// SPDX-License-Identifier: GPL-2.0
#include <linux/module.h>
#include <linux/device.h>
#include <linux/cpu.h>
#include <asm/nospec-branch.h>

int nobp = IS_ENABLED(CONFIG_KERNEL_NOBP);

static int __init nobp_setup_early(char *str)
{
        bool enabled;
        int rc;

        rc = kstrtobool(str, &enabled);
        if (rc)
                return rc;
        if (enabled && test_facility(82)) {
                /*
                 * The user explicitly requested nobp=1, enable it and
                 * disable the expoline support.
                 */
                nobp = 1;
                if (IS_ENABLED(CONFIG_EXPOLINE))
                        nospec_disable = 1;
        } else {
                nobp = 0;
        }
        return 0;
}
early_param("nobp", nobp_setup_early);

static int __init nospec_setup_early(char *str)
{
        nobp = 0;
        return 0;
}
early_param("nospec", nospec_setup_early);

static int __init nospec_report(void)
{
        if (test_facility(156))
                pr_info("Spectre V2 mitigation: etokens\n");
        if (nospec_uses_trampoline())
                pr_info("Spectre V2 mitigation: execute trampolines\n");
        if (nobp_enabled())
                pr_info("Spectre V2 mitigation: limited branch prediction\n");
        return 0;
}
arch_initcall(nospec_report);

#ifdef CONFIG_EXPOLINE

int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);

static int __init nospectre_v2_setup_early(char *str)
{
        nospec_disable = 1;
        return 0;
}
early_param("nospectre_v2", nospectre_v2_setup_early);

void __init nospec_auto_detect(void)
{
        if (test_facility(156) || cpu_mitigations_off()) {
                /*
                 * The machine supports etokens.
                 * Disable expolines and disable nobp.
                 */
                if (__is_defined(CC_USING_EXPOLINE))
                        nospec_disable = 1;
                nobp = 0;
        } else if (__is_defined(CC_USING_EXPOLINE)) {
                /*
                 * The kernel has been compiled with expolines.
                 * Keep expolines enabled and disable nobp.
                 */
                nospec_disable = 0;
                nobp = 0;
        }
        /*
         * If the kernel has not been compiled with expolines the
         * nobp setting decides what is done, this depends on the
         * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
         */
}

static int __init spectre_v2_setup_early(char *str)
{
        if (str && !strncmp(str, "on", 2)) {
                nospec_disable = 0;
                nobp = 0;
        }
        if (str && !strncmp(str, "off", 3))
                nospec_disable = 1;
        if (str && !strncmp(str, "auto", 4))
                nospec_auto_detect();
        return 0;
}
early_param("spectre_v2", spectre_v2_setup_early);

static void __init_or_module __nospec_revert(s32 *start, s32 *end)
{
        enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
        static const u8 branch[] = { 0x47, 0x00, 0x07, 0x00 };
        u8 *instr, *thunk, *br;
        u8 insnbuf[6];
        s32 *epo;

        /* Second part of the instruction replace is always a nop */
        memcpy(insnbuf + 2, branch, sizeof(branch));
        for (epo = start; epo < end; epo++) {
                instr = (u8 *) epo + *epo;
                if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
                        type = BRCL_EXPOLINE;   /* brcl instruction */
                else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
                        type = BRASL_EXPOLINE;  /* brasl instruction */
                else
                        continue;
                thunk = instr + (long)(*(int *)(instr + 2)) * 2;
                if (thunk[0] == 0xc6 && thunk[1] == 0x00)
                        /* exrl %r0,<target-br> */
                        br = thunk + (long)(*(int *)(thunk + 2)) * 2;
                else
                        continue;
                if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
                        continue;
                switch (type) {
                case BRCL_EXPOLINE:
                        /* brcl to thunk, replace with br + nop */
                        insnbuf[0] = br[0];
                        insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
                        break;
                case BRASL_EXPOLINE:
                        /* brasl to thunk, replace with basr + nop */
                        insnbuf[0] = 0x0d;
                        insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
                        break;
                }

                s390_kernel_write(instr, insnbuf, 6);
        }
}

void __init_or_module nospec_revert(s32 *start, s32 *end)
{
        if (nospec_disable)
                __nospec_revert(start, end);
}

extern s32 __nospec_call_start[], __nospec_call_end[];
extern s32 __nospec_return_start[], __nospec_return_end[];
void __init nospec_init_branches(void)
{
        nospec_revert(__nospec_call_start, __nospec_call_end);
        nospec_revert(__nospec_return_start, __nospec_return_end);
}

#endif /* CONFIG_EXPOLINE */