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/mmu_context.h>
  10 #include <asm/setup.h>
  11 #include <linux/pkeys.h>
  12 #include <linux/of_device.h>
  13
  14 DEFINE_STATIC_KEY_TRUE(pkey_disabled);
  15 int  pkeys_total;               /* Total pkeys as per device tree */
  16 u32  initial_allocation_mask;   /* Bits set for the initially allocated keys */
  17 u32  reserved_allocation_mask;  /* Bits set for reserved keys */
  18 static bool pkey_execute_disable_supported;
  19 static bool pkeys_devtree_defined;      /* property exported by device tree */
  20 static u64 pkey_amr_mask;               /* Bits in AMR not to be touched */
  21 static u64 pkey_iamr_mask;              /* Bits in AMR not to be touched */
  22 static u64 pkey_uamor_mask;             /* Bits in UMOR not to be touched */
  23 static int execute_only_key = 2;
  24
  25 #define AMR_BITS_PER_PKEY 2
  26 #define AMR_RD_BIT 0x1UL
  27 #define AMR_WR_BIT 0x2UL
  28 #define IAMR_EX_BIT 0x1UL
  29 #define PKEY_REG_BITS (sizeof(u64)*8)
  30 #define pkeyshift(pkey) (PKEY_REG_BITS - ((pkey+1) * AMR_BITS_PER_PKEY))
  31
  32 static void scan_pkey_feature(void)
  33 {
  34         u32 vals[2];
  35         struct device_node *cpu;
  36
  37         cpu = of_find_node_by_type(NULL, "cpu");
  38         if (!cpu)
  39                 return;
  40
  41         if (of_property_read_u32_array(cpu,
  42                         "ibm,processor-storage-keys", vals, 2))
  43                 return;
  44
  45         /*
  46          * Since any pkey can be used for data or execute, we will just treat
  47          * all keys as equal and track them as one entity.
  48          */
  49         pkeys_total = vals[0];
  50         pkeys_devtree_defined = true;
  51 }
  52
  53 static inline bool pkey_mmu_enabled(void)
  54 {
  55         if (firmware_has_feature(FW_FEATURE_LPAR))
  56                 return pkeys_total;
  57         else
  58                 return cpu_has_feature(CPU_FTR_PKEY);
  59 }
  60
  61 static int pkey_initialize(void)
  62 {
  63         int os_reserved, i;
  64
  65         /*
  66          * We define PKEY_DISABLE_EXECUTE in addition to the arch-neutral
  67          * generic defines for PKEY_DISABLE_ACCESS and PKEY_DISABLE_WRITE.
  68          * Ensure that the bits a distinct.
  69          */
  70         BUILD_BUG_ON(PKEY_DISABLE_EXECUTE &
  71                      (PKEY_DISABLE_ACCESS | PKEY_DISABLE_WRITE));
  72
  73         /*
  74          * pkey_to_vmflag_bits() assumes that the pkey bits are contiguous
  75          * in the vmaflag. Make sure that is really the case.
  76          */
  77         BUILD_BUG_ON(__builtin_clzl(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT) +
  78                      __builtin_popcountl(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT)
  79                                 != (sizeof(u64) * BITS_PER_BYTE));
  80
  81         /* scan the device tree for pkey feature */
  82         scan_pkey_feature();
  83
  84         /*
  85          * Let's assume 32 pkeys on P8 bare metal, if its not defined by device
  86          * tree. We make this exception since skiboot forgot to expose this
  87          * property on power8.
  88          */
  89         if (!pkeys_devtree_defined && !firmware_has_feature(FW_FEATURE_LPAR) &&
  90                         cpu_has_feature(CPU_FTRS_POWER8))
  91                 pkeys_total = 32;
  92
  93         /*
  94          * Adjust the upper limit, based on the number of bits supported by
  95          * arch-neutral code.
  96          */
  97         pkeys_total = min_t(int, pkeys_total,
  98                         ((ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT)+1));
  99
 100         if (!pkey_mmu_enabled() || radix_enabled() || !pkeys_total)
 101                 static_branch_enable(&pkey_disabled);
 102         else
 103                 static_branch_disable(&pkey_disabled);
 104
 105         if (static_branch_likely(&pkey_disabled))
 106                 return 0;
 107
 108         /*
 109          * The device tree cannot be relied to indicate support for
 110          * execute_disable support. Instead we use a PVR check.
 111          */
 112         if (pvr_version_is(PVR_POWER7) || pvr_version_is(PVR_POWER7p))
 113                 pkey_execute_disable_supported = false;
 114         else
 115                 pkey_execute_disable_supported = true;
 116
 117 #ifdef CONFIG_PPC_4K_PAGES
 118         /*
 119          * The OS can manage only 8 pkeys due to its inability to represent them
 120          * in the Linux 4K PTE.
 121          */
 122         os_reserved = pkeys_total - 8;
 123 #else
 124         os_reserved = 0;
 125 #endif
 126         /* Bits are in LE format. */
 127         reserved_allocation_mask = (0x1 << 1) | (0x1 << execute_only_key);
 128
 129         /* register mask is in BE format */
 130         pkey_amr_mask = ~0x0ul;
 131         pkey_amr_mask &= ~(0x3ul << pkeyshift(0));
 132
 133         pkey_iamr_mask = ~0x0ul;
 134         pkey_iamr_mask &= ~(0x3ul << pkeyshift(0));
 135         pkey_iamr_mask &= ~(0x3ul << pkeyshift(execute_only_key));
 136
 137         pkey_uamor_mask = ~0x0ul;
 138         pkey_uamor_mask &= ~(0x3ul << pkeyshift(0));
 139         pkey_uamor_mask &= ~(0x3ul << pkeyshift(execute_only_key));
 140
 141         /* mark the rest of the keys as reserved and hence unavailable */
 142         for (i = (pkeys_total - os_reserved); i < pkeys_total; i++) {
 143                 reserved_allocation_mask |= (0x1 << i);
 144                 pkey_uamor_mask &= ~(0x3ul << pkeyshift(i));
 145         }
 146         initial_allocation_mask = reserved_allocation_mask | (0x1 << 0);
 147
 148         if (unlikely((pkeys_total - os_reserved) <= execute_only_key)) {
 149                 /*
 150                  * Insufficient number of keys to support
 151                  * execute only key. Mark it unavailable.
 152                  * Any AMR, UAMOR, IAMR bit set for
 153                  * this key is irrelevant since this key
 154                  * can never be allocated.
 155                  */
 156                 execute_only_key = -1;
 157         }
 158
 159         return 0;
 160 }
 161
 162 arch_initcall(pkey_initialize);
 163
 164 void pkey_mm_init(struct mm_struct *mm)
 165 {
 166         if (static_branch_likely(&pkey_disabled))
 167                 return;
 168         mm_pkey_allocation_map(mm) = initial_allocation_mask;
 169         mm->context.execute_only_pkey = execute_only_key;
 170 }
 171
 172 static inline u64 read_amr(void)
 173 {
 174         return mfspr(SPRN_AMR);
 175 }
 176
 177 static inline void write_amr(u64 value)
 178 {
 179         mtspr(SPRN_AMR, value);
 180 }
 181
 182 static inline u64 read_iamr(void)
 183 {
 184         if (!likely(pkey_execute_disable_supported))
 185                 return 0x0UL;
 186
 187         return mfspr(SPRN_IAMR);
 188 }
 189
 190 static inline void write_iamr(u64 value)
 191 {
 192         if (!likely(pkey_execute_disable_supported))
 193                 return;
 194
 195         mtspr(SPRN_IAMR, value);
 196 }
 197
 198 static inline u64 read_uamor(void)
 199 {
 200         return mfspr(SPRN_UAMOR);
 201 }
 202
 203 static inline void write_uamor(u64 value)
 204 {
 205         mtspr(SPRN_UAMOR, value);
 206 }
 207
 208 static bool is_pkey_enabled(int pkey)
 209 {
 210         u64 uamor = read_uamor();
 211         u64 pkey_bits = 0x3ul << pkeyshift(pkey);
 212         u64 uamor_pkey_bits = (uamor & pkey_bits);
 213
 214         /*
 215          * Both the bits in UAMOR corresponding to the key should be set or
 216          * reset.
 217          */
 218         WARN_ON(uamor_pkey_bits && (uamor_pkey_bits != pkey_bits));
 219         return !!(uamor_pkey_bits);
 220 }
 221
 222 static inline void init_amr(int pkey, u8 init_bits)
 223 {
 224         u64 new_amr_bits = (((u64)init_bits & 0x3UL) << pkeyshift(pkey));
 225         u64 old_amr = read_amr() & ~((u64)(0x3ul) << pkeyshift(pkey));
 226
 227         write_amr(old_amr | new_amr_bits);
 228 }
 229
 230 static inline void init_iamr(int pkey, u8 init_bits)
 231 {
 232         u64 new_iamr_bits = (((u64)init_bits & 0x1UL) << pkeyshift(pkey));
 233         u64 old_iamr = read_iamr() & ~((u64)(0x1ul) << pkeyshift(pkey));
 234
 235         write_iamr(old_iamr | new_iamr_bits);
 236 }
 237
 238 /*
 239  * Set the access rights in AMR IAMR and UAMOR registers for @pkey to that
 240  * specified in @init_val.
 241  */
 242 int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 243                                 unsigned long init_val)
 244 {
 245         u64 new_amr_bits = 0x0ul;
 246         u64 new_iamr_bits = 0x0ul;
 247
 248         if (!is_pkey_enabled(pkey))
 249                 return -EINVAL;
 250
 251         if (init_val & PKEY_DISABLE_EXECUTE) {
 252                 if (!pkey_execute_disable_supported)
 253                         return -EINVAL;
 254                 new_iamr_bits |= IAMR_EX_BIT;
 255         }
 256         init_iamr(pkey, new_iamr_bits);
 257
 258         /* Set the bits we need in AMR: */
 259         if (init_val & PKEY_DISABLE_ACCESS)
 260                 new_amr_bits |= AMR_RD_BIT | AMR_WR_BIT;
 261         else if (init_val & PKEY_DISABLE_WRITE)
 262                 new_amr_bits |= AMR_WR_BIT;
 263
 264         init_amr(pkey, new_amr_bits);
 265         return 0;
 266 }
 267
 268 void thread_pkey_regs_save(struct thread_struct *thread)
 269 {
 270         if (static_branch_likely(&pkey_disabled))
 271                 return;
 272
 273         /*
 274          * TODO: Skip saving registers if @thread hasn't used any keys yet.
 275          */
 276         thread->amr = read_amr();
 277         thread->iamr = read_iamr();
 278         thread->uamor = read_uamor();
 279 }
 280
 281 void thread_pkey_regs_restore(struct thread_struct *new_thread,
 282                               struct thread_struct *old_thread)
 283 {
 284         if (static_branch_likely(&pkey_disabled))
 285                 return;
 286
 287         if (old_thread->amr != new_thread->amr)
 288                 write_amr(new_thread->amr);
 289         if (old_thread->iamr != new_thread->iamr)
 290                 write_iamr(new_thread->iamr);
 291         if (old_thread->uamor != new_thread->uamor)
 292                 write_uamor(new_thread->uamor);
 293 }
 294
 295 void thread_pkey_regs_init(struct thread_struct *thread)
 296 {
 297         if (static_branch_likely(&pkey_disabled))
 298                 return;
 299
 300         thread->amr = pkey_amr_mask;
 301         thread->iamr = pkey_iamr_mask;
 302         thread->uamor = pkey_uamor_mask;
 303
 304         write_uamor(pkey_uamor_mask);
 305         write_amr(pkey_amr_mask);
 306         write_iamr(pkey_iamr_mask);
 307 }
 308
 309 static inline bool pkey_allows_readwrite(int pkey)
 310 {
 311         int pkey_shift = pkeyshift(pkey);
 312
 313         if (!is_pkey_enabled(pkey))
 314                 return true;
 315
 316         return !(read_amr() & ((AMR_RD_BIT|AMR_WR_BIT) << pkey_shift));
 317 }
 318
 319 int __execute_only_pkey(struct mm_struct *mm)
 320 {
 321         return mm->context.execute_only_pkey;
 322 }
 323
 324 static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
 325 {
 326         /* Do this check first since the vm_flags should be hot */
 327         if ((vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) != VM_EXEC)
 328                 return false;
 329
 330         return (vma_pkey(vma) == vma->vm_mm->context.execute_only_pkey);
 331 }
 332
 333 /*
 334  * This should only be called for *plain* mprotect calls.
 335  */
 336 int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
 337                                   int pkey)
 338 {
 339         /*
 340          * If the currently associated pkey is execute-only, but the requested
 341          * protection is not execute-only, move it back to the default pkey.
 342          */
 343         if (vma_is_pkey_exec_only(vma) && (prot != PROT_EXEC))
 344                 return 0;
 345
 346         /*
 347          * The requested protection is execute-only. Hence let's use an
 348          * execute-only pkey.
 349          */
 350         if (prot == PROT_EXEC) {
 351                 pkey = execute_only_pkey(vma->vm_mm);
 352                 if (pkey > 0)
 353                         return pkey;
 354         }
 355
 356         /* Nothing to override. */
 357         return vma_pkey(vma);
 358 }
 359
 360 static bool pkey_access_permitted(int pkey, bool write, bool execute)
 361 {
 362         int pkey_shift;
 363         u64 amr;
 364
 365         if (!is_pkey_enabled(pkey))
 366                 return true;
 367
 368         pkey_shift = pkeyshift(pkey);
 369         if (execute && !(read_iamr() & (IAMR_EX_BIT << pkey_shift)))
 370                 return true;
 371
 372         amr = read_amr(); /* Delay reading amr until absolutely needed */
 373         return ((!write && !(amr & (AMR_RD_BIT << pkey_shift))) ||
 374                 (write &&  !(amr & (AMR_WR_BIT << pkey_shift))));
 375 }
 376
 377 bool arch_pte_access_permitted(u64 pte, bool write, bool execute)
 378 {
 379         if (static_branch_likely(&pkey_disabled))
 380                 return true;
 381
 382         return pkey_access_permitted(pte_to_pkey_bits(pte), write, execute);
 383 }
 384
 385 /*
 386  * We only want to enforce protection keys on the current thread because we
 387  * effectively have no access to AMR/IAMR for other threads or any way to tell
 388  * which AMR/IAMR in a threaded process we could use.
 389  *
 390  * So do not enforce things if the VMA is not from the current mm, or if we are
 391  * in a kernel thread.
 392  */
 393 static inline bool vma_is_foreign(struct vm_area_struct *vma)
 394 {
 395         if (!current->mm)
 396                 return true;
 397
 398         /* if it is not our ->mm, it has to be foreign */
 399         if (current->mm != vma->vm_mm)
 400                 return true;
 401
 402         return false;
 403 }
 404
 405 bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write,
 406                                bool execute, bool foreign)
 407 {
 408         if (static_branch_likely(&pkey_disabled))
 409                 return true;
 410         /*
 411          * Do not enforce our key-permissions on a foreign vma.
 412          */
 413         if (foreign || vma_is_foreign(vma))
 414                 return true;
 415
 416         return pkey_access_permitted(vma_pkey(vma), write, execute);
 417 }
 418
 419 void arch_dup_pkeys(struct mm_struct *oldmm, struct mm_struct *mm)
 420 {
 421         if (static_branch_likely(&pkey_disabled))
 422                 return;
 423
 424         /* Duplicate the oldmm pkey state in mm: */
 425         mm_pkey_allocation_map(mm) = mm_pkey_allocation_map(oldmm);
 426         mm->context.execute_only_pkey = oldmm->context.execute_only_pkey;
 427 }