arch/arm64/include/asm/uaccess.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * Based on arch/arm/include/asm/uaccess.h
   4  *
   5  * Copyright (C) 2012 ARM Ltd.
   6  */
   7 #ifndef __ASM_UACCESS_H
   8 #define __ASM_UACCESS_H
   9
  10 #include <asm/alternative.h>
  11 #include <asm/kernel-pgtable.h>
  12 #include <asm/sysreg.h>
  13
  14 /*
  15  * User space memory access functions
  16  */
  17 #include <linux/bitops.h>
  18 #include <linux/kasan-checks.h>
  19 #include <linux/string.h>
  20
  21 #include <asm/cpufeature.h>
  22 #include <asm/mmu.h>
  23 #include <asm/mte.h>
  24 #include <asm/ptrace.h>
  25 #include <asm/memory.h>
  26 #include <asm/extable.h>
  27
  28 #define HAVE_GET_KERNEL_NOFAULT
  29
  30 /*
  31  * Test whether a block of memory is a valid user space address.
  32  * Returns 1 if the range is valid, 0 otherwise.
  33  *
  34  * This is equivalent to the following test:
  35  * (u65)addr + (u65)size <= (u65)TASK_SIZE_MAX
  36  */
  37 static inline unsigned long __range_ok(const void __user *addr, unsigned long size)
  38 {
  39         unsigned long ret, limit = TASK_SIZE_MAX - 1;
  40
  41         /*
  42          * Asynchronous I/O running in a kernel thread does not have the
  43          * TIF_TAGGED_ADDR flag of the process owning the mm, so always untag
  44          * the user address before checking.
  45          */
  46         if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI) &&
  47             (current->flags & PF_KTHREAD || test_thread_flag(TIF_TAGGED_ADDR)))
  48                 addr = untagged_addr(addr);
  49
  50         __chk_user_ptr(addr);
  51         asm volatile(
  52         // A + B <= C + 1 for all A,B,C, in four easy steps:
  53         // 1: X = A + B; X' = X % 2^64
  54         "       adds    %0, %3, %2\n"
  55         // 2: Set C = 0 if X > 2^64, to guarantee X' > C in step 4
  56         "       csel    %1, xzr, %1, hi\n"
  57         // 3: Set X' = ~0 if X >= 2^64. For X == 2^64, this decrements X'
  58         //    to compensate for the carry flag being set in step 4. For
  59         //    X > 2^64, X' merely has to remain nonzero, which it does.
  60         "       csinv   %0, %0, xzr, cc\n"
  61         // 4: For X < 2^64, this gives us X' - C - 1 <= 0, where the -1
  62         //    comes from the carry in being clear. Otherwise, we are
  63         //    testing X' - C == 0, subject to the previous adjustments.
  64         "       sbcs    xzr, %0, %1\n"
  65         "       cset    %0, ls\n"
  66         : "=&r" (ret), "+r" (limit) : "Ir" (size), "0" (addr) : "cc");
  67
  68         return ret;
  69 }
  70
  71 #define access_ok(addr, size)   __range_ok(addr, size)
  72
  73 #define _ASM_EXTABLE(from, to)                                          \
  74         "       .pushsection    __ex_table, \"a\"\n"                    \
  75         "       .align          3\n"                                    \
  76         "       .long           (" #from " - .), (" #to " - .)\n"       \
  77         "       .popsection\n"
  78
  79 /*
  80  * User access enabling/disabling.
  81  */
  82 #ifdef CONFIG_ARM64_SW_TTBR0_PAN
  83 static inline void __uaccess_ttbr0_disable(void)
  84 {
  85         unsigned long flags, ttbr;
  86
  87         local_irq_save(flags);
  88         ttbr = read_sysreg(ttbr1_el1);
  89         ttbr &= ~TTBR_ASID_MASK;
  90         /* reserved_pg_dir placed before swapper_pg_dir */
  91         write_sysreg(ttbr - RESERVED_SWAPPER_OFFSET, ttbr0_el1);
  92         isb();
  93         /* Set reserved ASID */
  94         write_sysreg(ttbr, ttbr1_el1);
  95         isb();
  96         local_irq_restore(flags);
  97 }
  98
  99 static inline void __uaccess_ttbr0_enable(void)
 100 {
 101         unsigned long flags, ttbr0, ttbr1;
 102
 103         /*
 104          * Disable interrupts to avoid preemption between reading the 'ttbr0'
 105          * variable and the MSR. A context switch could trigger an ASID
 106          * roll-over and an update of 'ttbr0'.
 107          */
 108         local_irq_save(flags);
 109         ttbr0 = READ_ONCE(current_thread_info()->ttbr0);
 110
 111         /* Restore active ASID */
 112         ttbr1 = read_sysreg(ttbr1_el1);
 113         ttbr1 &= ~TTBR_ASID_MASK;               /* safety measure */
 114         ttbr1 |= ttbr0 & TTBR_ASID_MASK;
 115         write_sysreg(ttbr1, ttbr1_el1);
 116         isb();
 117
 118         /* Restore user page table */
 119         write_sysreg(ttbr0, ttbr0_el1);
 120         isb();
 121         local_irq_restore(flags);
 122 }
 123
 124 static inline bool uaccess_ttbr0_disable(void)
 125 {
 126         if (!system_uses_ttbr0_pan())
 127                 return false;
 128         __uaccess_ttbr0_disable();
 129         return true;
 130 }
 131
 132 static inline bool uaccess_ttbr0_enable(void)
 133 {
 134         if (!system_uses_ttbr0_pan())
 135                 return false;
 136         __uaccess_ttbr0_enable();
 137         return true;
 138 }
 139 #else
 140 static inline bool uaccess_ttbr0_disable(void)
 141 {
 142         return false;
 143 }
 144
 145 static inline bool uaccess_ttbr0_enable(void)
 146 {
 147         return false;
 148 }
 149 #endif
 150
 151 static inline void __uaccess_disable_hw_pan(void)
 152 {
 153         asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_HAS_PAN,
 154                         CONFIG_ARM64_PAN));
 155 }
 156
 157 static inline void __uaccess_enable_hw_pan(void)
 158 {
 159         asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN,
 160                         CONFIG_ARM64_PAN));
 161 }
 162
 163 /*
 164  * The Tag Check Flag (TCF) mode for MTE is per EL, hence TCF0
 165  * affects EL0 and TCF affects EL1 irrespective of which TTBR is
 166  * used.
 167  * The kernel accesses TTBR0 usually with LDTR/STTR instructions
 168  * when UAO is available, so these would act as EL0 accesses using
 169  * TCF0.
 170  * However futex.h code uses exclusives which would be executed as
 171  * EL1, this can potentially cause a tag check fault even if the
 172  * user disables TCF0.
 173  *
 174  * To address the problem we set the PSTATE.TCO bit in uaccess_enable()
 175  * and reset it in uaccess_disable().
 176  *
 177  * The Tag check override (TCO) bit disables temporarily the tag checking
 178  * preventing the issue.
 179  */
 180 static inline void __uaccess_disable_tco(void)
 181 {
 182         asm volatile(ALTERNATIVE("nop", SET_PSTATE_TCO(0),
 183                                  ARM64_MTE, CONFIG_KASAN_HW_TAGS));
 184 }
 185
 186 static inline void __uaccess_enable_tco(void)
 187 {
 188         asm volatile(ALTERNATIVE("nop", SET_PSTATE_TCO(1),
 189                                  ARM64_MTE, CONFIG_KASAN_HW_TAGS));
 190 }
 191
 192 /*
 193  * These functions disable tag checking only if in MTE async mode
 194  * since the sync mode generates exceptions synchronously and the
 195  * nofault or load_unaligned_zeropad can handle them.
 196  */
 197 static inline void __uaccess_disable_tco_async(void)
 198 {
 199         if (system_uses_mte_async_mode())
 200                  __uaccess_disable_tco();
 201 }
 202
 203 static inline void __uaccess_enable_tco_async(void)
 204 {
 205         if (system_uses_mte_async_mode())
 206                 __uaccess_enable_tco();
 207 }
 208
 209 static inline void uaccess_disable_privileged(void)
 210 {
 211         __uaccess_disable_tco();
 212
 213         if (uaccess_ttbr0_disable())
 214                 return;
 215
 216         __uaccess_enable_hw_pan();
 217 }
 218
 219 static inline void uaccess_enable_privileged(void)
 220 {
 221         __uaccess_enable_tco();
 222
 223         if (uaccess_ttbr0_enable())
 224                 return;
 225
 226         __uaccess_disable_hw_pan();
 227 }
 228
 229 /*
 230  * Sanitise a uaccess pointer such that it becomes NULL if above the maximum
 231  * user address. In case the pointer is tagged (has the top byte set), untag
 232  * the pointer before checking.
 233  */
 234 #define uaccess_mask_ptr(ptr) (__typeof__(ptr))__uaccess_mask_ptr(ptr)
 235 static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
 236 {
 237         void __user *safe_ptr;
 238
 239         asm volatile(
 240         "       bics    xzr, %3, %2\n"
 241         "       csel    %0, %1, xzr, eq\n"
 242         : "=&r" (safe_ptr)
 243         : "r" (ptr), "r" (TASK_SIZE_MAX - 1),
 244           "r" (untagged_addr(ptr))
 245         : "cc");
 246
 247         csdb();
 248         return safe_ptr;
 249 }
 250
 251 /*
 252  * The "__xxx" versions of the user access functions do not verify the address
 253  * space - it must have been done previously with a separate "access_ok()"
 254  * call.
 255  *
 256  * The "__xxx_error" versions set the third argument to -EFAULT if an error
 257  * occurs, and leave it unchanged on success.
 258  */
 259 #define __get_mem_asm(load, reg, x, addr, err)                          \
 260         asm volatile(                                                   \
 261         "1:     " load "        " reg "1, [%2]\n"                       \
 262         "2:\n"                                                          \
 263         "       .section .fixup, \"ax\"\n"                              \
 264         "       .align  2\n"                                            \
 265         "3:     mov     %w0, %3\n"                                      \
 266         "       mov     %1, #0\n"                                       \
 267         "       b       2b\n"                                           \
 268         "       .previous\n"                                            \
 269         _ASM_EXTABLE(1b, 3b)                                            \
 270         : "+r" (err), "=&r" (x)                                         \
 271         : "r" (addr), "i" (-EFAULT))
 272
 273 #define __raw_get_mem(ldr, x, ptr, err)                                 \
 274 do {                                                                    \
 275         unsigned long __gu_val;                                         \
 276         switch (sizeof(*(ptr))) {                                       \
 277         case 1:                                                         \
 278                 __get_mem_asm(ldr "b", "%w", __gu_val, (ptr), (err));   \
 279                 break;                                                  \
 280         case 2:                                                         \
 281                 __get_mem_asm(ldr "h", "%w", __gu_val, (ptr), (err));   \
 282                 break;                                                  \
 283         case 4:                                                         \
 284                 __get_mem_asm(ldr, "%w", __gu_val, (ptr), (err));       \
 285                 break;                                                  \
 286         case 8:                                                         \
 287                 __get_mem_asm(ldr, "%x",  __gu_val, (ptr), (err));      \
 288                 break;                                                  \
 289         default:                                                        \
 290                 BUILD_BUG();                                            \
 291         }                                                               \
 292         (x) = (__force __typeof__(*(ptr)))__gu_val;                     \
 293 } while (0)
 294
 295 #define __raw_get_user(x, ptr, err)                                     \
 296 do {                                                                    \
 297         __chk_user_ptr(ptr);                                            \
 298         uaccess_ttbr0_enable();                                         \
 299         __raw_get_mem("ldtr", x, ptr, err);                             \
 300         uaccess_ttbr0_disable();                                        \
 301 } while (0)
 302
 303 #define __get_user_error(x, ptr, err)                                   \
 304 do {                                                                    \
 305         __typeof__(*(ptr)) __user *__p = (ptr);                         \
 306         might_fault();                                                  \
 307         if (access_ok(__p, sizeof(*__p))) {                             \
 308                 __p = uaccess_mask_ptr(__p);                            \
 309                 __raw_get_user((x), __p, (err));                        \
 310         } else {                                                        \
 311                 (x) = (__force __typeof__(x))0; (err) = -EFAULT;        \
 312         }                                                               \
 313 } while (0)
 314
 315 #define __get_user(x, ptr)                                              \
 316 ({                                                                      \
 317         int __gu_err = 0;                                               \
 318         __get_user_error((x), (ptr), __gu_err);                         \
 319         __gu_err;                                                       \
 320 })
 321
 322 #define get_user        __get_user
 323
 324 #define __get_kernel_nofault(dst, src, type, err_label)                 \
 325 do {                                                                    \
 326         int __gkn_err = 0;                                              \
 327                                                                         \
 328         __uaccess_enable_tco_async();                                   \
 329         __raw_get_mem("ldr", *((type *)(dst)),                          \
 330                       (__force type *)(src), __gkn_err);                \
 331         __uaccess_disable_tco_async();                                  \
 332         if (unlikely(__gkn_err))                                        \
 333                 goto err_label;                                         \
 334 } while (0)
 335
 336 #define __put_mem_asm(store, reg, x, addr, err)                         \
 337         asm volatile(                                                   \
 338         "1:     " store "       " reg "1, [%2]\n"                       \
 339         "2:\n"                                                          \
 340         "       .section .fixup,\"ax\"\n"                               \
 341         "       .align  2\n"                                            \
 342         "3:     mov     %w0, %3\n"                                      \
 343         "       b       2b\n"                                           \
 344         "       .previous\n"                                            \
 345         _ASM_EXTABLE(1b, 3b)                                            \
 346         : "+r" (err)                                                    \
 347         : "r" (x), "r" (addr), "i" (-EFAULT))
 348
 349 #define __raw_put_mem(str, x, ptr, err)                                 \
 350 do {                                                                    \
 351         __typeof__(*(ptr)) __pu_val = (x);                              \
 352         switch (sizeof(*(ptr))) {                                       \
 353         case 1:                                                         \
 354                 __put_mem_asm(str "b", "%w", __pu_val, (ptr), (err));   \
 355                 break;                                                  \
 356         case 2:                                                         \
 357                 __put_mem_asm(str "h", "%w", __pu_val, (ptr), (err));   \
 358                 break;                                                  \
 359         case 4:                                                         \
 360                 __put_mem_asm(str, "%w", __pu_val, (ptr), (err));       \
 361                 break;                                                  \
 362         case 8:                                                         \
 363                 __put_mem_asm(str, "%x", __pu_val, (ptr), (err));       \
 364                 break;                                                  \
 365         default:                                                        \
 366                 BUILD_BUG();                                            \
 367         }                                                               \
 368 } while (0)
 369
 370 #define __raw_put_user(x, ptr, err)                                     \
 371 do {                                                                    \
 372         __chk_user_ptr(ptr);                                            \
 373         uaccess_ttbr0_enable();                                         \
 374         __raw_put_mem("sttr", x, ptr, err);                             \
 375         uaccess_ttbr0_disable();                                        \
 376 } while (0)
 377
 378 #define __put_user_error(x, ptr, err)                                   \
 379 do {                                                                    \
 380         __typeof__(*(ptr)) __user *__p = (ptr);                         \
 381         might_fault();                                                  \
 382         if (access_ok(__p, sizeof(*__p))) {                             \
 383                 __p = uaccess_mask_ptr(__p);                            \
 384                 __raw_put_user((x), __p, (err));                        \
 385         } else  {                                                       \
 386                 (err) = -EFAULT;                                        \
 387         }                                                               \
 388 } while (0)
 389
 390 #define __put_user(x, ptr)                                              \
 391 ({                                                                      \
 392         int __pu_err = 0;                                               \
 393         __put_user_error((x), (ptr), __pu_err);                         \
 394         __pu_err;                                                       \
 395 })
 396
 397 #define put_user        __put_user
 398
 399 #define __put_kernel_nofault(dst, src, type, err_label)                 \
 400 do {                                                                    \
 401         int __pkn_err = 0;                                              \
 402                                                                         \
 403         __uaccess_enable_tco_async();                                   \
 404         __raw_put_mem("str", *((type *)(src)),                          \
 405                       (__force type *)(dst), __pkn_err);                \
 406         __uaccess_disable_tco_async();                                  \
 407         if (unlikely(__pkn_err))                                        \
 408                 goto err_label;                                         \
 409 } while(0)
 410
 411 extern unsigned long __must_check __arch_copy_from_user(void *to, const void __user *from, unsigned long n);
 412 #define raw_copy_from_user(to, from, n)                                 \
 413 ({                                                                      \
 414         unsigned long __acfu_ret;                                       \
 415         uaccess_ttbr0_enable();                                         \
 416         __acfu_ret = __arch_copy_from_user((to),                        \
 417                                       __uaccess_mask_ptr(from), (n));   \
 418         uaccess_ttbr0_disable();                                        \
 419         __acfu_ret;                                                     \
 420 })
 421
 422 extern unsigned long __must_check __arch_copy_to_user(void __user *to, const void *from, unsigned long n);
 423 #define raw_copy_to_user(to, from, n)                                   \
 424 ({                                                                      \
 425         unsigned long __actu_ret;                                       \
 426         uaccess_ttbr0_enable();                                         \
 427         __actu_ret = __arch_copy_to_user(__uaccess_mask_ptr(to),        \
 428                                     (from), (n));                       \
 429         uaccess_ttbr0_disable();                                        \
 430         __actu_ret;                                                     \
 431 })
 432
 433 #define INLINE_COPY_TO_USER
 434 #define INLINE_COPY_FROM_USER
 435
 436 extern unsigned long __must_check __arch_clear_user(void __user *to, unsigned long n);
 437 static inline unsigned long __must_check __clear_user(void __user *to, unsigned long n)
 438 {
 439         if (access_ok(to, n)) {
 440                 uaccess_ttbr0_enable();
 441                 n = __arch_clear_user(__uaccess_mask_ptr(to), n);
 442                 uaccess_ttbr0_disable();
 443         }
 444         return n;
 445 }
 446 #define clear_user      __clear_user
 447
 448 extern long strncpy_from_user(char *dest, const char __user *src, long count);
 449
 450 extern __must_check long strnlen_user(const char __user *str, long n);
 451
 452 #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
 453 struct page;
 454 void memcpy_page_flushcache(char *to, struct page *page, size_t offset, size_t len);
 455 extern unsigned long __must_check __copy_user_flushcache(void *to, const void __user *from, unsigned long n);
 456
 457 static inline int __copy_from_user_flushcache(void *dst, const void __user *src, unsigned size)
 458 {
 459         kasan_check_write(dst, size);
 460         return __copy_user_flushcache(dst, __uaccess_mask_ptr(src), size);
 461 }
 462 #endif
 463
 464 #endif /* __ASM_UACCESS_H */