linux/arch/arm64/kernel/idreg-override.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Early cpufeature override framework
   4 *
   5 * Copyright (C) 2020 Google LLC
   6 * Author: Marc Zyngier <maz@kernel.org>
   7 */
   8
   9#include <linux/ctype.h>
  10#include <linux/kernel.h>
  11#include <linux/libfdt.h>
  12
  13#include <asm/cacheflush.h>
  14#include <asm/cpufeature.h>
  15#include <asm/setup.h>
  16
  17#define FTR_DESC_NAME_LEN       20
  18#define FTR_DESC_FIELD_LEN      10
  19#define FTR_ALIAS_NAME_LEN      30
  20#define FTR_ALIAS_OPTION_LEN    80
  21
  22struct ftr_set_desc {
  23        char                            name[FTR_DESC_NAME_LEN];
  24        struct arm64_ftr_override       *override;
  25        struct {
  26                char                    name[FTR_DESC_FIELD_LEN];
  27                u8                      shift;
  28                bool                    (*filter)(u64 val);
  29        }                               fields[];
  30};
  31
  32static bool __init mmfr1_vh_filter(u64 val)
  33{
  34        /*
  35         * If we ever reach this point while running VHE, we're
  36         * guaranteed to be on one of these funky, VHE-stuck CPUs. If
  37         * the user was trying to force nVHE on us, proceed with
  38         * attitude adjustment.
  39         */
  40        return !(is_kernel_in_hyp_mode() && val == 0);
  41}
  42
  43static const struct ftr_set_desc mmfr1 __initconst = {
  44        .name           = "id_aa64mmfr1",
  45        .override       = &id_aa64mmfr1_override,
  46        .fields         = {
  47                { "vh", ID_AA64MMFR1_VHE_SHIFT, mmfr1_vh_filter },
  48                {}
  49        },
  50};
  51
  52static const struct ftr_set_desc pfr1 __initconst = {
  53        .name           = "id_aa64pfr1",
  54        .override       = &id_aa64pfr1_override,
  55        .fields         = {
  56                { "bt", ID_AA64PFR1_BT_SHIFT },
  57                {}
  58        },
  59};
  60
  61static const struct ftr_set_desc isar1 __initconst = {
  62        .name           = "id_aa64isar1",
  63        .override       = &id_aa64isar1_override,
  64        .fields         = {
  65                { "gpi", ID_AA64ISAR1_GPI_SHIFT },
  66                { "gpa", ID_AA64ISAR1_GPA_SHIFT },
  67                { "api", ID_AA64ISAR1_API_SHIFT },
  68                { "apa", ID_AA64ISAR1_APA_SHIFT },
  69                {}
  70        },
  71};
  72
  73extern struct arm64_ftr_override kaslr_feature_override;
  74
  75static const struct ftr_set_desc kaslr __initconst = {
  76        .name           = "kaslr",
  77#ifdef CONFIG_RANDOMIZE_BASE
  78        .override       = &kaslr_feature_override,
  79#endif
  80        .fields         = {
  81                { "disabled", 0 },
  82                {}
  83        },
  84};
  85
  86static const struct ftr_set_desc * const regs[] __initconst = {
  87        &mmfr1,
  88        &pfr1,
  89        &isar1,
  90        &kaslr,
  91};
  92
  93static const struct {
  94        char    alias[FTR_ALIAS_NAME_LEN];
  95        char    feature[FTR_ALIAS_OPTION_LEN];
  96} aliases[] __initconst = {
  97        { "kvm-arm.mode=nvhe",          "id_aa64mmfr1.vh=0" },
  98        { "kvm-arm.mode=protected",     "id_aa64mmfr1.vh=0" },
  99        { "arm64.nobti",                "id_aa64pfr1.bt=0" },
 100        { "arm64.nopauth",
 101          "id_aa64isar1.gpi=0 id_aa64isar1.gpa=0 "
 102          "id_aa64isar1.api=0 id_aa64isar1.apa=0"          },
 103        { "nokaslr",                    "kaslr.disabled=1" },
 104};
 105
 106static int __init find_field(const char *cmdline,
 107                             const struct ftr_set_desc *reg, int f, u64 *v)
 108{
 109        char opt[FTR_DESC_NAME_LEN + FTR_DESC_FIELD_LEN + 2];
 110        int len;
 111
 112        len = snprintf(opt, ARRAY_SIZE(opt), "%s.%s=",
 113                       reg->name, reg->fields[f].name);
 114
 115        if (!parameqn(cmdline, opt, len))
 116                return -1;
 117
 118        return kstrtou64(cmdline + len, 0, v);
 119}
 120
 121static void __init match_options(const char *cmdline)
 122{
 123        int i;
 124
 125        for (i = 0; i < ARRAY_SIZE(regs); i++) {
 126                int f;
 127
 128                if (!regs[i]->override)
 129                        continue;
 130
 131                for (f = 0; strlen(regs[i]->fields[f].name); f++) {
 132                        u64 shift = regs[i]->fields[f].shift;
 133                        u64 mask = 0xfUL << shift;
 134                        u64 v;
 135
 136                        if (find_field(cmdline, regs[i], f, &v))
 137                                continue;
 138
 139                        /*
 140                         * If an override gets filtered out, advertise
 141                         * it by setting the value to 0xf, but
 142                         * clearing the mask... Yes, this is fragile.
 143                         */
 144                        if (regs[i]->fields[f].filter &&
 145                            !regs[i]->fields[f].filter(v)) {
 146                                regs[i]->override->val  |= mask;
 147                                regs[i]->override->mask &= ~mask;
 148                                continue;
 149                        }
 150
 151                        regs[i]->override->val  &= ~mask;
 152                        regs[i]->override->val  |= (v << shift) & mask;
 153                        regs[i]->override->mask |= mask;
 154
 155                        return;
 156                }
 157        }
 158}
 159
 160static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
 161{
 162        do {
 163                char buf[256];
 164                size_t len;
 165                int i;
 166
 167                cmdline = skip_spaces(cmdline);
 168
 169                for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++);
 170                if (!len)
 171                        return;
 172
 173                len = min(len, ARRAY_SIZE(buf) - 1);
 174                strncpy(buf, cmdline, len);
 175                buf[len] = 0;
 176
 177                if (strcmp(buf, "--") == 0)
 178                        return;
 179
 180                cmdline += len;
 181
 182                match_options(buf);
 183
 184                for (i = 0; parse_aliases && i < ARRAY_SIZE(aliases); i++)
 185                        if (parameq(buf, aliases[i].alias))
 186                                __parse_cmdline(aliases[i].feature, false);
 187        } while (1);
 188}
 189
 190static __init const u8 *get_bootargs_cmdline(void)
 191{
 192        const u8 *prop;
 193        void *fdt;
 194        int node;
 195
 196        fdt = get_early_fdt_ptr();
 197        if (!fdt)
 198                return NULL;
 199
 200        node = fdt_path_offset(fdt, "/chosen");
 201        if (node < 0)
 202                return NULL;
 203
 204        prop = fdt_getprop(fdt, node, "bootargs", NULL);
 205        if (!prop)
 206                return NULL;
 207
 208        return strlen(prop) ? prop : NULL;
 209}
 210
 211static __init void parse_cmdline(void)
 212{
 213        const u8 *prop = get_bootargs_cmdline();
 214
 215        if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !prop)
 216                __parse_cmdline(CONFIG_CMDLINE, true);
 217
 218        if (!IS_ENABLED(CONFIG_CMDLINE_FORCE) && prop)
 219                __parse_cmdline(prop, true);
 220}
 221
 222/* Keep checkers quiet */
 223void init_feature_override(void);
 224
 225asmlinkage void __init init_feature_override(void)
 226{
 227        int i;
 228
 229        for (i = 0; i < ARRAY_SIZE(regs); i++) {
 230                if (regs[i]->override) {
 231                        regs[i]->override->val  = 0;
 232                        regs[i]->override->mask = 0;
 233                }
 234        }
 235
 236        parse_cmdline();
 237
 238        for (i = 0; i < ARRAY_SIZE(regs); i++) {
 239                if (regs[i]->override)
 240                        dcache_clean_inval_poc((unsigned long)regs[i]->override,
 241                                            (unsigned long)regs[i]->override +
 242                                            sizeof(*regs[i]->override));
 243        }
 244}
 245