root/arch/x86/kernel/fpu/signal.c

DEFINITIONS

1. check_for_xstate
2. save_fsave_header
3. save_xstate_epilog
4. copy_fpregs_to_sigframe
5. copy_fpstate_to_sigframe
6. sanitize_restored_xstate
7. copy_user_to_fpregs_zeroing
8. __fpu__restore_sig
9. xstate_sigframe_size
10. fpu__restore_sig
11. fpu__alloc_mathframe
12. fpu__init_prepare_fx_sw_frame

   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 (!access_ok(buf, size))
 174                 return -EACCES;
 175 
 176         if (!static_cpu_has(X86_FEATURE_FPU))
 177                 return fpregs_soft_get(current, NULL, 0,
 178                         sizeof(struct user_i387_ia32_struct), NULL,
 179                         (struct _fpstate_32 __user *) buf) ? -1 : 1;
 180 
 181 retry:
 182         /*
 183          * Load the FPU registers if they are not valid for the current task.
 184          * With a valid FPU state we can attempt to save the state directly to
 185          * userland's stack frame which will likely succeed. If it does not,
 186          * resolve the fault in the user memory and try again.
 187          */
 188         fpregs_lock();
 189         if (test_thread_flag(TIF_NEED_FPU_LOAD))
 190                 __fpregs_load_activate();
 191 
 192         pagefault_disable();
 193         ret = copy_fpregs_to_sigframe(buf_fx);
 194         pagefault_enable();
 195         fpregs_unlock();
 196 
 197         if (ret) {
 198                 if (!fault_in_pages_writeable(buf_fx, fpu_user_xstate_size))
 199                         goto retry;
 200                 return -EFAULT;
 201         }
 202 
 203         /* Save the fsave header for the 32-bit frames. */
 204         if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))
 205                 return -1;
 206 
 207         if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
 208                 return -1;
 209 
 210         return 0;
 211 }
 212 
 213 static inline void
 214 sanitize_restored_xstate(union fpregs_state *state,
 215                          struct user_i387_ia32_struct *ia32_env,
 216                          u64 xfeatures, int fx_only)
 217 {
 218         struct xregs_state *xsave = &state->xsave;
 219         struct xstate_header *header = &xsave->header;
 220 
 221         if (use_xsave()) {
 222                 /*
 223                  * Note: we don't need to zero the reserved bits in the
 224                  * xstate_header here because we either didn't copy them at all,
 225                  * or we checked earlier that they aren't set.
 226                  */
 227 
 228                 /*
 229                  * Init the state that is not present in the memory
 230                  * layout and not enabled by the OS.
 231                  */
 232                 if (fx_only)
 233                         header->xfeatures = XFEATURE_MASK_FPSSE;
 234                 else
 235                         header->xfeatures &= xfeatures;
 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         if (use_xsave()) {
 256                 if (fx_only) {
 257                         u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
 258                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 259                         return copy_user_to_fxregs(buf);
 260                 } else {
 261                         u64 init_bv = xfeatures_mask & ~xbv;
 262                         if (unlikely(init_bv))
 263                                 copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 264                         return copy_user_to_xregs(buf, xbv);
 265                 }
 266         } else if (use_fxsr()) {
 267                 return copy_user_to_fxregs(buf);
 268         } else
 269                 return copy_user_to_fregs(buf);
 270 }
 271 
 272 static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 273 {
 274         struct user_i387_ia32_struct *envp = NULL;
 275         int state_size = fpu_kernel_xstate_size;
 276         int ia32_fxstate = (buf != buf_fx);
 277         struct task_struct *tsk = current;
 278         struct fpu *fpu = &tsk->thread.fpu;
 279         struct user_i387_ia32_struct env;
 280         u64 xfeatures = 0;
 281         int fx_only = 0;
 282         int ret = 0;
 283 
 284         ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
 285                          IS_ENABLED(CONFIG_IA32_EMULATION));
 286 
 287         if (!buf) {
 288                 fpu__clear(fpu);
 289                 return 0;
 290         }
 291 
 292         if (!access_ok(buf, size))
 293                 return -EACCES;
 294 
 295         if (!static_cpu_has(X86_FEATURE_FPU))
 296                 return fpregs_soft_set(current, NULL,
 297                                        0, sizeof(struct user_i387_ia32_struct),
 298                                        NULL, buf) != 0;
 299 
 300         if (use_xsave()) {
 301                 struct _fpx_sw_bytes fx_sw_user;
 302                 if (unlikely(check_for_xstate(buf_fx, buf_fx, &fx_sw_user))) {
 303                         /*
 304                          * Couldn't find the extended state information in the
 305                          * memory layout. Restore just the FP/SSE and init all
 306                          * the other extended state.
 307                          */
 308                         state_size = sizeof(struct fxregs_state);
 309                         fx_only = 1;
 310                         trace_x86_fpu_xstate_check_failed(fpu);
 311                 } else {
 312                         state_size = fx_sw_user.xstate_size;
 313                         xfeatures = fx_sw_user.xfeatures;
 314                 }
 315         }
 316 
 317         /*
 318          * The current state of the FPU registers does not matter. By setting
 319          * TIF_NEED_FPU_LOAD unconditionally it is ensured that the our xstate
 320          * is not modified on context switch and that the xstate is considered
 321          * to be loaded again on return to userland (overriding last_cpu avoids
 322          * the optimisation).
 323          */
 324         set_thread_flag(TIF_NEED_FPU_LOAD);
 325         __fpu_invalidate_fpregs_state(fpu);
 326 
 327         if ((unsigned long)buf_fx % 64)
 328                 fx_only = 1;
 329         /*
 330          * For 32-bit frames with fxstate, copy the fxstate so it can be
 331          * reconstructed later.
 332          */
 333         if (ia32_fxstate) {
 334                 ret = __copy_from_user(&env, buf, sizeof(env));
 335                 if (ret)
 336                         goto err_out;
 337                 envp = &env;
 338         } else {
 339                 /*
 340                  * Attempt to restore the FPU registers directly from user
 341                  * memory. For that to succeed, the user access cannot cause
 342                  * page faults. If it does, fall back to the slow path below,
 343                  * going through the kernel buffer with the enabled pagefault
 344                  * handler.
 345                  */
 346                 fpregs_lock();
 347                 pagefault_disable();
 348                 ret = copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only);
 349                 pagefault_enable();
 350                 if (!ret) {
 351                         fpregs_mark_activate();
 352                         fpregs_unlock();
 353                         return 0;
 354                 }
 355                 fpregs_deactivate(fpu);
 356                 fpregs_unlock();
 357         }
 358 
 359 
 360         if (use_xsave() && !fx_only) {
 361                 u64 init_bv = xfeatures_mask & ~xfeatures;
 362 
 363                 if (using_compacted_format()) {
 364                         ret = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
 365                 } else {
 366                         ret = __copy_from_user(&fpu->state.xsave, buf_fx, state_size);
 367 
 368                         if (!ret && state_size > offsetof(struct xregs_state, header))
 369                                 ret = validate_xstate_header(&fpu->state.xsave.header);
 370                 }
 371                 if (ret)
 372                         goto err_out;
 373 
 374                 sanitize_restored_xstate(&fpu->state, envp, xfeatures, fx_only);
 375 
 376                 fpregs_lock();
 377                 if (unlikely(init_bv))
 378                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 379                 ret = copy_kernel_to_xregs_err(&fpu->state.xsave, xfeatures);
 380 
 381         } else if (use_fxsr()) {
 382                 ret = __copy_from_user(&fpu->state.fxsave, buf_fx, state_size);
 383                 if (ret) {
 384                         ret = -EFAULT;
 385                         goto err_out;
 386                 }
 387 
 388                 sanitize_restored_xstate(&fpu->state, envp, xfeatures, fx_only);
 389 
 390                 fpregs_lock();
 391                 if (use_xsave()) {
 392                         u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
 393                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 394                 }
 395 
 396                 ret = copy_kernel_to_fxregs_err(&fpu->state.fxsave);
 397         } else {
 398                 ret = __copy_from_user(&fpu->state.fsave, buf_fx, state_size);
 399                 if (ret)
 400                         goto err_out;
 401 
 402                 fpregs_lock();
 403                 ret = copy_kernel_to_fregs_err(&fpu->state.fsave);
 404         }
 405         if (!ret)
 406                 fpregs_mark_activate();
 407         else
 408                 fpregs_deactivate(fpu);
 409         fpregs_unlock();
 410 
 411 err_out:
 412         if (ret)
 413                 fpu__clear(fpu);
 414         return ret;
 415 }
 416 
 417 static inline int xstate_sigframe_size(void)
 418 {
 419         return use_xsave() ? fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE :
 420                         fpu_user_xstate_size;
 421 }
 422 
 423 /*
 424  * Restore FPU state from a sigframe:
 425  */
 426 int fpu__restore_sig(void __user *buf, int ia32_frame)
 427 {
 428         void __user *buf_fx = buf;
 429         int size = xstate_sigframe_size();
 430 
 431         if (ia32_frame && use_fxsr()) {
 432                 buf_fx = buf + sizeof(struct fregs_state);
 433                 size += sizeof(struct fregs_state);
 434         }
 435 
 436         return __fpu__restore_sig(buf, buf_fx, size);
 437 }
 438 
 439 unsigned long
 440 fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
 441                      unsigned long *buf_fx, unsigned long *size)
 442 {
 443         unsigned long frame_size = xstate_sigframe_size();
 444 
 445         *buf_fx = sp = round_down(sp - frame_size, 64);
 446         if (ia32_frame && use_fxsr()) {
 447                 frame_size += sizeof(struct fregs_state);
 448                 sp -= sizeof(struct fregs_state);
 449         }
 450 
 451         *size = frame_size;
 452 
 453         return sp;
 454 }
 455 /*
 456  * Prepare the SW reserved portion of the fxsave memory layout, indicating
 457  * the presence of the extended state information in the memory layout
 458  * pointed by the fpstate pointer in the sigcontext.
 459  * This will be saved when ever the FP and extended state context is
 460  * saved on the user stack during the signal handler delivery to the user.
 461  */
 462 void fpu__init_prepare_fx_sw_frame(void)
 463 {
 464         int size = fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE;
 465 
 466         fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
 467         fx_sw_reserved.extended_size = size;
 468         fx_sw_reserved.xfeatures = xfeatures_mask;
 469         fx_sw_reserved.xstate_size = fpu_user_xstate_size;
 470 
 471         if (IS_ENABLED(CONFIG_IA32_EMULATION) ||
 472             IS_ENABLED(CONFIG_X86_32)) {
 473                 int fsave_header_size = sizeof(struct fregs_state);
 474 
 475                 fx_sw_reserved_ia32 = fx_sw_reserved;
 476                 fx_sw_reserved_ia32.extended_size = size + fsave_header_size;
 477         }
 478 }
 479