// SPDX-License-Identifier: GPL-2.0
/*
 * Early cpufeature override framework
 *
 * Copyright (C) 2020 Google LLC
 * Author: Marc Zyngier <maz@kernel.org>
 */

#include <linux/ctype.h>
#include <linux/kernel.h>
#include <linux/libfdt.h>

#include <asm/cacheflush.h>
#include <asm/cpufeature.h>
#include <asm/setup.h>

#define FTR_DESC_NAME_LEN       20
#define FTR_DESC_FIELD_LEN      10
#define FTR_ALIAS_NAME_LEN      30
#define FTR_ALIAS_OPTION_LEN    80

struct ftr_set_desc {
        char                            name[FTR_DESC_NAME_LEN];
        struct arm64_ftr_override       *override;
        struct {
                char                    name[FTR_DESC_FIELD_LEN];
                u8                      shift;
                bool                    (*filter)(u64 val);
        }                               fields[];
};

static bool __init mmfr1_vh_filter(u64 val)
{
        /*
         * If we ever reach this point while running VHE, we're
         * guaranteed to be on one of these funky, VHE-stuck CPUs. If
         * the user was trying to force nVHE on us, proceed with
         * attitude adjustment.
         */
        return !(is_kernel_in_hyp_mode() && val == 0);
}

static const struct ftr_set_desc mmfr1 __initconst = {
        .name           = "id_aa64mmfr1",
        .override       = &id_aa64mmfr1_override,
        .fields         = {
                { "vh", ID_AA64MMFR1_VHE_SHIFT, mmfr1_vh_filter },
                {}
        },
};

static const struct ftr_set_desc pfr1 __initconst = {
        .name           = "id_aa64pfr1",
        .override       = &id_aa64pfr1_override,
        .fields         = {
                { "bt", ID_AA64PFR1_BT_SHIFT },
                { "mte", ID_AA64PFR1_MTE_SHIFT},
                {}
        },
};

static const struct ftr_set_desc isar1 __initconst = {
        .name           = "id_aa64isar1",
        .override       = &id_aa64isar1_override,
        .fields         = {
                { "gpi", ID_AA64ISAR1_GPI_SHIFT },
                { "gpa", ID_AA64ISAR1_GPA_SHIFT },
                { "api", ID_AA64ISAR1_API_SHIFT },
                { "apa", ID_AA64ISAR1_APA_SHIFT },
                {}
        },
};

extern struct arm64_ftr_override kaslr_feature_override;

static const struct ftr_set_desc kaslr __initconst = {
        .name           = "kaslr",
#ifdef CONFIG_RANDOMIZE_BASE
        .override       = &kaslr_feature_override,
#endif
        .fields         = {
                { "disabled", 0 },
                {}
        },
};

static const struct ftr_set_desc * const regs[] __initconst = {
        &mmfr1,
        &pfr1,
        &isar1,
        &kaslr,
};

static const struct {
        char    alias[FTR_ALIAS_NAME_LEN];
        char    feature[FTR_ALIAS_OPTION_LEN];
} aliases[] __initconst = {
        { "kvm-arm.mode=nvhe",          "id_aa64mmfr1.vh=0" },
        { "kvm-arm.mode=protected",     "id_aa64mmfr1.vh=0" },
        { "arm64.nobti",                "id_aa64pfr1.bt=0" },
        { "arm64.nopauth",
          "id_aa64isar1.gpi=0 id_aa64isar1.gpa=0 "
          "id_aa64isar1.api=0 id_aa64isar1.apa=0"          },
        { "arm64.nomte",                "id_aa64pfr1.mte=0" },
        { "nokaslr",                    "kaslr.disabled=1" },
};

static int __init find_field(const char *cmdline,
                             const struct ftr_set_desc *reg, int f, u64 *v)
{
        char opt[FTR_DESC_NAME_LEN + FTR_DESC_FIELD_LEN + 2];
        int len;

        len = snprintf(opt, ARRAY_SIZE(opt), "%s.%s=",
                       reg->name, reg->fields[f].name);

        if (!parameqn(cmdline, opt, len))
                return -1;

        return kstrtou64(cmdline + len, 0, v);
}

static void __init match_options(const char *cmdline)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(regs); i++) {
                int f;

                if (!regs[i]->override)
                        continue;

                for (f = 0; strlen(regs[i]->fields[f].name); f++) {
                        u64 shift = regs[i]->fields[f].shift;
                        u64 mask = 0xfUL << shift;
                        u64 v;

                        if (find_field(cmdline, regs[i], f, &v))
                                continue;

                        /*
                         * If an override gets filtered out, advertise
                         * it by setting the value to 0xf, but
                         * clearing the mask... Yes, this is fragile.
                         */
                        if (regs[i]->fields[f].filter &&
                            !regs[i]->fields[f].filter(v)) {
                                regs[i]->override->val  |= mask;
                                regs[i]->override->mask &= ~mask;
                                continue;
                        }

                        regs[i]->override->val  &= ~mask;
                        regs[i]->override->val  |= (v << shift) & mask;
                        regs[i]->override->mask |= mask;

                        return;
                }
        }
}

static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
{
        do {
                char buf[256];
                size_t len;
                int i;

                cmdline = skip_spaces(cmdline);

                for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++);
                if (!len)
                        return;

                len = min(len, ARRAY_SIZE(buf) - 1);
                strncpy(buf, cmdline, len);
                buf[len] = 0;

                if (strcmp(buf, "--") == 0)
                        return;

                cmdline += len;

                match_options(buf);

                for (i = 0; parse_aliases && i < ARRAY_SIZE(aliases); i++)
                        if (parameq(buf, aliases[i].alias))
                                __parse_cmdline(aliases[i].feature, false);
        } while (1);
}

static __init const u8 *get_bootargs_cmdline(void)
{
        const u8 *prop;
        void *fdt;
        int node;

        fdt = get_early_fdt_ptr();
        if (!fdt)
                return NULL;

        node = fdt_path_offset(fdt, "/chosen");
        if (node < 0)
                return NULL;

        prop = fdt_getprop(fdt, node, "bootargs", NULL);
        if (!prop)
                return NULL;

        return strlen(prop) ? prop : NULL;
}

static __init void parse_cmdline(void)
{
        const u8 *prop = get_bootargs_cmdline();

        if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !prop)
                __parse_cmdline(CONFIG_CMDLINE, true);

        if (!IS_ENABLED(CONFIG_CMDLINE_FORCE) && prop)
                __parse_cmdline(prop, true);
}

/* Keep checkers quiet */
void init_feature_override(void);

asmlinkage void __init init_feature_override(void)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(regs); i++) {
                if (regs[i]->override) {
                        regs[i]->override->val  = 0;
                        regs[i]->override->mask = 0;
                }
        }

        parse_cmdline();

        for (i = 0; i < ARRAY_SIZE(regs); i++) {
                if (regs[i]->override)
                        dcache_clean_inval_poc((unsigned long)regs[i]->override,
                                            (unsigned long)regs[i]->override +
                                            sizeof(*regs[i]->override));
        }
}