arch/arm64/kernel/idreg-override.c

   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    116
  21
  22 struct 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
  32 static 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
  43 static 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
  52 static 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                 { "mte", ID_AA64PFR1_MTE_SHIFT},
  58                 {}
  59         },
  60 };
  61
  62 static const struct ftr_set_desc isar1 __initconst = {
  63         .name           = "id_aa64isar1",
  64         .override       = &id_aa64isar1_override,
  65         .fields         = {
  66                 { "gpi", ID_AA64ISAR1_GPI_SHIFT },
  67                 { "gpa", ID_AA64ISAR1_GPA_SHIFT },
  68                 { "api", ID_AA64ISAR1_API_SHIFT },
  69                 { "apa", ID_AA64ISAR1_APA_SHIFT },
  70                 {}
  71         },
  72 };
  73
  74 static const struct ftr_set_desc isar2 __initconst = {
  75         .name           = "id_aa64isar2",
  76         .override       = &id_aa64isar2_override,
  77         .fields         = {
  78                 { "gpa3", ID_AA64ISAR2_GPA3_SHIFT },
  79                 { "apa3", ID_AA64ISAR2_APA3_SHIFT },
  80                 {}
  81         },
  82 };
  83
  84 extern struct arm64_ftr_override kaslr_feature_override;
  85
  86 static const struct ftr_set_desc kaslr __initconst = {
  87         .name           = "kaslr",
  88 #ifdef CONFIG_RANDOMIZE_BASE
  89         .override       = &kaslr_feature_override,
  90 #endif
  91         .fields         = {
  92                 { "disabled", 0 },
  93                 {}
  94         },
  95 };
  96
  97 static const struct ftr_set_desc * const regs[] __initconst = {
  98         &mmfr1,
  99         &pfr1,
 100         &isar1,
 101         &isar2,
 102         &kaslr,
 103 };
 104
 105 static const struct {
 106         char    alias[FTR_ALIAS_NAME_LEN];
 107         char    feature[FTR_ALIAS_OPTION_LEN];
 108 } aliases[] __initconst = {
 109         { "kvm-arm.mode=nvhe",          "id_aa64mmfr1.vh=0" },
 110         { "kvm-arm.mode=protected",     "id_aa64mmfr1.vh=0" },
 111         { "arm64.nobti",                "id_aa64pfr1.bt=0" },
 112         { "arm64.nopauth",
 113           "id_aa64isar1.gpi=0 id_aa64isar1.gpa=0 "
 114           "id_aa64isar1.api=0 id_aa64isar1.apa=0 "
 115           "id_aa64isar2.gpa3=0 id_aa64isar2.apa3=0"        },
 116         { "arm64.nomte",                "id_aa64pfr1.mte=0" },
 117         { "nokaslr",                    "kaslr.disabled=1" },
 118 };
 119
 120 static int __init find_field(const char *cmdline,
 121                              const struct ftr_set_desc *reg, int f, u64 *v)
 122 {
 123         char opt[FTR_DESC_NAME_LEN + FTR_DESC_FIELD_LEN + 2];
 124         int len;
 125
 126         len = snprintf(opt, ARRAY_SIZE(opt), "%s.%s=",
 127                        reg->name, reg->fields[f].name);
 128
 129         if (!parameqn(cmdline, opt, len))
 130                 return -1;
 131
 132         return kstrtou64(cmdline + len, 0, v);
 133 }
 134
 135 static void __init match_options(const char *cmdline)
 136 {
 137         int i;
 138
 139         for (i = 0; i < ARRAY_SIZE(regs); i++) {
 140                 int f;
 141
 142                 if (!regs[i]->override)
 143                         continue;
 144
 145                 for (f = 0; strlen(regs[i]->fields[f].name); f++) {
 146                         u64 shift = regs[i]->fields[f].shift;
 147                         u64 mask = 0xfUL << shift;
 148                         u64 v;
 149
 150                         if (find_field(cmdline, regs[i], f, &v))
 151                                 continue;
 152
 153                         /*
 154                          * If an override gets filtered out, advertise
 155                          * it by setting the value to 0xf, but
 156                          * clearing the mask... Yes, this is fragile.
 157                          */
 158                         if (regs[i]->fields[f].filter &&
 159                             !regs[i]->fields[f].filter(v)) {
 160                                 regs[i]->override->val  |= mask;
 161                                 regs[i]->override->mask &= ~mask;
 162                                 continue;
 163                         }
 164
 165                         regs[i]->override->val  &= ~mask;
 166                         regs[i]->override->val  |= (v << shift) & mask;
 167                         regs[i]->override->mask |= mask;
 168
 169                         return;
 170                 }
 171         }
 172 }
 173
 174 static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
 175 {
 176         do {
 177                 char buf[256];
 178                 size_t len;
 179                 int i;
 180
 181                 cmdline = skip_spaces(cmdline);
 182
 183                 for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++);
 184                 if (!len)
 185                         return;
 186
 187                 len = min(len, ARRAY_SIZE(buf) - 1);
 188                 strncpy(buf, cmdline, len);
 189                 buf[len] = 0;
 190
 191                 if (strcmp(buf, "--") == 0)
 192                         return;
 193
 194                 cmdline += len;
 195
 196                 match_options(buf);
 197
 198                 for (i = 0; parse_aliases && i < ARRAY_SIZE(aliases); i++)
 199                         if (parameq(buf, aliases[i].alias))
 200                                 __parse_cmdline(aliases[i].feature, false);
 201         } while (1);
 202 }
 203
 204 static __init const u8 *get_bootargs_cmdline(void)
 205 {
 206         const u8 *prop;
 207         void *fdt;
 208         int node;
 209
 210         fdt = get_early_fdt_ptr();
 211         if (!fdt)
 212                 return NULL;
 213
 214         node = fdt_path_offset(fdt, "/chosen");
 215         if (node < 0)
 216                 return NULL;
 217
 218         prop = fdt_getprop(fdt, node, "bootargs", NULL);
 219         if (!prop)
 220                 return NULL;
 221
 222         return strlen(prop) ? prop : NULL;
 223 }
 224
 225 static __init void parse_cmdline(void)
 226 {
 227         const u8 *prop = get_bootargs_cmdline();
 228
 229         if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !prop)
 230                 __parse_cmdline(CONFIG_CMDLINE, true);
 231
 232         if (!IS_ENABLED(CONFIG_CMDLINE_FORCE) && prop)
 233                 __parse_cmdline(prop, true);
 234 }
 235
 236 /* Keep checkers quiet */
 237 void init_feature_override(void);
 238
 239 asmlinkage void __init init_feature_override(void)
 240 {
 241         int i;
 242
 243         for (i = 0; i < ARRAY_SIZE(regs); i++) {
 244                 if (regs[i]->override) {
 245                         regs[i]->override->val  = 0;
 246                         regs[i]->override->mask = 0;
 247                 }
 248         }
 249
 250         parse_cmdline();
 251
 252         for (i = 0; i < ARRAY_SIZE(regs); i++) {
 253                 if (regs[i]->override)
 254                         dcache_clean_inval_poc((unsigned long)regs[i]->override,
 255                                             (unsigned long)regs[i]->override +
 256                                             sizeof(*regs[i]->override));
 257         }
 258 }