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                 {}
  58         },
  59 };
  60
  61 static 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
  73 extern struct arm64_ftr_override kaslr_feature_override;
  74
  75 static 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
  86 static const struct ftr_set_desc * const regs[] __initconst = {
  87         &mmfr1,
  88         &pfr1,
  89         &isar1,
  90         &kaslr,
  91 };
  92
  93 static 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
 106 static 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
 121 static 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
 160 static __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
 190 static __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
 211 static __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 */
 223 void init_feature_override(void);
 224
 225 asmlinkage 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 }