n");
        spectre_v2_bad_module = true;
        return false;
}

static inline const char *spectre_v2_module_string(void)
{
        return spectre_v2_bad_module ? " - vulnerable module loaded" : "";
}
#else
static inline const char *spectre_v2_module_string(void) { return ""; }
#endif

static inline bool match_option(const char *arg, int arglen, const char *opt)
{
        int len = strlen(opt);

        return len == arglen && !strncmp(arg, opt, len);
}

/* The kernel command line selection for spectre v2 */
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,
};

enum spectre_v2_user_cmd {
        SPECTRE_V2_USER_CMD_NONE,
        SPECTRE_V2_USER_CMD_AUTO,
        SPECTRE_V2_USER_CMD_FORCE,
};

static const char * const spectre_v2_user_strings[] = {
        [SPECTRE_V2_USER_NONE]          = "User space: Vulnerable",
        [SPECTRE_V2_USER_STRICT]        = "User space: Mitigation: STIBP protection",
};

static const struct {
        const char                      *option;
        enum spectre_v2_user_cmd        cmd;
        bool                            secure;
} v2_user_options[] __initdata = {
        { "auto",       SPECTRE_V2_USER_CMD_AUTO,       false },
        { "off",        SPECTRE_V2_USER_CMD_NONE,       false },
        { "on",         SPECTRE_V2_USER_CMD_FORCE,      true  },
};

static void __init spec_v2_user_print_cond(const char *reason, bool secure)
{
        if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) != secure)
                pr_info("spectre_v2_user=%s forced on command line.\n", reason);
}

static enum spectre_v2_user_cmd __init
spectre_v2_parse_user_cmdline(enum spectre_v2_mitigation_cmd v2_cmd)
{
        char arg[20];
        int ret, i;

        switch (v2_cmd) {
        case SPECTRE_V2_CMD_NONE:
                return SPECTRE_V2_USER_CMD_NONE;
        case SPECTRE_V2_CMD_FORCE:
                return SPECTRE_V2_USER_CMD_FORCE;
        default:
                break;
        }

        ret = cmdline_find_option(boot_command_line, "spectre_v2_user",
                                  arg, sizeof(arg));
        if (ret < 0)
                return SPECTRE_V2_USER_CMD_AUTO;

        for (i = 0; i < ARRAY_SIZE(v2_user_options); i++) {
                if (match_option(arg, ret, v2_user_options[i].option)) {
                        spec_v2_user_print_cond(v2_user_options[i].option,
                                                v2_user_options[i].secure);
                        return v2_user_options[i].cmd;
                }
        }

        pr_err("Unknown user space protection option (%s). Switching to AUTO select\n", arg);
        return SPECTRE_V2_USER_CMD_AUTO;
}

static void __init
spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
{
        enum spectre_v2_user_mitigation mode = SPECTRE_V2_USER_NONE;
        bool smt_possible = IS_ENABLED(CONFIG_SMP);

        if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP))
                return;

        if (cpu_smt_control == CPU_SMT_FORCE_DISABLED ||
            cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
                smt_possible = false;

        switch (spectre_v2_parse_user_cmdline(v2_cmd)) {
        case SPECTRE_V2_USER_CMD_AUTO:
        case SPECTRE_V2_USER_CMD_NONE:
                goto set_mode;
        case SPECTRE_V2_USER_CMD_FORCE:
                mode = SPECTRE_V2_USER_STRICT;
                break;
        }

        /* Initialize Indirect Branch Prediction Barrier */
        if (boot_cpu_has(X86_FEATURE_IBPB)) {
                setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
                pr_info("Spectre v2 mitigation: Enabling Indirect Branch Prediction Barrier\n");
        }

        /* If enhanced IBRS is enabled no STIPB required */
        if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
                return;

set_mode:
        spectre_v2_user = mode;
        /* Only print the STIBP mode when SMT possible */
        if (smt_possible)
                pr_info("%s\n", spectre_v2_user_strings[mode]);
}

static const char * const spectre_v2_strings[] = {
        [SPECTRE_V2_NONE]                       = "Vulnerable",
        [SPECTRE_V2_RETPOLINE_GENERIC]          = "Mitigation: Full generic retpoline",
        [SPECTRE_V2_RETPOLINE_AMD]              = "Mitigation: Full AMD retpoline",
        [SPECTRE_V2_IBRS_ENHANCED]              = "Mitigation: Enhanced IBRS",
};

static const struct {
        const char *option;
        enum spectre_v2_mitigation_cmd cmd;
        bool secure;
} mitigation_options[] __initdata = {
        { "off",                SPECTRE_V2_CMD_NONE,              false },
        { "on",                 SPECTRE_V2_CMD_FORCE,             true  },
        { "retpoline",          SPECTRE_V2_CMD_RETPOLINE,         false },
        { "retpoline,amd",      SPECTRE_V2_CMD_RETPOLINE_AMD,     false },
        { "retpoline,generic",  SPECTRE_V2_CMD_RETPOLINE_GENERIC, false },
        { "auto",               SPECTRE_V2_CMD_AUTO,              false },
};

static void __init spec_v2_print_cond(const char *reason, bool secure)
{
        if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) != secure)
                pr_info("%s selected on command line.\n", reason);
}

static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
{
        enum spectre_v2_mitigation_cmd cmd = SPECTRE_V2_CMD_AUTO;
        char arg[20];
        int ret, i;

        if (cmdline_find_option_bool(boot_command_line, "nospectre_v2"))
                return SPECTRE_V2_CMD_NONE;

        ret = cmdline_find_option(boot_command_line, "spectre_v2", arg, sizeof(arg));
        if (ret < 0)
                return SPECTRE_V2_CMD_AUTO;

        for (i = 0; i < ARRAY_SIZE(mitigation_options); i++) {
                if (!match_option(arg, ret, mitigation_options[i].option))
                        continue;
                cmd = mitigation_options[i].cmd;
                break;
        }

        if (i >= ARRAY_SIZE(mitigation_options)) {
                pr_err("unknown option (%s). Switching to AUTO select\n", arg);
                return SPECTRE_V2_CMD_AUTO;
        }

        if ((cmd == SPECTRE_V2_CMD_RETPOLINE ||
             cmd == SPECTRE_V2_CMD_RETPOLINE_AMD ||
             cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC) &&
            !IS_ENABLED(CONFIG_RETPOLINE)) {
                pr_err("%s selected but not compiled in. Switching to AUTO select\n", mitigation_options[i].option);
                return SPECTRE_V2_CMD_AUTO;
        }

        if (cmd == SPECTRE_V2_CMD_RETPOLINE_AMD &&
            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;
        }

        spec_v2_print_cond(mitigation_options[i].option,
                           mitigation_options[i].secure);
        return cmd;
}

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:
        case SPECTRE_V2_CMD_AUTO:
                if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) {
                        mode = SPECTRE_V2_IBRS_ENHANCED;
                        /* Force it so VMEXIT will restore correctly */
                        x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
                        wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
                        goto specv2_set_mode;
                }
                if (IS_ENABLED(CONFIG_RETPOLINE))
                        goto retpoline_auto;
                break;
        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("Spectre mitigation: 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("Spectre mitigation: LFENCE not serializing, switching to generic retpoline\n");
                        goto retpoline_generic;
                }
                mode = SPECTRE_V2_RETPOLINE_AMD;
                setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
                setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
        } else {
        retpoline_generic:
                mode = SPECTRE_V2_RETPOLINE_GENERIC;
                setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
        }

specv2_set_mode:
        spectre_v2_enabled = mode;
        pr_info("%s\n", spectre_v2_strings[mode]);

        /*
         * If spectre v2 protection has been enabled, unconditionally fill
         * RSB during a context switch; this protects against two independent
         * issues:
         *
         *      - RSB underflow (and switch to BTB) on Skylake+
         *      - SpectreRSB variant of spectre v2 on X86_BUG_SPECTRE_V2 CPUs
         */
        setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
        pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n");

        /*
         * Retpoline means the kernel is safe because it has no indirect
         * branches. Enhanced IBRS protects firmware too, so, enable restricted
         * speculation around firmware calls only when Enhanced IBRS isn't
         * supported.
         *
         * Use "mode" to check Enhanced IBRS instead of boot_cpu_has(), because
         * the user might select retpoline on the kernel command line and if
         * the CPU supports Enhanced IBRS, kernel might un-intentionally not
         * enable IBRS around firmware calls.
         */
        if (boot_cpu_has(X86_FEATURE_IBRS) && mode != SPECTRE_V2_IBRS_ENHANCED) {
                setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
                pr_info("Enabling Restricted Speculation for firmware calls\n");
        }

        /* Set up IBPB and STIBP depending on the general spectre V2 command */
        spectre_v2_user_select_mitigation(cmd);

        /* Enable STIBP if appropriate */
        arch_smt_update();
}

static bool stibp_needed(void)
{
        /* Enhanced IBRS makes using STIBP unnecessary. */
        if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
                return false;

        /* Check for strict user mitigation mode */
        return spectre_v2_user == SPECTRE_V2_USER_STRICT;
}

static void update_stibp_msr(void *info)
{
        wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
}

void arch_smt_update(void)
{
        u64 mask;

        if (!stibp_needed())
                return;

        mutex_lock(&spec_ctrl_mutex);

        mask = x86_spec_ctrl_base & ~SPEC_CTRL_STIBP;
        if (sched_smt_active())
                mask |= SPEC_CTRL_STIBP;

        if (mask != x86_spec_ctrl_base) {
                pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n",
                        mask & SPEC_CTRL_STIBP ? "Enabling" : "Disabling");
                x86_spec_ctrl_base = mask;
                on_each_cpu(update_stibp_msr, NULL, 1);
        }
        mutex_unlock(&spec_ctrl_mutex);
}

#undef pr_fmt
#define pr_fmt(fmt)     "Speculative Store Bypass: " fmt

static enum ssb_mitigation ssb_mode __ro_after_init = 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,
        SPEC_STORE_BYPASS_CMD_PRCTL,
        SPEC_STORE_BYPASS_CMD_SECCOMP,
};

static const char * const ssb_strings[] = {
        [SPEC_STORE_BYPASS_NONE]        = "Vulnerable",
        [SPEC_STORE_BYPASS_DISABLE]     = "Mitigation: Speculative Store Bypass disabled",
        [SPEC_STORE_BYPASS_PRCTL]       = "Mitigation: Speculative Store Bypass disabled via prctl",
        [SPEC_STORE_BYPASS_SECCOMP]     = "Mitigation: Speculative Store Bypass disabled via prctl and seccomp",
};

static const struct {
        const char *option;
        enum ssb_mitigation_cmd cmd;
} ssb_mitigation_options[]  __initdata = {
        { "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 */
        { "prctl",      SPEC_STORE_BYPASS_CMD_PRCTL },   /* Disable Speculative Store Bypass via prctl */
        { "seccomp",    SPEC_STORE_BYPASS_CMD_SECCOMP }, /* Disable Speculative Store Bypass via prctl and seccomp */
};

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 __init __ssb_select_mitigation(void)
{
        enum ssb_mitigation mode = SPEC_STORE_BYPASS_NONE;
        enum ssb_mitigation_cmd cmd;

        if (!boot_cpu_has(X86_FEATURE_SSBD))
                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_SECCOMP:
                /*
                 * Choose prctl+seccomp as the default mode if seccomp is
                 * enabled.
                 */
                if (IS_ENABLED(CONFIG_SECCOMP))
                        mode = SPEC_STORE_BYPASS_SECCOMP;
                else
                        mode = SPEC_STORE_BYPASS_PRCTL;
                break;
        case SPEC_STORE_BYPASS_CMD_ON:
                mode = SPEC_STORE_BYPASS_DISABLE;
                break;
        case SPEC_STORE_BYPASS_CMD_PRCTL:
                mode = SPEC_STORE_BYPASS_PRCTL;
                break;
        case SPEC_STORE_BYPASS_CMD_NONE:
                break;
        }

        /*
         * We have three CPU feature flags that are in play here:
         *  - X86_BUG_SPEC_STORE_BYPASS - CPU is susceptible.
         *  - X86_FEATURE_SSBD - CPU is able to turn off speculative store bypass
         *  - X86_FEATURE_SPEC_STORE_BYPASS_DISABLE - engage the mitigation
         */
        if (mode == SPEC_STORE_BYPASS_DISABLE) {
                setup_force_cpu_cap(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE);
                /*
                 * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may
                 * use a completely different MSR and bit dependent on family.
                 */
                if (!static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) &&
                    !static_cpu_has(X86_FEATURE_AMD_SSBD)) {
                        x86_amd_ssb_disable();
                } else {
                        x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
                        x86_spec_ctrl_mask |= SPEC_CTRL_SSBD;
                        wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
                }
        }

        return mode;
}

static void ssb_select_mitigation(void)
{
        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
#define pr_fmt(fmt)     "Speculation prctl: " fmt

static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
{
        bool update;

        if (ssb_mode != SPEC_STORE_BYPASS_PRCTL &&
            ssb_mode != SPEC_STORE_BYPASS_SECCOMP)
                return -ENXIO;

        switch (ctrl) {
        case PR_SPEC_ENABLE:
                /* If speculation is force disabled, enable is not allowed */
                if (task_spec_ssb_force_disable(task))
                        return -EPERM;
                task_clear_spec_ssb_disable(task);
                update = test_and_clear_tsk_thread_flag(task, TIF_SSBD);
                break;
        case PR_SPEC_DISABLE:
                task_set_spec_ssb_disable(task);
                update = !test_and_set_tsk_thread_flag(task, TIF_SSBD);
                break;
        case PR_SPEC_FORCE_DISABLE:
                task_set_spec_ssb_disable(task);
                task_set_spec_ssb_force_disable(task);
                update = !test_and_set_tsk_thread_flag(task, TIF_SSBD);
                break;
        default:
                return -ERANGE;
        }

        /*
         * If being set on non-current task, delay setting the CPU
         * mitigation until it is next scheduled.
         */
        if (task == current && update)
                speculation_ctrl_update_current();

        return 0;
}

int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
                             unsigned long ctrl)
{
        switch (which) {
        case PR_SPEC_STORE_BYPASS:
                return ssb_prctl_set(task, ctrl);
        default:
                return -ENODEV;
        }
}

#ifdef CONFIG_SECCOMP
void arch_seccomp_spec_mitigate(struct task_struct *task)
{
        if (ssb_mode == SPEC_STORE_BYPASS_SECCOMP)
                ssb_prctl_set(task, PR_SPEC_FORCE_DISABLE);
}
#endif

static int ssb_prctl_get(struct task_struct *task)
{
        switch (ssb_mode) {
        case SPEC_STORE_BYPASS_DISABLE:
                return PR_SPEC_DISABLE;
        case SPEC_STORE_BYPASS_SECCOMP:
        case SPEC_STORE_BYPASS_PRCTL:
                if (task_spec_ssb_force_disable(task))
                        return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
                if (task_spec_ssb_disable(task))
                        return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
                return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
        default:
                if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS))
                        return PR_SPEC_ENABLE;
                return PR_SPEC_NOT_AFFECTED;
        }
}

int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
{
        switch (which) {
        case PR_SPEC_STORE_BYPASS:
                return ssb_prctl_get(task);
        default:
                return -ENODEV;
        }
}

void x86_spec_ctrl_setup_ap(void)
{
        if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
                wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);

        if (ssb_mode == SPEC_STORE_BYPASS_DISABLE)
                x86_amd_ssb_disable();
}

#undef pr_fmt
#define pr_fmt(fmt)     "L1TF: " fmt

/* Default mitigation for L1TF-affected CPUs */
enum l1tf_mitigations l1tf_mitigation __ro_after_init = L1TF_MITIGATION_FLUSH;
#if IS_ENABLED(CONFIG_KVM_INTEL)
EXPORT_SYMBOL_GPL(l1tf_mitigation);

enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation);
#endif

/*
 * These CPUs all support 44bits physical address space internally in the
 * cache but CPUID can report a smaller number of physical address bits.
 *
 * The L1TF mitigation uses the top most address bit for the inversion of
 * non present PTEs. When the installed memory reaches into the top most
 * address bit due to memory holes, which has been observed on machines
 * which report 36bits physical address bits and have 32G RAM installed,
 * then the mitigation range check in l1tf_select_mitigation() triggers.
 * This is a false positive because the mitigation is still possible due to
 * the fact that the cache uses 44bit internally. Use the cache bits
 * instead of the reported physical bits and adjust them on the affected
 * machines to 44bit if the reported bits are less than 44.
 */
static void override_cache_bits(struct cpuinfo_x86 *c)
{
        if (c->x86 != 6)
                return;

        switch (c->x86_model) {
        case INTEL_FAM6_NEHALEM:
        case INTEL_FAM6_WESTMERE:
        case INTEL_FAM6_SANDYBRIDGE:
        case INTEL_FAM6_IVYBRIDGE:
        case INTEL_FAM6_HASWELL_CORE:
        case INTEL_FAM6_HASWELL_ULT:
        case INTEL_FAM6_HASWELL_GT3E:
        case INTEL_FAM6_BROADWELL_CORE:
        case INTEL_FAM6_BROADWELL_GT3E:
        case INTEL_FAM6_SKYLAKE_MOBILE:
        case INTEL_FAM6_SKYLAKE_DESKTOP:
        case INTEL_FAM6_KABYLAKE_MOBILE:
        case INTEL_FAM6_KABYLAKE_DESKTOP:
                if (c->x86_cache_bits < 44)
                        c->x86_cache_bits = 44;
                break;
        }
}

static void __init l1tf_select_mitigation(void)
{
        u64 half_pa;

        if (!boot_cpu_has_bug(X86_BUG_L1TF))
                return;

        override_cache_bits(&boot_cpu_data);

        switch (l1tf_mitigation) {
        case L1TF_MITIGATION_OFF:
        case L1TF_MITIGATION_FLUSH_NOWARN:
        case L1TF_MITIGATION_FLUSH:
                break;
        case L1TF_MITIGATION_FLUSH_NOSMT:
        case L1TF_MITIGATION_FULL:
                cpu_smt_disable(false);
                break;
        case L1TF_MITIGATION_FULL_FORCE:
                cpu_smt_disable(true);
                break;
        }

#if CONFIG_PGTABLE_LEVELS == 2
        pr_warn("Kernel not compiled for PAE. No mitigation for L1TF\n");
        return;
#endif

        half_pa = (u64)l1tf_pfn_limit() << PAGE_SHIFT;
        if (e820__mapped_any(half_pa, ULLONG_MAX - half_pa, E820_TYPE_RAM)) {
                pr_warn("System has more than MAX_PA/2 memory. L1TF mitigation not effective.\n");
                return;
        }

        setup_force_cpu_cap(X86_FEATURE_L1TF_PTEINV);
}

static int __init l1tf_cmdline(char *str)
{
        if (!boot_cpu_has_bug(X86_BUG_L1TF))
                return 0;

        if (!str)
                return -EINVAL;

        if (!strcmp(str, "off"))
                l1tf_mitigation = L1TF_MITIGATION_OFF;
        else if (!strcmp(str, "flush,nowarn"))
                l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOWARN;
        else if (!strcmp(str, "flush"))
                l1tf_mitigation = L1TF_MITIGATION_FLUSH;
        else if (!strcmp(str, "flush,nosmt"))
                l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;
        else if (!strcmp(str, "full"))
                l1tf_mitigation = L1TF_MITIGATION_FULL;
        else if (!strcmp(str, "full,force"))
                l1tf_mitigation = L1TF_MITIGATION_FULL_FORCE;

        return 0;
}
early_param("l1tf", l1tf_cmdline);

#undef pr_fmt

#ifdef CONFIG_SYSFS

#define L1TF_DEFAULT_MSG "Mitigation: PTE Inversion"

#if IS_ENABLED(CONFIG_KVM_INTEL)
static const char * const l1tf_vmx_states[] = {
        [VMENTER_L1D_FLUSH_AUTO]                = "auto",
        [VMENTER_L1D_FLUSH_NEVER]               = "vulnerable",
        [VMENTER_L1D_FLUSH_COND]                = "conditional cache flushes",
        [VMENTER_L1D_FLUSH_ALWAYS]              = "cache flushes",
        [VMENTER_L1D_FLUSH_EPT_DISABLED]        = "EPT disabled",
        [VMENTER_L1D_FLUSH_NOT_REQUIRED]        = "flush not necessary"
};

static ssize_t l1tf_show_state(char *buf)
{
        if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_AUTO)
                return sprintf(buf, "%s\n", L1TF_DEFAULT_MSG);

        if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_EPT_DISABLED ||
            (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_NEVER &&
             sched_smt_active())) {
                return sprintf(buf, "%s; VMX: %s\n", L1TF_DEFAULT_MSG,
                               l1tf_vmx_states[l1tf_vmx_mitigation]);
        }

        return sprintf(buf, "%s; VMX: %s, SMT %s\n", L1TF_DEFAULT_MSG,
                       l1tf_vmx_states[l1tf_vmx_mitigation],
                       sched_smt_active() ? "vulnerable" : "disabled");
}
#else
static ssize_t l1tf_show_state(char *buf)
{
        return sprintf(buf, "%s\n", L1TF_DEFAULT_MSG);
}
#endif

static char *stibp_state(void)
{
        if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
                return "";

        switch (spectre_v2_user) {
        case SPECTRE_V2_USER_NONE:
                return ", STIBP: disabled";
        case SPECTRE_V2_USER_STRICT:
                return ", STIBP: forced";
        }
        return "";
}

static char *ibpb_state(void)
{
        if (boot_cpu_has(X86_FEATURE_USE_IBPB))
                return ", IBPB";
        else
                return "";
}

static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
                               char *buf, unsigned int bug)
{
        if (!boot_cpu_has_bug(bug))
                return sprintf(buf, "Not affected\n");

        switch (bug) {
        case X86_BUG_CPU_MELTDOWN:
                if (boot_cpu_has(X86_FEATURE_PTI))
                        return sprintf(buf, "Mitigation: PTI\n");

                break;

        case X86_BUG_SPECTRE_V1:
                return sprintf(buf, "Mitigation: __user pointer sanitization\n");

        case X86_BUG_SPECTRE_V2:
                return sprintf(buf, "%s%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
                               ibpb_state(),
                               boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "",
                               stibp_state(),
                               boot_cpu_has(X86_FEATURE_RSB_CTXSW) ? ", RSB filling" : "",
                               spectre_v2_module_string());

        case X86_BUG_SPEC_STORE_BYPASS:
                return sprintf(buf, "%s\n", ssb_strings[ssb_mode]);

        case X86_BUG_L1TF:
                if (boot_cpu_has(X86_FEATURE_L1TF_PTEINV))
                        return l1tf_show_state(buf);
                break;
        default:
                break;
        }

        return sprintf(buf, "Vulnerable\n");
}

ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf)
{
        return cpu_show_common(dev, attr, buf, X86_BUG_CPU_MELTDOWN);
}

ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr, char *buf)
{
        return cpu_show_common(dev, attr, buf, X86_BUG_SPECTRE_V1);
}

ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf)
{
        return cpu_show_common(dev, attr, buf, X86_BUG_SPECTRE_V2);
}

ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute *attr, char *buf)
{
        return cpu_show_common(dev, attr, buf, X86_BUG_SPEC_STORE_BYPASS);
}

ssize_t cpu_show_l1tf(struct device *dev, struct device_attribute *attr, char *buf)
{
        return cpu_show_common(dev, attr, buf, X86_BUG_L1TF);
}
#endif