arch/x86/kernel/xsave.c

   1 /*
   2  * xsave/xrstor support.
   3  *
   4  * Author: Suresh Siddha <suresh.b.siddha@intel.com>
   5  */
   6
   7 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   8
   9 #include <linux/bootmem.h>
  10 #include <linux/compat.h>
  11 #include <asm/i387.h>
  12 #include <asm/fpu-internal.h>
  13 #include <asm/sigframe.h>
  14 #include <asm/xcr.h>
  15
  16 /*
  17  * Supported feature mask by the CPU and the kernel.
  18  */
  19 u64 pcntxt_mask;
  20
  21 /*
  22  * Represents init state for the supported extended state.
  23  */
  24 struct xsave_struct *init_xstate_buf;
  25
  26 static struct _fpx_sw_bytes fx_sw_reserved, fx_sw_reserved_ia32;
  27 static unsigned int *xstate_offsets, *xstate_sizes, xstate_features;
  28
  29 /*
  30  * If a processor implementation discern that a processor state component is
  31  * in its initialized state it may modify the corresponding bit in the
  32  * xsave_hdr.xstate_bv as '0', with out modifying the corresponding memory
  33  * layout in the case of xsaveopt. While presenting the xstate information to
  34  * the user, we always ensure that the memory layout of a feature will be in
  35  * the init state if the corresponding header bit is zero. This is to ensure
  36  * that the user doesn't see some stale state in the memory layout during
  37  * signal handling, debugging etc.
  38  */
  39 void __sanitize_i387_state(struct task_struct *tsk)
  40 {
  41         struct i387_fxsave_struct *fx = &tsk->thread.fpu.state->fxsave;
  42         int feature_bit = 0x2;
  43         u64 xstate_bv;
  44
  45         if (!fx)
  46                 return;
  47
  48         xstate_bv = tsk->thread.fpu.state->xsave.xsave_hdr.xstate_bv;
  49
  50         /*
  51          * None of the feature bits are in init state. So nothing else
  52          * to do for us, as the memory layout is up to date.
  53          */
  54         if ((xstate_bv & pcntxt_mask) == pcntxt_mask)
  55                 return;
  56
  57         /*
  58          * FP is in init state
  59          */
  60         if (!(xstate_bv & XSTATE_FP)) {
  61                 fx->cwd = 0x37f;
  62                 fx->swd = 0;
  63                 fx->twd = 0;
  64                 fx->fop = 0;
  65                 fx->rip = 0;
  66                 fx->rdp = 0;
  67                 memset(&fx->st_space[0], 0, 128);
  68         }
  69
  70         /*
  71          * SSE is in init state
  72          */
  73         if (!(xstate_bv & XSTATE_SSE))
  74                 memset(&fx->xmm_space[0], 0, 256);
  75
  76         xstate_bv = (pcntxt_mask & ~xstate_bv) >> 2;
  77
  78         /*
  79          * Update all the other memory layouts for which the corresponding
  80          * header bit is in the init state.
  81          */
  82         while (xstate_bv) {
  83                 if (xstate_bv & 0x1) {
  84                         int offset = xstate_offsets[feature_bit];
  85                         int size = xstate_sizes[feature_bit];
  86
  87                         memcpy(((void *) fx) + offset,
  88                                ((void *) init_xstate_buf) + offset,
  89                                size);
  90                 }
  91
  92                 xstate_bv >>= 1;
  93                 feature_bit++;
  94         }
  95 }
  96
  97 /*
  98  * Check for the presence of extended state information in the
  99  * user fpstate pointer in the sigcontext.
 100  */
 101 static inline int check_for_xstate(struct i387_fxsave_struct __user *buf,
 102                                    void __user *fpstate,
 103                                    struct _fpx_sw_bytes *fx_sw)
 104 {
 105         int min_xstate_size = sizeof(struct i387_fxsave_struct) +
 106                               sizeof(struct xsave_hdr_struct);
 107         unsigned int magic2;
 108
 109         if (__copy_from_user(fx_sw, &buf->sw_reserved[0], sizeof(*fx_sw)))
 110                 return -1;
 111
 112         /* Check for the first magic field and other error scenarios. */
 113         if (fx_sw->magic1 != FP_XSTATE_MAGIC1 ||
 114             fx_sw->xstate_size < min_xstate_size ||
 115             fx_sw->xstate_size > xstate_size ||
 116             fx_sw->xstate_size > fx_sw->extended_size)
 117                 return -1;
 118
 119         /*
 120          * Check for the presence of second magic word at the end of memory
 121          * layout. This detects the case where the user just copied the legacy
 122          * fpstate layout with out copying the extended state information
 123          * in the memory layout.
 124          */
 125         if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size))
 126             || magic2 != FP_XSTATE_MAGIC2)
 127                 return -1;
 128
 129         return 0;
 130 }
 131
 132 /*
 133  * Signal frame handlers.
 134  */
 135 static inline int save_fsave_header(struct task_struct *tsk, void __user *buf)
 136 {
 137         if (use_fxsr()) {
 138                 struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
 139                 struct user_i387_ia32_struct env;
 140                 struct _fpstate_ia32 __user *fp = buf;
 141
 142                 convert_from_fxsr(&env, tsk);
 143
 144                 if (__copy_to_user(buf, &env, sizeof(env)) ||
 145                     __put_user(xsave->i387.swd, &fp->status) ||
 146                     __put_user(X86_FXSR_MAGIC, &fp->magic))
 147                         return -1;
 148         } else {
 149                 struct i387_fsave_struct __user *fp = buf;
 150                 u32 swd;
 151                 if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status))
 152                         return -1;
 153         }
 154
 155         return 0;
 156 }
 157
 158 static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
 159 {
 160         struct xsave_struct __user *x = buf;
 161         struct _fpx_sw_bytes *sw_bytes;
 162         u32 xstate_bv;
 163         int err;
 164
 165         /* Setup the bytes not touched by the [f]xsave and reserved for SW. */
 166         sw_bytes = ia32_frame ? &fx_sw_reserved_ia32 : &fx_sw_reserved;
 167         err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));
 168
 169         if (!use_xsave())
 170                 return err;
 171
 172         err |= __put_user(FP_XSTATE_MAGIC2, (__u32 *)(buf + xstate_size));
 173
 174         /*
 175          * Read the xstate_bv which we copied (directly from the cpu or
 176          * from the state in task struct) to the user buffers.
 177          */
 178         err |= __get_user(xstate_bv, (__u32 *)&x->xsave_hdr.xstate_bv);
 179
 180         /*
 181          * For legacy compatible, we always set FP/SSE bits in the bit
 182          * vector while saving the state to the user context. This will
 183          * enable us capturing any changes(during sigreturn) to
 184          * the FP/SSE bits by the legacy applications which don't touch
 185          * xstate_bv in the xsave header.
 186          *
 187          * xsave aware apps can change the xstate_bv in the xsave
 188          * header as well as change any contents in the memory layout.
 189          * xrestore as part of sigreturn will capture all the changes.
 190          */
 191         xstate_bv |= XSTATE_FPSSE;
 192
 193         err |= __put_user(xstate_bv, (__u32 *)&x->xsave_hdr.xstate_bv);
 194
 195         return err;
 196 }
 197
 198 static inline int save_user_xstate(struct xsave_struct __user *buf)
 199 {
 200         int err;
 201
 202         if (use_xsave())
 203                 err = xsave_user(buf);
 204         else if (use_fxsr())
 205                 err = fxsave_user((struct i387_fxsave_struct __user *) buf);
 206         else
 207                 err = fsave_user((struct i387_fsave_struct __user *) buf);
 208
 209         if (unlikely(err) && __clear_user(buf, xstate_size))
 210                 err = -EFAULT;
 211         return err;
 212 }
 213
 214 /*
 215  * Save the fpu, extended register state to the user signal frame.
 216  *
 217  * 'buf_fx' is the 64-byte aligned pointer at which the [f|fx|x]save
 218  *  state is copied.
 219  *  'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
 220  *
 221  *      buf == buf_fx for 64-bit frames and 32-bit fsave frame.
 222  *      buf != buf_fx for 32-bit frames with fxstate.
 223  *
 224  * If the fpu, extended register state is live, save the state directly
 225  * to the user frame pointed by the aligned pointer 'buf_fx'. Otherwise,
 226  * copy the thread's fpu state to the user frame starting at 'buf_fx'.
 227  *
 228  * If this is a 32-bit frame with fxstate, put a fsave header before
 229  * the aligned state at 'buf_fx'.
 230  *
 231  * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
 232  * indicating the absence/presence of the extended state to the user.
 233  */
 234 int save_xstate_sig(void __user *buf, void __user *buf_fx, int size)
 235 {
 236         struct xsave_struct *xsave = &current->thread.fpu.state->xsave;
 237         struct task_struct *tsk = current;
 238         int ia32_fxstate = (buf != buf_fx);
 239
 240         ia32_fxstate &= (config_enabled(CONFIG_X86_32) ||
 241                          config_enabled(CONFIG_IA32_EMULATION));
 242
 243         if (!access_ok(VERIFY_WRITE, buf, size))
 244                 return -EACCES;
 245
 246         if (!HAVE_HWFP)
 247                 return fpregs_soft_get(current, NULL, 0,
 248                         sizeof(struct user_i387_ia32_struct), NULL,
 249                         (struct _fpstate_ia32 __user *) buf) ? -1 : 1;
 250
 251         if (user_has_fpu()) {
 252                 /* Save the live register state to the user directly. */
 253                 if (save_user_xstate(buf_fx))
 254                         return -1;
 255                 /* Update the thread's fxstate to save the fsave header. */
 256                 if (ia32_fxstate)
 257                         fpu_fxsave(&tsk->thread.fpu);
 258         } else {
 259                 sanitize_i387_state(tsk);
 260                 if (__copy_to_user(buf_fx, xsave, xstate_size))
 261                         return -1;
 262         }
 263
 264         /* Save the fsave header for the 32-bit frames. */
 265         if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))
 266                 return -1;
 267
 268         if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
 269                 return -1;
 270
 271         drop_init_fpu(tsk);     /* trigger finit */
 272
 273         return 0;
 274 }
 275
 276 static inline void
 277 sanitize_restored_xstate(struct task_struct *tsk,
 278                          struct user_i387_ia32_struct *ia32_env,
 279                          u64 xstate_bv, int fx_only)
 280 {
 281         struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
 282         struct xsave_hdr_struct *xsave_hdr = &xsave->xsave_hdr;
 283
 284         if (use_xsave()) {
 285                 /* These bits must be zero. */
 286                 xsave_hdr->reserved1[0] = xsave_hdr->reserved1[1] = 0;
 287
 288                 /*
 289                  * Init the state that is not present in the memory
 290                  * layout and not enabled by the OS.
 291                  */
 292                 if (fx_only)
 293                         xsave_hdr->xstate_bv = XSTATE_FPSSE;
 294                 else
 295                         xsave_hdr->xstate_bv &= (pcntxt_mask & xstate_bv);
 296         }
 297
 298         if (use_fxsr()) {
 299                 /*
 300                  * mscsr reserved bits must be masked to zero for security
 301                  * reasons.
 302                  */
 303                 xsave->i387.mxcsr &= mxcsr_feature_mask;
 304
 305                 convert_to_fxsr(tsk, ia32_env);
 306         }
 307 }
 308
 309 /*
 310  * Restore the extended state if present. Otherwise, restore the FP/SSE state.
 311  */
 312 static inline int restore_user_xstate(void __user *buf, u64 xbv, int fx_only)
 313 {
 314         if (use_xsave()) {
 315                 if ((unsigned long)buf % 64 || fx_only) {
 316                         u64 init_bv = pcntxt_mask & ~XSTATE_FPSSE;
 317                         xrstor_state(init_xstate_buf, init_bv);
 318                         return fxrstor_user(buf);
 319                 } else {
 320                         u64 init_bv = pcntxt_mask & ~xbv;
 321                         if (unlikely(init_bv))
 322                                 xrstor_state(init_xstate_buf, init_bv);
 323                         return xrestore_user(buf, xbv);
 324                 }
 325         } else if (use_fxsr()) {
 326                 return fxrstor_user(buf);
 327         } else
 328                 return frstor_user(buf);
 329 }
 330
 331 int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
 332 {
 333         int ia32_fxstate = (buf != buf_fx);
 334         struct task_struct *tsk = current;
 335         int state_size = xstate_size;
 336         u64 xstate_bv = 0;
 337         int fx_only = 0;
 338
 339         ia32_fxstate &= (config_enabled(CONFIG_X86_32) ||
 340                          config_enabled(CONFIG_IA32_EMULATION));
 341
 342         if (!buf) {
 343                 drop_init_fpu(tsk);
 344                 return 0;
 345         }
 346
 347         if (!access_ok(VERIFY_READ, buf, size))
 348                 return -EACCES;
 349
 350         if (!used_math() && init_fpu(tsk))
 351                 return -1;
 352
 353         if (!HAVE_HWFP) {
 354                 return fpregs_soft_set(current, NULL,
 355                                        0, sizeof(struct user_i387_ia32_struct),
 356                                        NULL, buf) != 0;
 357         }
 358
 359         if (use_xsave()) {
 360                 struct _fpx_sw_bytes fx_sw_user;
 361                 if (unlikely(check_for_xstate(buf_fx, buf_fx, &fx_sw_user))) {
 362                         /*
 363                          * Couldn't find the extended state information in the
 364                          * memory layout. Restore just the FP/SSE and init all
 365                          * the other extended state.
 366                          */
 367                         state_size = sizeof(struct i387_fxsave_struct);
 368                         fx_only = 1;
 369                 } else {
 370                         state_size = fx_sw_user.xstate_size;
 371                         xstate_bv = fx_sw_user.xstate_bv;
 372                 }
 373         }
 374
 375         if (ia32_fxstate) {
 376                 /*
 377                  * For 32-bit frames with fxstate, copy the user state to the
 378                  * thread's fpu state, reconstruct fxstate from the fsave
 379                  * header. Sanitize the copied state etc.
 380                  */
 381                 struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
 382                 struct user_i387_ia32_struct env;
 383                 int err = 0;
 384
 385                 /*
 386                  * Drop the current fpu which clears used_math(). This ensures
 387                  * that any context-switch during the copy of the new state,
 388                  * avoids the intermediate state from getting restored/saved.
 389                  * Thus avoiding the new restored state from getting corrupted.
 390                  * We will be ready to restore/save the state only after
 391                  * set_used_math() is again set.
 392                  */
 393                 drop_fpu(tsk);
 394
 395                 if (__copy_from_user(xsave, buf_fx, state_size) ||
 396                     __copy_from_user(&env, buf, sizeof(env))) {
 397                         err = -1;
 398                 } else {
 399                         sanitize_restored_xstate(tsk, &env, xstate_bv, fx_only);
 400                         set_used_math();
 401                 }
 402
 403                 if (use_eager_fpu())
 404                         math_state_restore();
 405
 406                 return err;
 407         } else {
 408                 /*
 409                  * For 64-bit frames and 32-bit fsave frames, restore the user
 410                  * state to the registers directly (with exceptions handled).
 411                  */
 412                 user_fpu_begin();
 413                 if (restore_user_xstate(buf_fx, xstate_bv, fx_only)) {
 414                         drop_init_fpu(tsk);
 415                         return -1;
 416                 }
 417         }
 418
 419         return 0;
 420 }
 421
 422 /*
 423  * Prepare the SW reserved portion of the fxsave memory layout, indicating
 424  * the presence of the extended state information in the memory layout
 425  * pointed by the fpstate pointer in the sigcontext.
 426  * This will be saved when ever the FP and extended state context is
 427  * saved on the user stack during the signal handler delivery to the user.
 428  */
 429 static void prepare_fx_sw_frame(void)
 430 {
 431         int fsave_header_size = sizeof(struct i387_fsave_struct);
 432         int size = xstate_size + FP_XSTATE_MAGIC2_SIZE;
 433
 434         if (config_enabled(CONFIG_X86_32))
 435                 size += fsave_header_size;
 436
 437         fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
 438         fx_sw_reserved.extended_size = size;
 439         fx_sw_reserved.xstate_bv = pcntxt_mask;
 440         fx_sw_reserved.xstate_size = xstate_size;
 441
 442         if (config_enabled(CONFIG_IA32_EMULATION)) {
 443                 fx_sw_reserved_ia32 = fx_sw_reserved;
 444                 fx_sw_reserved_ia32.extended_size += fsave_header_size;
 445         }
 446 }
 447
 448 /*
 449  * Enable the extended processor state save/restore feature
 450  */
 451 static inline void xstate_enable(void)
 452 {
 453         set_in_cr4(X86_CR4_OSXSAVE);
 454         xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_mask);
 455 }
 456
 457 /*
 458  * Record the offsets and sizes of different state managed by the xsave
 459  * memory layout.
 460  */
 461 static void __init setup_xstate_features(void)
 462 {
 463         int eax, ebx, ecx, edx, leaf = 0x2;
 464
 465         xstate_features = fls64(pcntxt_mask);
 466         xstate_offsets = alloc_bootmem(xstate_features * sizeof(int));
 467         xstate_sizes = alloc_bootmem(xstate_features * sizeof(int));
 468
 469         do {
 470                 cpuid_count(XSTATE_CPUID, leaf, &eax, &ebx, &ecx, &edx);
 471
 472                 if (eax == 0)
 473                         break;
 474
 475                 xstate_offsets[leaf] = ebx;
 476                 xstate_sizes[leaf] = eax;
 477
 478                 leaf++;
 479         } while (1);
 480 }
 481
 482 /*
 483  * setup the xstate image representing the init state
 484  */
 485 static void __init setup_init_fpu_buf(void)
 486 {
 487         /*
 488          * Setup init_xstate_buf to represent the init state of
 489          * all the features managed by the xsave
 490          */
 491         init_xstate_buf = alloc_bootmem_align(xstate_size,
 492                                               __alignof__(struct xsave_struct));
 493         fx_finit(&init_xstate_buf->i387);
 494
 495         if (!cpu_has_xsave)
 496                 return;
 497
 498         setup_xstate_features();
 499
 500         /*
 501          * Init all the features state with header_bv being 0x0
 502          */
 503         xrstor_state(init_xstate_buf, -1);
 504         /*
 505          * Dump the init state again. This is to identify the init state
 506          * of any feature which is not represented by all zero's.
 507          */
 508         xsave_state(init_xstate_buf, -1);
 509 }
 510
 511 static enum { AUTO, ENABLE, DISABLE } eagerfpu = AUTO;
 512 static int __init eager_fpu_setup(char *s)
 513 {
 514         if (!strcmp(s, "on"))
 515                 eagerfpu = ENABLE;
 516         else if (!strcmp(s, "off"))
 517                 eagerfpu = DISABLE;
 518         else if (!strcmp(s, "auto"))
 519                 eagerfpu = AUTO;
 520         return 1;
 521 }
 522 __setup("eagerfpu=", eager_fpu_setup);
 523
 524 /*
 525  * Enable and initialize the xsave feature.
 526  */
 527 static void __init xstate_enable_boot_cpu(void)
 528 {
 529         unsigned int eax, ebx, ecx, edx;
 530
 531         if (boot_cpu_data.cpuid_level < XSTATE_CPUID) {
 532                 WARN(1, KERN_ERR "XSTATE_CPUID missing\n");
 533                 return;
 534         }
 535
 536         cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
 537         pcntxt_mask = eax + ((u64)edx << 32);
 538
 539         if ((pcntxt_mask & XSTATE_FPSSE) != XSTATE_FPSSE) {
 540                 pr_err("FP/SSE not shown under xsave features 0x%llx\n",
 541                        pcntxt_mask);
 542                 BUG();
 543         }
 544
 545         /*
 546          * Support only the state known to OS.
 547          */
 548         pcntxt_mask = pcntxt_mask & XCNTXT_MASK;
 549
 550         xstate_enable();
 551
 552         /*
 553          * Recompute the context size for enabled features
 554          */
 555         cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
 556         xstate_size = ebx;
 557
 558         update_regset_xstate_info(xstate_size, pcntxt_mask);
 559         prepare_fx_sw_frame();
 560         setup_init_fpu_buf();
 561
 562         /* Auto enable eagerfpu for xsaveopt */
 563         if (cpu_has_xsaveopt && eagerfpu != DISABLE)
 564                 eagerfpu = ENABLE;
 565
 566         pr_info("enabled xstate_bv 0x%llx, cntxt size 0x%x\n",
 567                 pcntxt_mask, xstate_size);
 568 }
 569
 570 /*
 571  * For the very first instance, this calls xstate_enable_boot_cpu();
 572  * for all subsequent instances, this calls xstate_enable().
 573  *
 574  * This is somewhat obfuscated due to the lack of powerful enough
 575  * overrides for the section checks.
 576  */
 577 void __cpuinit xsave_init(void)
 578 {
 579         static __refdata void (*next_func)(void) = xstate_enable_boot_cpu;
 580         void (*this_func)(void);
 581
 582         if (!cpu_has_xsave)
 583                 return;
 584
 585         this_func = next_func;
 586         next_func = xstate_enable;
 587         this_func();
 588 }
 589
 590 static inline void __init eager_fpu_init_bp(void)
 591 {
 592         current->thread.fpu.state =
 593             alloc_bootmem_align(xstate_size, __alignof__(struct xsave_struct));
 594         if (!init_xstate_buf)
 595                 setup_init_fpu_buf();
 596 }
 597
 598 void __cpuinit eager_fpu_init(void)
 599 {
 600         static __refdata void (*boot_func)(void) = eager_fpu_init_bp;
 601
 602         clear_used_math();
 603         current_thread_info()->status = 0;
 604
 605         if (eagerfpu == ENABLE)
 606                 setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
 607
 608         if (!cpu_has_eager_fpu) {
 609                 stts();
 610                 return;
 611         }
 612
 613         if (boot_func) {
 614                 boot_func();
 615                 boot_func = NULL;
 616         }
 617
 618         /*
 619          * This is same as math_state_restore(). But use_xsave() is
 620          * not yet patched to use math_state_restore().
 621          */
 622         init_fpu(current);
 623         __thread_fpu_begin(current);
 624         if (cpu_has_xsave)
 625                 xrstor_state(init_xstate_buf, -1);
 626         else
 627                 fxrstor_checking(&init_xstate_buf->i387);
 628 }