arch/x86/kernel/xsave.c

   1 /*
   2  * xsave/xrstor support.
   3  *
   4  * Author: Suresh Siddha <suresh.b.siddha@intel.com>
   5  */
   6 #include <linux/bootmem.h>
   7 #include <linux/compat.h>
   8 #include <asm/i387.h>
   9 #ifdef CONFIG_IA32_EMULATION
  10 #include <asm/sigcontext32.h>
  11 #endif
  12 #include <asm/xcr.h>
  13
  14 /*
  15  * Supported feature mask by the CPU and the kernel.
  16  */
  17 u64 pcntxt_mask;
  18
  19 /*
  20  * Represents init state for the supported extended state.
  21  */
  22 static struct xsave_struct *init_xstate_buf;
  23
  24 struct _fpx_sw_bytes fx_sw_reserved;
  25 #ifdef CONFIG_IA32_EMULATION
  26 struct _fpx_sw_bytes fx_sw_reserved_ia32;
  27 #endif
  28
  29 static unsigned int *xstate_offsets, *xstate_sizes, xstate_features;
  30
  31 /*
  32  * If a processor implementation discern that a processor state component is
  33  * in its initialized state it may modify the corresponding bit in the
  34  * xsave_hdr.xstate_bv as '0', with out modifying the corresponding memory
  35  * layout in the case of xsaveopt. While presenting the xstate information to
  36  * the user, we always ensure that the memory layout of a feature will be in
  37  * the init state if the corresponding header bit is zero. This is to ensure
  38  * that the user doesn't see some stale state in the memory layout during
  39  * signal handling, debugging etc.
  40  */
  41 void __sanitize_i387_state(struct task_struct *tsk)
  42 {
  43         u64 xstate_bv;
  44         int feature_bit = 0x2;
  45         struct i387_fxsave_struct *fx = &tsk->thread.fpu.state->fxsave;
  46
  47         if (!fx)
  48                 return;
  49
  50         BUG_ON(task_thread_info(tsk)->status & TS_USEDFPU);
  51
  52         xstate_bv = tsk->thread.fpu.state->xsave.xsave_hdr.xstate_bv;
  53
  54         /*
  55          * None of the feature bits are in init state. So nothing else
  56          * to do for us, as the memory layout is up to date.
  57          */
  58         if ((xstate_bv & pcntxt_mask) == pcntxt_mask)
  59                 return;
  60
  61         /*
  62          * FP is in init state
  63          */
  64         if (!(xstate_bv & XSTATE_FP)) {
  65                 fx->cwd = 0x37f;
  66                 fx->swd = 0;
  67                 fx->twd = 0;
  68                 fx->fop = 0;
  69                 fx->rip = 0;
  70                 fx->rdp = 0;
  71                 memset(&fx->st_space[0], 0, 128);
  72         }
  73
  74         /*
  75          * SSE is in init state
  76          */
  77         if (!(xstate_bv & XSTATE_SSE))
  78                 memset(&fx->xmm_space[0], 0, 256);
  79
  80         xstate_bv = (pcntxt_mask & ~xstate_bv) >> 2;
  81
  82         /*
  83          * Update all the other memory layouts for which the corresponding
  84          * header bit is in the init state.
  85          */
  86         while (xstate_bv) {
  87                 if (xstate_bv & 0x1) {
  88                         int offset = xstate_offsets[feature_bit];
  89                         int size = xstate_sizes[feature_bit];
  90
  91                         memcpy(((void *) fx) + offset,
  92                                ((void *) init_xstate_buf) + offset,
  93                                size);
  94                 }
  95
  96                 xstate_bv >>= 1;
  97                 feature_bit++;
  98         }
  99 }
 100
 101 /*
 102  * Check for the presence of extended state information in the
 103  * user fpstate pointer in the sigcontext.
 104  */
 105 int check_for_xstate(struct i387_fxsave_struct __user *buf,
 106                      void __user *fpstate,
 107                      struct _fpx_sw_bytes *fx_sw_user)
 108 {
 109         int min_xstate_size = sizeof(struct i387_fxsave_struct) +
 110                               sizeof(struct xsave_hdr_struct);
 111         unsigned int magic2;
 112         int err;
 113
 114         err = __copy_from_user(fx_sw_user, &buf->sw_reserved[0],
 115                                sizeof(struct _fpx_sw_bytes));
 116         if (err)
 117                 return -EFAULT;
 118
 119         /*
 120          * First Magic check failed.
 121          */
 122         if (fx_sw_user->magic1 != FP_XSTATE_MAGIC1)
 123                 return -EINVAL;
 124
 125         /*
 126          * Check for error scenarios.
 127          */
 128         if (fx_sw_user->xstate_size < min_xstate_size ||
 129             fx_sw_user->xstate_size > xstate_size ||
 130             fx_sw_user->xstate_size > fx_sw_user->extended_size)
 131                 return -EINVAL;
 132
 133         err = __get_user(magic2, (__u32 *) (((void *)fpstate) +
 134                                             fx_sw_user->extended_size -
 135                                             FP_XSTATE_MAGIC2_SIZE));
 136         if (err)
 137                 return err;
 138         /*
 139          * Check for the presence of second magic word at the end of memory
 140          * layout. This detects the case where the user just copied the legacy
 141          * fpstate layout with out copying the extended state information
 142          * in the memory layout.
 143          */
 144         if (magic2 != FP_XSTATE_MAGIC2)
 145                 return -EFAULT;
 146
 147         return 0;
 148 }
 149
 150 #ifdef CONFIG_X86_64
 151 /*
 152  * Signal frame handlers.
 153  */
 154
 155 int save_i387_xstate(void __user *buf)
 156 {
 157         struct task_struct *tsk = current;
 158         int err = 0;
 159
 160         if (!access_ok(VERIFY_WRITE, buf, sig_xstate_size))
 161                 return -EACCES;
 162
 163         BUG_ON(sig_xstate_size < xstate_size);
 164
 165         if ((unsigned long)buf % 64)
 166                 printk("save_i387_xstate: bad fpstate %p\n", buf);
 167
 168         if (!used_math())
 169                 return 0;
 170
 171         if (user_has_fpu()) {
 172                 if (use_xsave())
 173                         err = xsave_user(buf);
 174                 else
 175                         err = fxsave_user(buf);
 176
 177                 if (err)
 178                         return err;
 179                 user_fpu_end();
 180         } else {
 181                 sanitize_i387_state(tsk);
 182                 if (__copy_to_user(buf, &tsk->thread.fpu.state->fxsave,
 183                                    xstate_size))
 184                         return -1;
 185         }
 186
 187         clear_used_math(); /* trigger finit */
 188
 189         if (use_xsave()) {
 190                 struct _fpstate __user *fx = buf;
 191                 struct _xstate __user *x = buf;
 192                 u64 xstate_bv;
 193
 194                 err = __copy_to_user(&fx->sw_reserved, &fx_sw_reserved,
 195                                      sizeof(struct _fpx_sw_bytes));
 196
 197                 err |= __put_user(FP_XSTATE_MAGIC2,
 198                                   (__u32 __user *) (buf + sig_xstate_size
 199                                                     - FP_XSTATE_MAGIC2_SIZE));
 200
 201                 /*
 202                  * Read the xstate_bv which we copied (directly from the cpu or
 203                  * from the state in task struct) to the user buffers and
 204                  * set the FP/SSE bits.
 205                  */
 206                 err |= __get_user(xstate_bv, &x->xstate_hdr.xstate_bv);
 207
 208                 /*
 209                  * For legacy compatible, we always set FP/SSE bits in the bit
 210                  * vector while saving the state to the user context. This will
 211                  * enable us capturing any changes(during sigreturn) to
 212                  * the FP/SSE bits by the legacy applications which don't touch
 213                  * xstate_bv in the xsave header.
 214                  *
 215                  * xsave aware apps can change the xstate_bv in the xsave
 216                  * header as well as change any contents in the memory layout.
 217                  * xrestore as part of sigreturn will capture all the changes.
 218                  */
 219                 xstate_bv |= XSTATE_FPSSE;
 220
 221                 err |= __put_user(xstate_bv, &x->xstate_hdr.xstate_bv);
 222
 223                 if (err)
 224                         return err;
 225         }
 226
 227         return 1;
 228 }
 229
 230 /*
 231  * Restore the extended state if present. Otherwise, restore the FP/SSE
 232  * state.
 233  */
 234 static int restore_user_xstate(void __user *buf)
 235 {
 236         struct _fpx_sw_bytes fx_sw_user;
 237         u64 mask;
 238         int err;
 239
 240         if (((unsigned long)buf % 64) ||
 241              check_for_xstate(buf, buf, &fx_sw_user))
 242                 goto fx_only;
 243
 244         mask = fx_sw_user.xstate_bv;
 245
 246         /*
 247          * restore the state passed by the user.
 248          */
 249         err = xrestore_user(buf, mask);
 250         if (err)
 251                 return err;
 252
 253         /*
 254          * init the state skipped by the user.
 255          */
 256         mask = pcntxt_mask & ~mask;
 257         if (unlikely(mask))
 258                 xrstor_state(init_xstate_buf, mask);
 259
 260         return 0;
 261
 262 fx_only:
 263         /*
 264          * couldn't find the extended state information in the
 265          * memory layout. Restore just the FP/SSE and init all
 266          * the other extended state.
 267          */
 268         xrstor_state(init_xstate_buf, pcntxt_mask & ~XSTATE_FPSSE);
 269         return fxrstor_checking((__force struct i387_fxsave_struct *)buf);
 270 }
 271
 272 /*
 273  * This restores directly out of user space. Exceptions are handled.
 274  */
 275 int restore_i387_xstate(void __user *buf)
 276 {
 277         struct task_struct *tsk = current;
 278         int err = 0;
 279
 280         if (!buf) {
 281                 if (used_math())
 282                         goto clear;
 283                 return 0;
 284         } else
 285                 if (!access_ok(VERIFY_READ, buf, sig_xstate_size))
 286                         return -EACCES;
 287
 288         if (!used_math()) {
 289                 err = init_fpu(tsk);
 290                 if (err)
 291                         return err;
 292         }
 293
 294         user_fpu_begin();
 295         if (use_xsave())
 296                 err = restore_user_xstate(buf);
 297         else
 298                 err = fxrstor_checking((__force struct i387_fxsave_struct *)
 299                                        buf);
 300         if (unlikely(err)) {
 301                 /*
 302                  * Encountered an error while doing the restore from the
 303                  * user buffer, clear the fpu state.
 304                  */
 305 clear:
 306                 clear_fpu(tsk);
 307                 clear_used_math();
 308         }
 309         return err;
 310 }
 311 #endif
 312
 313 /*
 314  * Prepare the SW reserved portion of the fxsave memory layout, indicating
 315  * the presence of the extended state information in the memory layout
 316  * pointed by the fpstate pointer in the sigcontext.
 317  * This will be saved when ever the FP and extended state context is
 318  * saved on the user stack during the signal handler delivery to the user.
 319  */
 320 static void prepare_fx_sw_frame(void)
 321 {
 322         int size_extended = (xstate_size - sizeof(struct i387_fxsave_struct)) +
 323                              FP_XSTATE_MAGIC2_SIZE;
 324
 325         sig_xstate_size = sizeof(struct _fpstate) + size_extended;
 326
 327 #ifdef CONFIG_IA32_EMULATION
 328         sig_xstate_ia32_size = sizeof(struct _fpstate_ia32) + size_extended;
 329 #endif
 330
 331         memset(&fx_sw_reserved, 0, sizeof(fx_sw_reserved));
 332
 333         fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
 334         fx_sw_reserved.extended_size = sig_xstate_size;
 335         fx_sw_reserved.xstate_bv = pcntxt_mask;
 336         fx_sw_reserved.xstate_size = xstate_size;
 337 #ifdef CONFIG_IA32_EMULATION
 338         memcpy(&fx_sw_reserved_ia32, &fx_sw_reserved,
 339                sizeof(struct _fpx_sw_bytes));
 340         fx_sw_reserved_ia32.extended_size = sig_xstate_ia32_size;
 341 #endif
 342 }
 343
 344 #ifdef CONFIG_X86_64
 345 unsigned int sig_xstate_size = sizeof(struct _fpstate);
 346 #endif
 347
 348 /*
 349  * Enable the extended processor state save/restore feature
 350  */
 351 static inline void xstate_enable(void)
 352 {
 353         set_in_cr4(X86_CR4_OSXSAVE);
 354         xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_mask);
 355 }
 356
 357 /*
 358  * Record the offsets and sizes of different state managed by the xsave
 359  * memory layout.
 360  */
 361 static void __init setup_xstate_features(void)
 362 {
 363         int eax, ebx, ecx, edx, leaf = 0x2;
 364
 365         xstate_features = fls64(pcntxt_mask);
 366         xstate_offsets = alloc_bootmem(xstate_features * sizeof(int));
 367         xstate_sizes = alloc_bootmem(xstate_features * sizeof(int));
 368
 369         do {
 370                 cpuid_count(XSTATE_CPUID, leaf, &eax, &ebx, &ecx, &edx);
 371
 372                 if (eax == 0)
 373                         break;
 374
 375                 xstate_offsets[leaf] = ebx;
 376                 xstate_sizes[leaf] = eax;
 377
 378                 leaf++;
 379         } while (1);
 380 }
 381
 382 /*
 383  * setup the xstate image representing the init state
 384  */
 385 static void __init setup_xstate_init(void)
 386 {
 387         setup_xstate_features();
 388
 389         /*
 390          * Setup init_xstate_buf to represent the init state of
 391          * all the features managed by the xsave
 392          */
 393         init_xstate_buf = alloc_bootmem_align(xstate_size,
 394                                               __alignof__(struct xsave_struct));
 395         init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;
 396
 397         clts();
 398         /*
 399          * Init all the features state with header_bv being 0x0
 400          */
 401         xrstor_state(init_xstate_buf, -1);
 402         /*
 403          * Dump the init state again. This is to identify the init state
 404          * of any feature which is not represented by all zero's.
 405          */
 406         xsave_state(init_xstate_buf, -1);
 407         stts();
 408 }
 409
 410 /*
 411  * Enable and initialize the xsave feature.
 412  */
 413 static void __init xstate_enable_boot_cpu(void)
 414 {
 415         unsigned int eax, ebx, ecx, edx;
 416
 417         if (boot_cpu_data.cpuid_level < XSTATE_CPUID) {
 418                 WARN(1, KERN_ERR "XSTATE_CPUID missing\n");
 419                 return;
 420         }
 421
 422         cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
 423         pcntxt_mask = eax + ((u64)edx << 32);
 424
 425         if ((pcntxt_mask & XSTATE_FPSSE) != XSTATE_FPSSE) {
 426                 printk(KERN_ERR "FP/SSE not shown under xsave features 0x%llx\n",
 427                        pcntxt_mask);
 428                 BUG();
 429         }
 430
 431         /*
 432          * Support only the state known to OS.
 433          */
 434         pcntxt_mask = pcntxt_mask & XCNTXT_MASK;
 435
 436         xstate_enable();
 437
 438         /*
 439          * Recompute the context size for enabled features
 440          */
 441         cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
 442         xstate_size = ebx;
 443
 444         update_regset_xstate_info(xstate_size, pcntxt_mask);
 445         prepare_fx_sw_frame();
 446
 447         setup_xstate_init();
 448
 449         printk(KERN_INFO "xsave/xrstor: enabled xstate_bv 0x%llx, "
 450                "cntxt size 0x%x\n",
 451                pcntxt_mask, xstate_size);
 452 }
 453
 454 /*
 455  * For the very first instance, this calls xstate_enable_boot_cpu();
 456  * for all subsequent instances, this calls xstate_enable().
 457  *
 458  * This is somewhat obfuscated due to the lack of powerful enough
 459  * overrides for the section checks.
 460  */
 461 void __cpuinit xsave_init(void)
 462 {
 463         static __refdata void (*next_func)(void) = xstate_enable_boot_cpu;
 464         void (*this_func)(void);
 465
 466         if (!cpu_has_xsave)
 467                 return;
 468
 469         this_func = next_func;
 470         next_func = xstate_enable;
 471         this_func();
 472 }