arch/powerpc/mm/pkeys.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  * PowerPC Memory Protection Keys management
   4  *
   5  * Copyright 2017, Ram Pai, IBM Corporation.
   6  */
   7
   8 #include <asm/mman.h>
   9 #include <asm/setup.h>
  10 #include <linux/pkeys.h>
  11 #include <linux/of_device.h>
  12
  13 DEFINE_STATIC_KEY_TRUE(pkey_disabled);
  14 bool pkey_execute_disable_supported;
  15 int  pkeys_total;               /* Total pkeys as per device tree */
  16 bool pkeys_devtree_defined;     /* pkey property exported by device tree */
  17 u32  initial_allocation_mask;   /* Bits set for the initially allocated keys */
  18 u32  reserved_allocation_mask;  /* Bits set for reserved keys */
  19 u64  pkey_amr_mask;             /* Bits in AMR not to be touched */
  20 u64  pkey_iamr_mask;            /* Bits in AMR not to be touched */
  21 u64  pkey_uamor_mask;           /* Bits in UMOR not to be touched */
  22 int  execute_only_key = 2;
  23
  24 #define AMR_BITS_PER_PKEY 2
  25 #define AMR_RD_BIT 0x1UL
  26 #define AMR_WR_BIT 0x2UL
  27 #define IAMR_EX_BIT 0x1UL
  28 #define PKEY_REG_BITS (sizeof(u64)*8)
  29 #define pkeyshift(pkey) (PKEY_REG_BITS - ((pkey+1) * AMR_BITS_PER_PKEY))
  30
  31 static void scan_pkey_feature(void)
  32 {
  33         u32 vals[2];
  34         struct device_node *cpu;
  35
  36         cpu = of_find_node_by_type(NULL, "cpu");
  37         if (!cpu)
  38                 return;
  39
  40         if (of_property_read_u32_array(cpu,
  41                         "ibm,processor-storage-keys", vals, 2))
  42                 return;
  43
  44         /*
  45          * Since any pkey can be used for data or execute, we will just treat
  46          * all keys as equal and track them as one entity.
  47          */
  48         pkeys_total = vals[0];
  49         pkeys_devtree_defined = true;
  50 }
  51
  52 static inline bool pkey_mmu_enabled(void)
  53 {
  54         if (firmware_has_feature(FW_FEATURE_LPAR))
  55                 return pkeys_total;
  56         else
  57                 return cpu_has_feature(CPU_FTR_PKEY);
  58 }
  59
  60 int pkey_initialize(void)
  61 {
  62         int os_reserved, i;
  63
  64         /*
  65          * We define PKEY_DISABLE_EXECUTE in addition to the arch-neutral
  66          * generic defines for PKEY_DISABLE_ACCESS and PKEY_DISABLE_WRITE.
  67          * Ensure that the bits a distinct.
  68          */
  69         BUILD_BUG_ON(PKEY_DISABLE_EXECUTE &
  70                      (PKEY_DISABLE_ACCESS | PKEY_DISABLE_WRITE));
  71
  72         /*
  73          * pkey_to_vmflag_bits() assumes that the pkey bits are contiguous
  74          * in the vmaflag. Make sure that is really the case.
  75          */
  76         BUILD_BUG_ON(__builtin_clzl(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT) +
  77                      __builtin_popcountl(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT)
  78                                 != (sizeof(u64) * BITS_PER_BYTE));
  79
  80         /* scan the device tree for pkey feature */
  81         scan_pkey_feature();
  82
  83         /*
  84          * Let's assume 32 pkeys on P8 bare metal, if its not defined by device
  85          * tree. We make this exception since skiboot forgot to expose this
  86          * property on power8.
  87          */
  88         if (!pkeys_devtree_defined && !firmware_has_feature(FW_FEATURE_LPAR) &&
  89                         cpu_has_feature(CPU_FTRS_POWER8))
  90                 pkeys_total = 32;
  91
  92         /*
  93          * Adjust the upper limit, based on the number of bits supported by
  94          * arch-neutral code.
  95          */
  96         pkeys_total = min_t(int, pkeys_total,
  97                         ((ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT)+1));
  98
  99         if (!pkey_mmu_enabled() || radix_enabled() || !pkeys_total)
 100                 static_branch_enable(&pkey_disabled);
 101         else
 102                 static_branch_disable(&pkey_disabled);
 103
 104         if (static_branch_likely(&pkey_disabled))
 105                 return 0;
 106
 107         /*
 108          * The device tree cannot be relied to indicate support for
 109          * execute_disable support. Instead we use a PVR check.
 110          */
 111         if (pvr_version_is(PVR_POWER7) || pvr_version_is(PVR_POWER7p))
 112                 pkey_execute_disable_supported = false;
 113         else
 114                 pkey_execute_disable_supported = true;
 115
 116 #ifdef CONFIG_PPC_4K_PAGES
 117         /*
 118          * The OS can manage only 8 pkeys due to its inability to represent them
 119          * in the Linux 4K PTE.
 120          */
 121         os_reserved = pkeys_total - 8;
 122 #else
 123         os_reserved = 0;
 124 #endif
 125         /* Bits are in LE format. */
 126         reserved_allocation_mask = (0x1 << 1) | (0x1 << execute_only_key);
 127
 128         /* register mask is in BE format */
 129         pkey_amr_mask = ~0x0ul;
 130         pkey_amr_mask &= ~(0x3ul << pkeyshift(0));
 131
 132         pkey_iamr_mask = ~0x0ul;
 133         pkey_iamr_mask &= ~(0x3ul << pkeyshift(0));
 134         pkey_iamr_mask &= ~(0x3ul << pkeyshift(execute_only_key));
 135
 136         pkey_uamor_mask = ~0x0ul;
 137         pkey_uamor_mask &= ~(0x3ul << pkeyshift(0));
 138         pkey_uamor_mask &= ~(0x3ul << pkeyshift(execute_only_key));
 139
 140         /* mark the rest of the keys as reserved and hence unavailable */
 141         for (i = (pkeys_total - os_reserved); i < pkeys_total; i++) {
 142                 reserved_allocation_mask |= (0x1 << i);
 143                 pkey_uamor_mask &= ~(0x3ul << pkeyshift(i));
 144         }
 145         initial_allocation_mask = reserved_allocation_mask | (0x1 << 0);
 146
 147         if (unlikely((pkeys_total - os_reserved) <= execute_only_key)) {
 148                 /*
 149                  * Insufficient number of keys to support
 150                  * execute only key. Mark it unavailable.
 151                  * Any AMR, UAMOR, IAMR bit set for
 152                  * this key is irrelevant since this key
 153                  * can never be allocated.
 154                  */
 155                 execute_only_key = -1;
 156         }
 157
 158         return 0;
 159 }
 160
 161 arch_initcall(pkey_initialize);
 162
 163 void pkey_mm_init(struct mm_struct *mm)
 164 {
 165         if (static_branch_likely(&pkey_disabled))
 166                 return;
 167         mm_pkey_allocation_map(mm) = initial_allocation_mask;
 168         mm->context.execute_only_pkey = execute_only_key;
 169 }
 170
 171 static inline u64 read_amr(void)
 172 {
 173         return mfspr(SPRN_AMR);
 174 }
 175
 176 static inline void write_amr(u64 value)
 177 {
 178         mtspr(SPRN_AMR, value);
 179 }
 180
 181 static inline u64 read_iamr(void)
 182 {
 183         if (!likely(pkey_execute_disable_supported))
 184                 return 0x0UL;
 185
 186         return mfspr(SPRN_IAMR);
 187 }
 188
 189 static inline void write_iamr(u64 value)
 190 {
 191         if (!likely(pkey_execute_disable_supported))
 192                 return;
 193
 194         mtspr(SPRN_IAMR, value);
 195 }
 196
 197 static inline u64 read_uamor(void)
 198 {
 199         return mfspr(SPRN_UAMOR);
 200 }
 201
 202 static inline void write_uamor(u64 value)
 203 {
 204         mtspr(SPRN_UAMOR, value);
 205 }
 206
 207 static bool is_pkey_enabled(int pkey)
 208 {
 209         u64 uamor = read_uamor();
 210         u64 pkey_bits = 0x3ul << pkeyshift(pkey);
 211         u64 uamor_pkey_bits = (uamor & pkey_bits);
 212
 213         /*
 214          * Both the bits in UAMOR corresponding to the key should be set or
 215          * reset.
 216          */
 217         WARN_ON(uamor_pkey_bits && (uamor_pkey_bits != pkey_bits));
 218         return !!(uamor_pkey_bits);
 219 }
 220
 221 static inline void init_amr(int pkey, u8 init_bits)
 222 {
 223         u64 new_amr_bits = (((u64)init_bits & 0x3UL) << pkeyshift(pkey));
 224         u64 old_amr = read_amr() & ~((u64)(0x3ul) << pkeyshift(pkey));
 225
 226         write_amr(old_amr | new_amr_bits);
 227 }
 228
 229 static inline void init_iamr(int pkey, u8 init_bits)
 230 {
 231         u64 new_iamr_bits = (((u64)init_bits & 0x1UL) << pkeyshift(pkey));
 232         u64 old_iamr = read_iamr() & ~((u64)(0x1ul) << pkeyshift(pkey));
 233
 234         write_iamr(old_iamr | new_iamr_bits);
 235 }
 236
 237 /*
 238  * Set the access rights in AMR IAMR and UAMOR registers for @pkey to that
 239  * specified in @init_val.
 240  */
 241 int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 242                                 unsigned long init_val)
 243 {
 244         u64 new_amr_bits = 0x0ul;
 245         u64 new_iamr_bits = 0x0ul;
 246
 247         if (!is_pkey_enabled(pkey))
 248                 return -EINVAL;
 249
 250         if (init_val & PKEY_DISABLE_EXECUTE) {
 251                 if (!pkey_execute_disable_supported)
 252                         return -EINVAL;
 253                 new_iamr_bits |= IAMR_EX_BIT;
 254         }
 255         init_iamr(pkey, new_iamr_bits);
 256
 257         /* Set the bits we need in AMR: */
 258         if (init_val & PKEY_DISABLE_ACCESS)
 259                 new_amr_bits |= AMR_RD_BIT | AMR_WR_BIT;
 260         else if (init_val & PKEY_DISABLE_WRITE)
 261                 new_amr_bits |= AMR_WR_BIT;
 262
 263         init_amr(pkey, new_amr_bits);
 264         return 0;
 265 }
 266
 267 void thread_pkey_regs_save(struct thread_struct *thread)
 268 {
 269         if (static_branch_likely(&pkey_disabled))
 270                 return;
 271
 272         /*
 273          * TODO: Skip saving registers if @thread hasn't used any keys yet.
 274          */
 275         thread->amr = read_amr();
 276         thread->iamr = read_iamr();
 277         thread->uamor = read_uamor();
 278 }
 279
 280 void thread_pkey_regs_restore(struct thread_struct *new_thread,
 281                               struct thread_struct *old_thread)
 282 {
 283         if (static_branch_likely(&pkey_disabled))
 284                 return;
 285
 286         if (old_thread->amr != new_thread->amr)
 287                 write_amr(new_thread->amr);
 288         if (old_thread->iamr != new_thread->iamr)
 289                 write_iamr(new_thread->iamr);
 290         if (old_thread->uamor != new_thread->uamor)
 291                 write_uamor(new_thread->uamor);
 292 }
 293
 294 void thread_pkey_regs_init(struct thread_struct *thread)
 295 {
 296         if (static_branch_likely(&pkey_disabled))
 297                 return;
 298
 299         thread->amr = pkey_amr_mask;
 300         thread->iamr = pkey_iamr_mask;
 301         thread->uamor = pkey_uamor_mask;
 302
 303         write_uamor(pkey_uamor_mask);
 304         write_amr(pkey_amr_mask);
 305         write_iamr(pkey_iamr_mask);
 306 }
 307
 308 static inline bool pkey_allows_readwrite(int pkey)
 309 {
 310         int pkey_shift = pkeyshift(pkey);
 311
 312         if (!is_pkey_enabled(pkey))
 313                 return true;
 314
 315         return !(read_amr() & ((AMR_RD_BIT|AMR_WR_BIT) << pkey_shift));
 316 }
 317
 318 int __execute_only_pkey(struct mm_struct *mm)
 319 {
 320         return mm->context.execute_only_pkey;
 321 }
 322
 323 static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
 324 {
 325         /* Do this check first since the vm_flags should be hot */
 326         if ((vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) != VM_EXEC)
 327                 return false;
 328
 329         return (vma_pkey(vma) == vma->vm_mm->context.execute_only_pkey);
 330 }
 331
 332 /*
 333  * This should only be called for *plain* mprotect calls.
 334  */
 335 int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
 336                                   int pkey)
 337 {
 338         /*
 339          * If the currently associated pkey is execute-only, but the requested
 340          * protection is not execute-only, move it back to the default pkey.
 341          */
 342         if (vma_is_pkey_exec_only(vma) && (prot != PROT_EXEC))
 343                 return 0;
 344
 345         /*
 346          * The requested protection is execute-only. Hence let's use an
 347          * execute-only pkey.
 348          */
 349         if (prot == PROT_EXEC) {
 350                 pkey = execute_only_pkey(vma->vm_mm);
 351                 if (pkey > 0)
 352                         return pkey;
 353         }
 354
 355         /* Nothing to override. */
 356         return vma_pkey(vma);
 357 }
 358
 359 static bool pkey_access_permitted(int pkey, bool write, bool execute)
 360 {
 361         int pkey_shift;
 362         u64 amr;
 363
 364         if (!is_pkey_enabled(pkey))
 365                 return true;
 366
 367         pkey_shift = pkeyshift(pkey);
 368         if (execute && !(read_iamr() & (IAMR_EX_BIT << pkey_shift)))
 369                 return true;
 370
 371         amr = read_amr(); /* Delay reading amr until absolutely needed */
 372         return ((!write && !(amr & (AMR_RD_BIT << pkey_shift))) ||
 373                 (write &&  !(amr & (AMR_WR_BIT << pkey_shift))));
 374 }
 375
 376 bool arch_pte_access_permitted(u64 pte, bool write, bool execute)
 377 {
 378         if (static_branch_likely(&pkey_disabled))
 379                 return true;
 380
 381         return pkey_access_permitted(pte_to_pkey_bits(pte), write, execute);
 382 }
 383
 384 /*
 385  * We only want to enforce protection keys on the current thread because we
 386  * effectively have no access to AMR/IAMR for other threads or any way to tell
 387  * which AMR/IAMR in a threaded process we could use.
 388  *
 389  * So do not enforce things if the VMA is not from the current mm, or if we are
 390  * in a kernel thread.
 391  */
 392 static inline bool vma_is_foreign(struct vm_area_struct *vma)
 393 {
 394         if (!current->mm)
 395                 return true;
 396
 397         /* if it is not our ->mm, it has to be foreign */
 398         if (current->mm != vma->vm_mm)
 399                 return true;
 400
 401         return false;
 402 }
 403
 404 bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write,
 405                                bool execute, bool foreign)
 406 {
 407         if (static_branch_likely(&pkey_disabled))
 408                 return true;
 409         /*
 410          * Do not enforce our key-permissions on a foreign vma.
 411          */
 412         if (foreign || vma_is_foreign(vma))
 413                 return true;
 414
 415         return pkey_access_permitted(vma_pkey(vma), write, execute);
 416 }