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 *)(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 *)&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 *)&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  * If the fpu, extended register state is live, save the state directly
 148  * to the user frame pointed by the aligned pointer 'buf_fx'. Otherwise,
 149  * copy the thread's fpu state to the user frame starting at 'buf_fx'.
 150  *
 151  * If this is a 32-bit frame with fxstate, put a fsave header before
 152  * the aligned state at 'buf_fx'.
 153  *
 154  * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
 155  * indicating the absence/presence of the extended state to the user.
 156  */
 157 int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 158 {
 159         struct fpu *fpu = &current->thread.fpu;
 160         struct xregs_state *xsave = &fpu->state.xsave;
 161         struct task_struct *tsk = current;
 162         int ia32_fxstate = (buf != buf_fx);
 163
 164         ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
 165                          IS_ENABLED(CONFIG_IA32_EMULATION));
 166
 167         if (!access_ok(VERIFY_WRITE, 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         if (fpu->initialized || using_compacted_format()) {
 176                 /* Save the live register state to the user directly. */
 177                 if (copy_fpregs_to_sigframe(buf_fx))
 178                         return -1;
 179                 /* Update the thread's fxstate to save the fsave header. */
 180                 if (ia32_fxstate)
 181                         copy_fxregs_to_kernel(fpu);
 182         } else {
 183                 /*
 184                  * It is a *bug* if kernel uses compacted-format for xsave
 185                  * area and we copy it out directly to a signal frame. It
 186                  * should have been handled above by saving the registers
 187                  * directly.
 188                  */
 189                 if (boot_cpu_has(X86_FEATURE_XSAVES)) {
 190                         WARN_ONCE(1, "x86/fpu: saving compacted-format xsave area to a signal frame!\n");
 191                         return -1;
 192                 }
 193
 194                 fpstate_sanitize_xstate(fpu);
 195                 if (__copy_to_user(buf_fx, xsave, fpu_user_xstate_size))
 196                         return -1;
 197         }
 198
 199         /* Save the fsave header for the 32-bit frames. */
 200         if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))
 201                 return -1;
 202
 203         if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
 204                 return -1;
 205
 206         return 0;
 207 }
 208
 209 static inline void
 210 sanitize_restored_xstate(struct task_struct *tsk,
 211                          struct user_i387_ia32_struct *ia32_env,
 212                          u64 xfeatures, int fx_only)
 213 {
 214         struct xregs_state *xsave = &tsk->thread.fpu.state.xsave;
 215         struct xstate_header *header = &xsave->header;
 216
 217         if (use_xsave()) {
 218                 /*
 219                  * Note: we don't need to zero the reserved bits in the
 220                  * xstate_header here because we either didn't copy them at all,
 221                  * or we checked earlier that they aren't set.
 222                  */
 223
 224                 /*
 225                  * Init the state that is not present in the memory
 226                  * layout and not enabled by the OS.
 227                  */
 228                 if (fx_only)
 229                         header->xfeatures = XFEATURE_MASK_FPSSE;
 230                 else
 231                         header->xfeatures &= xfeatures;
 232         }
 233
 234         if (use_fxsr()) {
 235                 /*
 236                  * mscsr reserved bits must be masked to zero for security
 237                  * reasons.
 238                  */
 239                 xsave->i387.mxcsr &= mxcsr_feature_mask;
 240
 241                 convert_to_fxsr(tsk, ia32_env);
 242         }
 243 }
 244
 245 /*
 246  * Restore the extended state if present. Otherwise, restore the FP/SSE state.
 247  */
 248 static inline int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only)
 249 {
 250         if (use_xsave()) {
 251                 if ((unsigned long)buf % 64 || fx_only) {
 252                         u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
 253                         copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 254                         return copy_user_to_fxregs(buf);
 255                 } else {
 256                         u64 init_bv = xfeatures_mask & ~xbv;
 257                         if (unlikely(init_bv))
 258                                 copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
 259                         return copy_user_to_xregs(buf, xbv);
 260                 }
 261         } else if (use_fxsr()) {
 262                 return copy_user_to_fxregs(buf);
 263         } else
 264                 return copy_user_to_fregs(buf);
 265 }
 266
 267 static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 268 {
 269         int ia32_fxstate = (buf != buf_fx);
 270         struct task_struct *tsk = current;
 271         struct fpu *fpu = &tsk->thread.fpu;
 272         int state_size = fpu_kernel_xstate_size;
 273         u64 xfeatures = 0;
 274         int fx_only = 0;
 275
 276         ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
 277                          IS_ENABLED(CONFIG_IA32_EMULATION));
 278
 279         if (!buf) {
 280                 fpu__clear(fpu);
 281                 return 0;
 282         }
 283
 284         if (!access_ok(VERIFY_READ, buf, size))
 285                 return -EACCES;
 286
 287         fpu__initialize(fpu);
 288
 289         if (!static_cpu_has(X86_FEATURE_FPU))
 290                 return fpregs_soft_set(current, NULL,
 291                                        0, sizeof(struct user_i387_ia32_struct),
 292                                        NULL, buf) != 0;
 293
 294         if (use_xsave()) {
 295                 struct _fpx_sw_bytes fx_sw_user;
 296                 if (unlikely(check_for_xstate(buf_fx, buf_fx, &fx_sw_user))) {
 297                         /*
 298                          * Couldn't find the extended state information in the
 299                          * memory layout. Restore just the FP/SSE and init all
 300                          * the other extended state.
 301                          */
 302                         state_size = sizeof(struct fxregs_state);
 303                         fx_only = 1;
 304                         trace_x86_fpu_xstate_check_failed(fpu);
 305                 } else {
 306                         state_size = fx_sw_user.xstate_size;
 307                         xfeatures = fx_sw_user.xfeatures;
 308                 }
 309         }
 310
 311         if (ia32_fxstate) {
 312                 /*
 313                  * For 32-bit frames with fxstate, copy the user state to the
 314                  * thread's fpu state, reconstruct fxstate from the fsave
 315                  * header. Validate and sanitize the copied state.
 316                  */
 317                 struct user_i387_ia32_struct env;
 318                 int err = 0;
 319
 320                 /*
 321                  * Drop the current fpu which clears fpu->initialized. This ensures
 322                  * that any context-switch during the copy of the new state,
 323                  * avoids the intermediate state from getting restored/saved.
 324                  * Thus avoiding the new restored state from getting corrupted.
 325                  * We will be ready to restore/save the state only after
 326                  * fpu->initialized is again set.
 327                  */
 328                 fpu__drop(fpu);
 329
 330                 if (using_compacted_format()) {
 331                         err = copy_user_to_xstate(&fpu->state.xsave, buf_fx);
 332                 } else {
 333                         err = __copy_from_user(&fpu->state.xsave, buf_fx, state_size);
 334
 335                         if (!err && state_size > offsetof(struct xregs_state, header))
 336                                 err = validate_xstate_header(&fpu->state.xsave.header);
 337                 }
 338
 339                 if (err || __copy_from_user(&env, buf, sizeof(env))) {
 340                         fpstate_init(&fpu->state);
 341                         trace_x86_fpu_init_state(fpu);
 342                         err = -1;
 343                 } else {
 344                         sanitize_restored_xstate(tsk, &env, xfeatures, fx_only);
 345                 }
 346
 347                 fpu->initialized = 1;
 348                 preempt_disable();
 349                 fpu__restore(fpu);
 350                 preempt_enable();
 351
 352                 return err;
 353         } else {
 354                 /*
 355                  * For 64-bit frames and 32-bit fsave frames, restore the user
 356                  * state to the registers directly (with exceptions handled).
 357                  */
 358                 user_fpu_begin();
 359                 if (copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only)) {
 360                         fpu__clear(fpu);
 361                         return -1;
 362                 }
 363         }
 364
 365         return 0;
 366 }
 367
 368 static inline int xstate_sigframe_size(void)
 369 {
 370         return use_xsave() ? fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE :
 371                         fpu_user_xstate_size;
 372 }
 373
 374 /*
 375  * Restore FPU state from a sigframe:
 376  */
 377 int fpu__restore_sig(void __user *buf, int ia32_frame)
 378 {
 379         void __user *buf_fx = buf;
 380         int size = xstate_sigframe_size();
 381
 382         if (ia32_frame && use_fxsr()) {
 383                 buf_fx = buf + sizeof(struct fregs_state);
 384                 size += sizeof(struct fregs_state);
 385         }
 386
 387         return __fpu__restore_sig(buf, buf_fx, size);
 388 }
 389
 390 unsigned long
 391 fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
 392                      unsigned long *buf_fx, unsigned long *size)
 393 {
 394         unsigned long frame_size = xstate_sigframe_size();
 395
 396         *buf_fx = sp = round_down(sp - frame_size, 64);
 397         if (ia32_frame && use_fxsr()) {
 398                 frame_size += sizeof(struct fregs_state);
 399                 sp -= sizeof(struct fregs_state);
 400         }
 401
 402         *size = frame_size;
 403
 404         return sp;
 405 }
 406 /*
 407  * Prepare the SW reserved portion of the fxsave memory layout, indicating
 408  * the presence of the extended state information in the memory layout
 409  * pointed by the fpstate pointer in the sigcontext.
 410  * This will be saved when ever the FP and extended state context is
 411  * saved on the user stack during the signal handler delivery to the user.
 412  */
 413 void fpu__init_prepare_fx_sw_frame(void)
 414 {
 415         int size = fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE;
 416
 417         fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
 418         fx_sw_reserved.extended_size = size;
 419         fx_sw_reserved.xfeatures = xfeatures_mask;
 420         fx_sw_reserved.xstate_size = fpu_user_xstate_size;
 421
 422         if (IS_ENABLED(CONFIG_IA32_EMULATION) ||
 423             IS_ENABLED(CONFIG_X86_32)) {
 424                 int fsave_header_size = sizeof(struct fregs_state);
 425
 426                 fx_sw_reserved_ia32 = fx_sw_reserved;
 427                 fx_sw_reserved_ia32.extended_size = size + fsave_header_size;
 428         }
 429 }
 430