arch/x86/kernel/fpu/signal.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * FPU signal frame handling routines.
   4  */
   5
   6 #include <linux/compat.h>
   7 #include <linux/cpu.h>
   8 #include <linux/pagemap.h>
   9
  10 #include <asm/fpu/internal.h>
  11 #include <asm/fpu/signal.h>
  12 #include <asm/fpu/regset.h>
  13 #include <asm/fpu/xstate.h>
  14
  15 #include <asm/sigframe.h>
  16 #include <asm/trace/fpu.h>
  17
  18 static struct _fpx_sw_bytes fx_sw_reserved, fx_sw_reserved_ia32;
  19
  20 /*
  21  * Check for the presence of extended state information in the
  22  * user fpstate pointer in the sigcontext.
  23  */
  24 static inline int check_for_xstate(struct fxregs_state __user *buf,
  25                                    void __user *fpstate,
  26                                    struct _fpx_sw_bytes *fx_sw)
  27 {
  28         int min_xstate_size = sizeof(struct fxregs_state) +
  29                               sizeof(struct xstate_header);
  30         unsigned int magic2;
  31
  32         if (__copy_from_user(fx_sw, &buf->sw_reserved[0], sizeof(*fx_sw)))
  33                 return -1;
  34
  35         /* Check for the first magic field and other error scenarios. */
  36         if (fx_sw->magic1 != FP_XSTATE_MAGIC1 ||
  37             fx_sw->xstate_size < min_xstate_size ||
  38             fx_sw->xstate_size > fpu_user_xstate_size ||
  39             fx_sw->xstate_size > fx_sw->extended_size)
  40                 return -1;
  41
  42         /*
  43          * Check for the presence of second magic word at the end of memory
  44          * layout. This detects the case where the user just copied the legacy
  45          * fpstate layout with out copying the extended state information
  46          * in the memory layout.
  47          */
  48         if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size))
  49             || magic2 != FP_XSTATE_MAGIC2)
  50                 return -1;
  51
  52         return 0;
  53 }
  54
  55 /*
  56  * Signal frame handlers.
  57  */
  58 static inline int save_fsave_header(struct task_struct *tsk, void __user *buf)
  59 {
  60         if (use_fxsr()) {
  61                 struct xregs_state *xsave = &tsk->thread.fpu.state.xsave;
  62                 struct user_i387_ia32_struct env;
  63                 struct _fpstate_32 __user *fp = buf;
  64
  65                 fpregs_lock();
  66                 if (!test_thread_flag(TIF_NEED_FPU_LOAD))
  67                         copy_fxregs_to_kernel(&tsk->thread.fpu);
  68                 fpregs_unlock();
  69
  70                 convert_from_fxsr(&env, tsk);
  71
  72                 if (__copy_to_user(buf, &env, sizeof(env)) ||
  73                     __put_user(xsave->i387.swd, &fp->status) ||
  74                     __put_user(X86_FXSR_MAGIC, &fp->magic))
  75                         return -1;
  76         } else {
  77                 struct fregs_state __user *fp = buf;
  78                 u32 swd;
  79                 if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status))
  80                         return -1;
  81         }
  82
  83         return 0;
  84 }
  85
  86 static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
  87 {
  88         struct xregs_state __user *x = buf;
  89         struct _fpx_sw_bytes *sw_bytes;
  90         u32 xfeatures;
  91         int err;
  92
  93         /* Setup the bytes not touched by the [f]xsave and reserved for SW. */
  94         sw_bytes = ia32_frame ? &fx_sw_reserved_ia32 : &fx_sw_reserved;
  95         err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));
  96
  97         if (!use_xsave())
  98                 return err;
  99
 100         err |= __put_user(FP_XSTATE_MAGIC2,
 101                           (__u32 __user *)(buf + fpu_user_xstate_size));
 102
 103         /*
 104          * Read the xfeatures which we copied (directly from the cpu or
 105          * from the state in task struct) to the user buffers.
 106          */
 107         err |= __get_user(xfeatures, (__u32 __user *)&x->header.xfeatures);
 108
 109         /*
 110          * For legacy compatible, we always set FP/SSE bits in the bit
 111          * vector while saving the state to the user context. This will
 112          * enable us capturing any changes(during sigreturn) to
 113          * the FP/SSE bits by the legacy applications which don't touch
 114          * xfeatures in the xsave header.
 115          *
 116          * xsave aware apps can change the xfeatures in the xsave
 117          * header as well as change any contents in the memory layout.
 118          * xrestore as part of sigreturn will capture all the changes.
 119          */
 120         xfeatures |= XFEATURE_MASK_FPSSE;
 121
 122         err |= __put_user(xfeatures, (__u32 __user *)&x->header.xfeatures);
 123
 124         return err;
 125 }
 126
 127 static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
 128 {
 129         int err;
 130
 131         if (use_xsave())
 132                 err = copy_xregs_to_user(buf);
 133         else if (use_fxsr())
 134                 err = copy_fxregs_to_user((struct fxregs_state __user *) buf);
 135         else
 136                 err = copy_fregs_to_user((struct fregs_state __user *) buf);
 137
 138         if (unlikely(err) && __clear_user(buf, fpu_user_xstate_size))
 139                 err = -EFAULT;
 140         return err;
 141 }
 142
 143 /*
 144  * Save the fpu, extended register state to the user signal frame.
 145  *
 146  * 'buf_fx' is the 64-byte aligned pointer at which the [f|fx|x]save
 147  *  state is copied.
 148  *  'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
 149  *
 150  *      buf == buf_fx for 64-bit frames and 32-bit fsave frame.
 151  *      buf != buf_fx for 32-bit frames with fxstate.
 152  *
 153  * Try to save it directly to the user frame with disabled page fault handler.
 154  * If this fails then do the slow path where the FPU state is first saved to
 155  * task's fpu->state and then copy it to the user frame pointed to by the
 156  * aligned pointer 'buf_fx'.
 157  *
 158  * If this is a 32-bit frame with fxstate, put a fsave header before
 159  * the aligned state at 'buf_fx'.
 160  *
 161  * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
 162  * indicating the absence/presence of the extended state to the user.
 163  */
 164 int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 165 {
 166         struct task_struct *tsk = current;
 167         int ia32_fxstate = (buf != buf_fx);
 168         int ret;
 169
 170         ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
 171                          IS_ENABLED(CONFIG_IA32_EMULATION));
 172
 173         if (!static_cpu_has(X86_FEATURE_FPU)) {
 174                 struct user_i387_ia32_struct fp;
 175                 fpregs_soft_get(current, NULL, (struct membuf){.p = &fp,
 176                                                 .left = sizeof(fp)});
 177                 return copy_to_user(buf, &fp, sizeof(fp)) ? -EFAULT : 0;
 178         }
 179
 180         if (!access_ok(buf, size))
 181                 return -EACCES;
 182 retry:
 183         /*
 184          * Load the FPU registers if they are not valid for the current task.
 185          * With a valid FPU state we can attempt to save the state directly to
 186          * userland's stack frame which will likely succeed. If it does not,
 187          * resolve the fault in the user memory and try again.
 188          */
 189         fpregs_lock();
 190         if (test_thread_flag(TIF_NEED_FPU_LOAD))
 191                 __fpregs_load_activate();
 192
 193         pagefault_disable();
 194         ret = copy_fpregs_to_sigframe(buf_fx);
 195         pagefault_enable();
 196         fpregs_unlock();
 197
 198         if (ret) {
 199                 if (!fault_in_pages_writeable(buf_fx, fpu_user_xstate_size))
 200                         goto retry;
 201                 return -EFAULT;
 202         }
 203
 204         /* Save the fsave header for the 32-bit frames. */
 205         if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))
 206                 return -1;
 207
 208         if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
 209                 return -1;
 210
 211         return 0;
 212 }
 213
 214 static inline void
 215 sanitize_restored_user_xstate(union fpregs_state *state,
 216                               struct user_i387_ia32_struct *ia32_env,
 217                               u64 user_xfeatures, int fx_only)
 218 {
 219         struct xregs_state *xsave = &state->xsave;
 220         struct xstate_header *header = &xsave->header;
 221
 222         if (use_xsave()) {
 223                 /*
 224                  * Clear all feature bits which are not set in
 225                  * user_xfeatures and clear all extended features
 226                  * for fx_only mode.
 227                  */
 228                 u64 mask = fx_only ? XFEATURE_MASK_FPSSE : user_xfeatures;
 229
 230                 /*
 231                  * Supervisor state has to be preserved. The sigframe
 232                  * restore can only modify user features, i.e. @mask
 233                  * cannot contain them.
 234                  */
 235                 header->xfeatures &= mask | xfeatures_mask_supervisor();
 236         }
 237
 238         if (use_fxsr()) {
 239                 /*
 240                  * mscsr reserved bits must be masked to zero for security
 241                  * reasons.
 242                  */
 243                 xsave->i387.mxcsr &= mxcsr_feature_mask;
 244
 245                 if (ia32_env)
 246                         convert_to_fxsr(&state->fxsave, ia32_env);
 247         }
 248 }
 249
 250 /*
 251  * Restore the extended state if present. Otherwise, restore the FP/SSE state.
 252  */
 253 static int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only)
 254 {
 255         u64 init_bv;
 256         int r;
 257
 258         if (use_xsave()) {
 259                 if (fx_only) {
 260                         init_bv = xfeatures_mask_user() & ~XFEATURE_MASK_FPSSE;
 261
 262                         r = copy_user_to_fxregs(buf);
 263                         if (!r)
 264                                 copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 265                         return r;
 266                 } else {
 267                         init_bv = xfeatures_mask_user() & ~xbv;
 268
 269                         r = copy_user_to_xregs(buf, xbv);
 270                         if (!r && unlikely(init_bv))
 271                                 copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 272                         return r;
 273                 }
 274         } else if (use_fxsr()) {
 275                 return copy_user_to_fxregs(buf);
 276         } else
 277                 return copy_user_to_fregs(buf);
 278 }
 279
 280 static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 281 {
 282         struct user_i387_ia32_struct *envp = NULL;
 283         int state_size = fpu_kernel_xstate_size;
 284         int ia32_fxstate = (buf != buf_fx);
 285         struct task_struct *tsk = current;
 286         struct fpu *fpu = &tsk->thread.fpu;
 287         struct user_i387_ia32_struct env;
 288         u64 user_xfeatures = 0;
 289         int fx_only = 0;
 290         int ret = 0;
 291
 292         ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
 293                          IS_ENABLED(CONFIG_IA32_EMULATION));
 294
 295         if (!buf) {
 296                 fpu__clear_user_states(fpu);
 297                 return 0;
 298         }
 299
 300         if (!access_ok(buf, size)) {
 301                 ret = -EACCES;
 302                 goto out;
 303         }
 304
 305         if (!static_cpu_has(X86_FEATURE_FPU)) {
 306                 ret = fpregs_soft_set(current, NULL, 0,
 307                                       sizeof(struct user_i387_ia32_struct),
 308                                       NULL, buf);
 309                 goto out;
 310         }
 311
 312         if (use_xsave()) {
 313                 struct _fpx_sw_bytes fx_sw_user;
 314                 if (unlikely(check_for_xstate(buf_fx, buf_fx, &fx_sw_user))) {
 315                         /*
 316                          * Couldn't find the extended state information in the
 317                          * memory layout. Restore just the FP/SSE and init all
 318                          * the other extended state.
 319                          */
 320                         state_size = sizeof(struct fxregs_state);
 321                         fx_only = 1;
 322                         trace_x86_fpu_xstate_check_failed(fpu);
 323                 } else {
 324                         state_size = fx_sw_user.xstate_size;
 325                         user_xfeatures = fx_sw_user.xfeatures;
 326                 }
 327         }
 328
 329         if ((unsigned long)buf_fx % 64)
 330                 fx_only = 1;
 331
 332         if (!ia32_fxstate) {
 333                 /*
 334                  * Attempt to restore the FPU registers directly from user
 335                  * memory. For that to succeed, the user access cannot cause
 336                  * page faults. If it does, fall back to the slow path below,
 337                  * going through the kernel buffer with the enabled pagefault
 338                  * handler.
 339                  */
 340                 fpregs_lock();
 341                 pagefault_disable();
 342                 ret = copy_user_to_fpregs_zeroing(buf_fx, user_xfeatures, fx_only);
 343                 pagefault_enable();
 344                 if (!ret) {
 345
 346                         /*
 347                          * Restore supervisor states: previous context switch
 348                          * etc has done XSAVES and saved the supervisor states
 349                          * in the kernel buffer from which they can be restored
 350                          * now.
 351                          *
 352                          * We cannot do a single XRSTORS here - which would
 353                          * be nice - because the rest of the FPU registers are
 354                          * being restored from a user buffer directly. The
 355                          * single XRSTORS happens below, when the user buffer
 356                          * has been copied to the kernel one.
 357                          */
 358                         if (test_thread_flag(TIF_NEED_FPU_LOAD) &&
 359                             xfeatures_mask_supervisor())
 360                                 copy_kernel_to_xregs(&fpu->state.xsave,
 361                                                      xfeatures_mask_supervisor());
 362                         fpregs_mark_activate();
 363                         fpregs_unlock();
 364                         return 0;
 365                 }
 366
 367                 /*
 368                  * The above did an FPU restore operation, restricted to
 369                  * the user portion of the registers, and failed, but the
 370                  * microcode might have modified the FPU registers
 371                  * nevertheless.
 372                  *
 373                  * If the FPU registers do not belong to current, then
 374                  * invalidate the FPU register state otherwise the task might
 375                  * preempt current and return to user space with corrupted
 376                  * FPU registers.
 377                  *
 378                  * In case current owns the FPU registers then no further
 379                  * action is required. The fixup below will handle it
 380                  * correctly.
 381                  */
 382                 if (test_thread_flag(TIF_NEED_FPU_LOAD))
 383                         __cpu_invalidate_fpregs_state();
 384
 385                 fpregs_unlock();
 386         } else {
 387                 /*
 388                  * For 32-bit frames with fxstate, copy the fxstate so it can
 389                  * be reconstructed later.
 390                  */
 391                 ret = __copy_from_user(&env, buf, sizeof(env));
 392                 if (ret)
 393                         goto out;
 394                 envp = &env;
 395         }
 396
 397         /*
 398          * By setting TIF_NEED_FPU_LOAD it is ensured that our xstate is
 399          * not modified on context switch and that the xstate is considered
 400          * to be loaded again on return to userland (overriding last_cpu avoids
 401          * the optimisation).
 402          */
 403         fpregs_lock();
 404         if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
 405                 /*
 406                  * If supervisor states are available then save the
 407                  * hardware state in current's fpstate so that the
 408                  * supervisor state is preserved. Save the full state for
 409                  * simplicity. There is no point in optimizing this by only
 410                  * saving the supervisor states and then shuffle them to
 411                  * the right place in memory. This is the slow path and the
 412                  * above XRSTOR failed or ia32_fxstate is true. Shrug.
 413                  */
 414                 if (xfeatures_mask_supervisor())
 415                         copy_xregs_to_kernel(&fpu->state.xsave);
 416                 set_thread_flag(TIF_NEED_FPU_LOAD);
 417         }
 418         __fpu_invalidate_fpregs_state(fpu);
 419         fpregs_unlock();
 420
 421         if (use_xsave() && !fx_only) {
 422                 u64 init_bv = xfeatures_mask_user() & ~user_xfeatures;
 423
 424                 ret = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
 425                 if (ret)
 426                         goto out;
 427
 428                 sanitize_restored_user_xstate(&fpu->state, envp, user_xfeatures,
 429                                               fx_only);
 430
 431                 fpregs_lock();
 432                 if (unlikely(init_bv))
 433                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 434
 435                 /*
 436                  * Restore previously saved supervisor xstates along with
 437                  * copied-in user xstates.
 438                  */
 439                 ret = copy_kernel_to_xregs_err(&fpu->state.xsave,
 440                                                user_xfeatures | xfeatures_mask_supervisor());
 441
 442         } else if (use_fxsr()) {
 443                 ret = __copy_from_user(&fpu->state.fxsave, buf_fx, state_size);
 444                 if (ret) {
 445                         ret = -EFAULT;
 446                         goto out;
 447                 }
 448
 449                 sanitize_restored_user_xstate(&fpu->state, envp, user_xfeatures,
 450                                               fx_only);
 451
 452                 fpregs_lock();
 453                 if (use_xsave()) {
 454                         u64 init_bv;
 455
 456                         init_bv = xfeatures_mask_user() & ~XFEATURE_MASK_FPSSE;
 457                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 458                 }
 459
 460                 ret = copy_kernel_to_fxregs_err(&fpu->state.fxsave);
 461         } else {
 462                 ret = __copy_from_user(&fpu->state.fsave, buf_fx, state_size);
 463                 if (ret)
 464                         goto out;
 465
 466                 fpregs_lock();
 467                 ret = copy_kernel_to_fregs_err(&fpu->state.fsave);
 468         }
 469         if (!ret)
 470                 fpregs_mark_activate();
 471         else
 472                 fpregs_deactivate(fpu);
 473         fpregs_unlock();
 474
 475 out:
 476         if (ret)
 477                 fpu__clear_user_states(fpu);
 478         return ret;
 479 }
 480
 481 static inline int xstate_sigframe_size(void)
 482 {
 483         return use_xsave() ? fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE :
 484                         fpu_user_xstate_size;
 485 }
 486
 487 /*
 488  * Restore FPU state from a sigframe:
 489  */
 490 int fpu__restore_sig(void __user *buf, int ia32_frame)
 491 {
 492         void __user *buf_fx = buf;
 493         int size = xstate_sigframe_size();
 494
 495         if (ia32_frame && use_fxsr()) {
 496                 buf_fx = buf + sizeof(struct fregs_state);
 497                 size += sizeof(struct fregs_state);
 498         }
 499
 500         return __fpu__restore_sig(buf, buf_fx, size);
 501 }
 502
 503 unsigned long
 504 fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
 505                      unsigned long *buf_fx, unsigned long *size)
 506 {
 507         unsigned long frame_size = xstate_sigframe_size();
 508
 509         *buf_fx = sp = round_down(sp - frame_size, 64);
 510         if (ia32_frame && use_fxsr()) {
 511                 frame_size += sizeof(struct fregs_state);
 512                 sp -= sizeof(struct fregs_state);
 513         }
 514
 515         *size = frame_size;
 516
 517         return sp;
 518 }
 519
 520 unsigned long fpu__get_fpstate_size(void)
 521 {
 522         unsigned long ret = xstate_sigframe_size();
 523
 524         /*
 525          * This space is needed on (most) 32-bit kernels, or when a 32-bit
 526          * app is running on a 64-bit kernel. To keep things simple, just
 527          * assume the worst case and always include space for 'freg_state',
 528          * even for 64-bit apps on 64-bit kernels. This wastes a bit of
 529          * space, but keeps the code simple.
 530          */
 531         if ((IS_ENABLED(CONFIG_IA32_EMULATION) ||
 532              IS_ENABLED(CONFIG_X86_32)) && use_fxsr())
 533                 ret += sizeof(struct fregs_state);
 534
 535         return ret;
 536 }
 537
 538 /*
 539  * Prepare the SW reserved portion of the fxsave memory layout, indicating
 540  * the presence of the extended state information in the memory layout
 541  * pointed by the fpstate pointer in the sigcontext.
 542  * This will be saved when ever the FP and extended state context is
 543  * saved on the user stack during the signal handler delivery to the user.
 544  */
 545 void fpu__init_prepare_fx_sw_frame(void)
 546 {
 547         int size = fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE;
 548
 549         fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
 550         fx_sw_reserved.extended_size = size;
 551         fx_sw_reserved.xfeatures = xfeatures_mask_user();
 552         fx_sw_reserved.xstate_size = fpu_user_xstate_size;
 553
 554         if (IS_ENABLED(CONFIG_IA32_EMULATION) ||
 555             IS_ENABLED(CONFIG_X86_32)) {
 556                 int fsave_header_size = sizeof(struct fregs_state);
 557
 558                 fx_sw_reserved_ia32 = fx_sw_reserved;
 559                 fx_sw_reserved_ia32.extended_size = size + fsave_header_size;
 560         }
 561 }
 562