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