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
   9 #include <asm/fpu/internal.h>
  10 #include <asm/fpu/signal.h>
  11 #include <asm/fpu/regset.h>
  12 #include <asm/fpu/xstate.h>
  13
  14 #include <asm/sigframe.h>
  15 #include <asm/trace/fpu.h>
  16
  17 static struct _fpx_sw_bytes fx_sw_reserved, fx_sw_reserved_ia32;
  18
  19 /*
  20  * Check for the presence of extended state information in the
  21  * user fpstate pointer in the sigcontext.
  22  */
  23 static inline int check_for_xstate(struct fxregs_state __user *buf,
  24                                    void __user *fpstate,
  25                                    struct _fpx_sw_bytes *fx_sw)
  26 {
  27         int min_xstate_size = sizeof(struct fxregs_state) +
  28                               sizeof(struct xstate_header);
  29         unsigned int magic2;
  30
  31         if (__copy_from_user(fx_sw, &buf->sw_reserved[0], sizeof(*fx_sw)))
  32                 return -1;
  33
  34         /* Check for the first magic field and other error scenarios. */
  35         if (fx_sw->magic1 != FP_XSTATE_MAGIC1 ||
  36             fx_sw->xstate_size < min_xstate_size ||
  37             fx_sw->xstate_size > fpu_user_xstate_size ||
  38             fx_sw->xstate_size > fx_sw->extended_size)
  39                 return -1;
  40
  41         /*
  42          * Check for the presence of second magic word at the end of memory
  43          * layout. This detects the case where the user just copied the legacy
  44          * fpstate layout with out copying the extended state information
  45          * in the memory layout.
  46          */
  47         if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size))
  48             || magic2 != FP_XSTATE_MAGIC2)
  49                 return -1;
  50
  51         return 0;
  52 }
  53
  54 /*
  55  * Signal frame handlers.
  56  */
  57 static inline int save_fsave_header(struct task_struct *tsk, void __user *buf)
  58 {
  59         if (use_fxsr()) {
  60                 struct xregs_state *xsave = &tsk->thread.fpu.state.xsave;
  61                 struct user_i387_ia32_struct env;
  62                 struct _fpstate_32 __user *fp = buf;
  63
  64                 convert_from_fxsr(&env, tsk);
  65
  66                 if (__copy_to_user(buf, &env, sizeof(env)) ||
  67                     __put_user(xsave->i387.swd, &fp->status) ||
  68                     __put_user(X86_FXSR_MAGIC, &fp->magic))
  69                         return -1;
  70         } else {
  71                 struct fregs_state __user *fp = buf;
  72                 u32 swd;
  73                 if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status))
  74                         return -1;
  75         }
  76
  77         return 0;
  78 }
  79
  80 static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
  81 {
  82         struct xregs_state __user *x = buf;
  83         struct _fpx_sw_bytes *sw_bytes;
  84         u32 xfeatures;
  85         int err;
  86
  87         /* Setup the bytes not touched by the [f]xsave and reserved for SW. */
  88         sw_bytes = ia32_frame ? &fx_sw_reserved_ia32 : &fx_sw_reserved;
  89         err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));
  90
  91         if (!use_xsave())
  92                 return err;
  93
  94         err |= __put_user(FP_XSTATE_MAGIC2,
  95                           (__u32 __user *)(buf + fpu_user_xstate_size));
  96
  97         /*
  98          * Read the xfeatures which we copied (directly from the cpu or
  99          * from the state in task struct) to the user buffers.
 100          */
 101         err |= __get_user(xfeatures, (__u32 __user *)&x->header.xfeatures);
 102
 103         /*
 104          * For legacy compatible, we always set FP/SSE bits in the bit
 105          * vector while saving the state to the user context. This will
 106          * enable us capturing any changes(during sigreturn) to
 107          * the FP/SSE bits by the legacy applications which don't touch
 108          * xfeatures in the xsave header.
 109          *
 110          * xsave aware apps can change the xfeatures in the xsave
 111          * header as well as change any contents in the memory layout.
 112          * xrestore as part of sigreturn will capture all the changes.
 113          */
 114         xfeatures |= XFEATURE_MASK_FPSSE;
 115
 116         err |= __put_user(xfeatures, (__u32 __user *)&x->header.xfeatures);
 117
 118         return err;
 119 }
 120
 121 static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
 122 {
 123         int err;
 124
 125         if (use_xsave())
 126                 err = copy_xregs_to_user(buf);
 127         else if (use_fxsr())
 128                 err = copy_fxregs_to_user((struct fxregs_state __user *) buf);
 129         else
 130                 err = copy_fregs_to_user((struct fregs_state __user *) buf);
 131
 132         if (unlikely(err) && __clear_user(buf, fpu_user_xstate_size))
 133                 err = -EFAULT;
 134         return err;
 135 }
 136
 137 /*
 138  * Save the fpu, extended register state to the user signal frame.
 139  *
 140  * 'buf_fx' is the 64-byte aligned pointer at which the [f|fx|x]save
 141  *  state is copied.
 142  *  'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
 143  *
 144  *      buf == buf_fx for 64-bit frames and 32-bit fsave frame.
 145  *      buf != buf_fx for 32-bit frames with fxstate.
 146  *
 147  * Try to save it directly to the user frame with disabled page fault handler.
 148  * If this fails then do the slow path where the FPU state is first saved to
 149  * task's fpu->state and then copy it to the user frame pointed to by the
 150  * aligned pointer 'buf_fx'.
 151  *
 152  * If this is a 32-bit frame with fxstate, put a fsave header before
 153  * the aligned state at 'buf_fx'.
 154  *
 155  * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
 156  * indicating the absence/presence of the extended state to the user.
 157  */
 158 int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 159 {
 160         struct task_struct *tsk = current;
 161         int ia32_fxstate = (buf != buf_fx);
 162         int ret;
 163
 164         ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
 165                          IS_ENABLED(CONFIG_IA32_EMULATION));
 166
 167         if (!access_ok(buf, size))
 168                 return -EACCES;
 169
 170         if (!static_cpu_has(X86_FEATURE_FPU))
 171                 return fpregs_soft_get(current, NULL, 0,
 172                         sizeof(struct user_i387_ia32_struct), NULL,
 173                         (struct _fpstate_32 __user *) buf) ? -1 : 1;
 174
 175 retry:
 176         /*
 177          * Load the FPU registers if they are not valid for the current task.
 178          * With a valid FPU state we can attempt to save the state directly to
 179          * userland's stack frame which will likely succeed. If it does not,
 180          * resolve the fault in the user memory and try again.
 181          */
 182         fpregs_lock();
 183         if (test_thread_flag(TIF_NEED_FPU_LOAD))
 184                 __fpregs_load_activate();
 185
 186         pagefault_disable();
 187         ret = copy_fpregs_to_sigframe(buf_fx);
 188         pagefault_enable();
 189         fpregs_unlock();
 190
 191         if (ret) {
 192                 int aligned_size;
 193                 int nr_pages;
 194
 195                 aligned_size = offset_in_page(buf_fx) + fpu_user_xstate_size;
 196                 nr_pages = DIV_ROUND_UP(aligned_size, PAGE_SIZE);
 197
 198                 ret = get_user_pages_unlocked((unsigned long)buf_fx, nr_pages,
 199                                               NULL, FOLL_WRITE);
 200                 if (ret == nr_pages)
 201                         goto retry;
 202                 return -EFAULT;
 203         }
 204
 205         /* Save the fsave header for the 32-bit frames. */
 206         if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))
 207                 return -1;
 208
 209         if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
 210                 return -1;
 211
 212         return 0;
 213 }
 214
 215 static inline void
 216 sanitize_restored_xstate(union fpregs_state *state,
 217                          struct user_i387_ia32_struct *ia32_env,
 218                          u64 xfeatures, int fx_only)
 219 {
 220         struct xregs_state *xsave = &state->xsave;
 221         struct xstate_header *header = &xsave->header;
 222
 223         if (use_xsave()) {
 224                 /*
 225                  * Note: we don't need to zero the reserved bits in the
 226                  * xstate_header here because we either didn't copy them at all,
 227                  * or we checked earlier that they aren't set.
 228                  */
 229
 230                 /*
 231                  * Init the state that is not present in the memory
 232                  * layout and not enabled by the OS.
 233                  */
 234                 if (fx_only)
 235                         header->xfeatures = XFEATURE_MASK_FPSSE;
 236                 else
 237                         header->xfeatures &= xfeatures;
 238         }
 239
 240         if (use_fxsr()) {
 241                 /*
 242                  * mscsr reserved bits must be masked to zero for security
 243                  * reasons.
 244                  */
 245                 xsave->i387.mxcsr &= mxcsr_feature_mask;
 246
 247                 if (ia32_env)
 248                         convert_to_fxsr(&state->fxsave, ia32_env);
 249         }
 250 }
 251
 252 /*
 253  * Restore the extended state if present. Otherwise, restore the FP/SSE state.
 254  */
 255 static int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only)
 256 {
 257         if (use_xsave()) {
 258                 if (fx_only) {
 259                         u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
 260                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 261                         return copy_user_to_fxregs(buf);
 262                 } else {
 263                         u64 init_bv = xfeatures_mask & ~xbv;
 264                         if (unlikely(init_bv))
 265                                 copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 266                         return copy_user_to_xregs(buf, xbv);
 267                 }
 268         } else if (use_fxsr()) {
 269                 return copy_user_to_fxregs(buf);
 270         } else
 271                 return copy_user_to_fregs(buf);
 272 }
 273
 274 static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 275 {
 276         struct user_i387_ia32_struct *envp = NULL;
 277         int state_size = fpu_kernel_xstate_size;
 278         int ia32_fxstate = (buf != buf_fx);
 279         struct task_struct *tsk = current;
 280         struct fpu *fpu = &tsk->thread.fpu;
 281         struct user_i387_ia32_struct env;
 282         u64 xfeatures = 0;
 283         int fx_only = 0;
 284         int ret = 0;
 285
 286         ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
 287                          IS_ENABLED(CONFIG_IA32_EMULATION));
 288
 289         if (!buf) {
 290                 fpu__clear(fpu);
 291                 return 0;
 292         }
 293
 294         if (!access_ok(buf, size))
 295                 return -EACCES;
 296
 297         if (!static_cpu_has(X86_FEATURE_FPU))
 298                 return fpregs_soft_set(current, NULL,
 299                                        0, sizeof(struct user_i387_ia32_struct),
 300                                        NULL, buf) != 0;
 301
 302         if (use_xsave()) {
 303                 struct _fpx_sw_bytes fx_sw_user;
 304                 if (unlikely(check_for_xstate(buf_fx, buf_fx, &fx_sw_user))) {
 305                         /*
 306                          * Couldn't find the extended state information in the
 307                          * memory layout. Restore just the FP/SSE and init all
 308                          * the other extended state.
 309                          */
 310                         state_size = sizeof(struct fxregs_state);
 311                         fx_only = 1;
 312                         trace_x86_fpu_xstate_check_failed(fpu);
 313                 } else {
 314                         state_size = fx_sw_user.xstate_size;
 315                         xfeatures = fx_sw_user.xfeatures;
 316                 }
 317         }
 318
 319         /*
 320          * The current state of the FPU registers does not matter. By setting
 321          * TIF_NEED_FPU_LOAD unconditionally it is ensured that the our xstate
 322          * is not modified on context switch and that the xstate is considered
 323          * to be loaded again on return to userland (overriding last_cpu avoids
 324          * the optimisation).
 325          */
 326         set_thread_flag(TIF_NEED_FPU_LOAD);
 327         __fpu_invalidate_fpregs_state(fpu);
 328
 329         if ((unsigned long)buf_fx % 64)
 330                 fx_only = 1;
 331         /*
 332          * For 32-bit frames with fxstate, copy the fxstate so it can be
 333          * reconstructed later.
 334          */
 335         if (ia32_fxstate) {
 336                 ret = __copy_from_user(&env, buf, sizeof(env));
 337                 if (ret)
 338                         goto err_out;
 339                 envp = &env;
 340         } else {
 341                 /*
 342                  * Attempt to restore the FPU registers directly from user
 343                  * memory. For that to succeed, the user access cannot cause
 344                  * page faults. If it does, fall back to the slow path below,
 345                  * going through the kernel buffer with the enabled pagefault
 346                  * handler.
 347                  */
 348                 fpregs_lock();
 349                 pagefault_disable();
 350                 ret = copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only);
 351                 pagefault_enable();
 352                 if (!ret) {
 353                         fpregs_mark_activate();
 354                         fpregs_unlock();
 355                         return 0;
 356                 }
 357                 fpregs_unlock();
 358         }
 359
 360
 361         if (use_xsave() && !fx_only) {
 362                 u64 init_bv = xfeatures_mask & ~xfeatures;
 363
 364                 if (using_compacted_format()) {
 365                         ret = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
 366                 } else {
 367                         ret = __copy_from_user(&fpu->state.xsave, buf_fx, state_size);
 368
 369                         if (!ret && state_size > offsetof(struct xregs_state, header))
 370                                 ret = validate_xstate_header(&fpu->state.xsave.header);
 371                 }
 372                 if (ret)
 373                         goto err_out;
 374
 375                 sanitize_restored_xstate(&fpu->state, envp, xfeatures, fx_only);
 376
 377                 fpregs_lock();
 378                 if (unlikely(init_bv))
 379                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 380                 ret = copy_kernel_to_xregs_err(&fpu->state.xsave, xfeatures);
 381
 382         } else if (use_fxsr()) {
 383                 ret = __copy_from_user(&fpu->state.fxsave, buf_fx, state_size);
 384                 if (ret) {
 385                         ret = -EFAULT;
 386                         goto err_out;
 387                 }
 388
 389                 sanitize_restored_xstate(&fpu->state, envp, xfeatures, fx_only);
 390
 391                 fpregs_lock();
 392                 if (use_xsave()) {
 393                         u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
 394                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 395                 }
 396
 397                 ret = copy_kernel_to_fxregs_err(&fpu->state.fxsave);
 398         } else {
 399                 ret = __copy_from_user(&fpu->state.fsave, buf_fx, state_size);
 400                 if (ret)
 401                         goto err_out;
 402
 403                 fpregs_lock();
 404                 ret = copy_kernel_to_fregs_err(&fpu->state.fsave);
 405         }
 406         if (!ret)
 407                 fpregs_mark_activate();
 408         fpregs_unlock();
 409
 410 err_out:
 411         if (ret)
 412                 fpu__clear(fpu);
 413         return ret;
 414 }
 415
 416 static inline int xstate_sigframe_size(void)
 417 {
 418         return use_xsave() ? fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE :
 419                         fpu_user_xstate_size;
 420 }
 421
 422 /*
 423  * Restore FPU state from a sigframe:
 424  */
 425 int fpu__restore_sig(void __user *buf, int ia32_frame)
 426 {
 427         void __user *buf_fx = buf;
 428         int size = xstate_sigframe_size();
 429
 430         if (ia32_frame && use_fxsr()) {
 431                 buf_fx = buf + sizeof(struct fregs_state);
 432                 size += sizeof(struct fregs_state);
 433         }
 434
 435         return __fpu__restore_sig(buf, buf_fx, size);
 436 }
 437
 438 unsigned long
 439 fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
 440                      unsigned long *buf_fx, unsigned long *size)
 441 {
 442         unsigned long frame_size = xstate_sigframe_size();
 443
 444         *buf_fx = sp = round_down(sp - frame_size, 64);
 445         if (ia32_frame && use_fxsr()) {
 446                 frame_size += sizeof(struct fregs_state);
 447                 sp -= sizeof(struct fregs_state);
 448         }
 449
 450         *size = frame_size;
 451
 452         return sp;
 453 }
 454 /*
 455  * Prepare the SW reserved portion of the fxsave memory layout, indicating
 456  * the presence of the extended state information in the memory layout
 457  * pointed by the fpstate pointer in the sigcontext.
 458  * This will be saved when ever the FP and extended state context is
 459  * saved on the user stack during the signal handler delivery to the user.
 460  */
 461 void fpu__init_prepare_fx_sw_frame(void)
 462 {
 463         int size = fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE;
 464
 465         fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
 466         fx_sw_reserved.extended_size = size;
 467         fx_sw_reserved.xfeatures = xfeatures_mask;
 468         fx_sw_reserved.xstate_size = fpu_user_xstate_size;
 469
 470         if (IS_ENABLED(CONFIG_IA32_EMULATION) ||
 471             IS_ENABLED(CONFIG_X86_32)) {
 472                 int fsave_header_size = sizeof(struct fregs_state);
 473
 474                 fx_sw_reserved_ia32 = fx_sw_reserved;
 475                 fx_sw_reserved_ia32.extended_size = size + fsave_header_size;
 476         }
 477 }
 478