arch/x86/kernel/fpu/regset.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * FPU register's regset abstraction, for ptrace, core dumps, etc.
   4  */
   5 #include <linux/sched/task_stack.h>
   6 #include <linux/vmalloc.h>
   7
   8 #include <asm/fpu/internal.h>
   9 #include <asm/fpu/signal.h>
  10 #include <asm/fpu/regset.h>
  11 #include <asm/fpu/xstate.h>
  12
  13 #include "context.h"
  14 #include "internal.h"
  15
  16 /*
  17  * The xstateregs_active() routine is the same as the regset_fpregs_active() routine,
  18  * as the "regset->n" for the xstate regset will be updated based on the feature
  19  * capabilities supported by the xsave.
  20  */
  21 int regset_fpregs_active(struct task_struct *target, const struct user_regset *regset)
  22 {
  23         return regset->n;
  24 }
  25
  26 int regset_xregset_fpregs_active(struct task_struct *target, const struct user_regset *regset)
  27 {
  28         if (boot_cpu_has(X86_FEATURE_FXSR))
  29                 return regset->n;
  30         else
  31                 return 0;
  32 }
  33
  34 /*
  35  * The regset get() functions are invoked from:
  36  *
  37  *   - coredump to dump the current task's fpstate. If the current task
  38  *     owns the FPU then the memory state has to be synchronized and the
  39  *     FPU register state preserved. Otherwise fpstate is already in sync.
  40  *
  41  *   - ptrace to dump fpstate of a stopped task, in which case the registers
  42  *     have already been saved to fpstate on context switch.
  43  */
  44 static void sync_fpstate(struct fpu *fpu)
  45 {
  46         if (fpu == &current->thread.fpu)
  47                 fpu_sync_fpstate(fpu);
  48 }
  49
  50 /*
  51  * Invalidate cached FPU registers before modifying the stopped target
  52  * task's fpstate.
  53  *
  54  * This forces the target task on resume to restore the FPU registers from
  55  * modified fpstate. Otherwise the task might skip the restore and operate
  56  * with the cached FPU registers which discards the modifications.
  57  */
  58 static void fpu_force_restore(struct fpu *fpu)
  59 {
  60         /*
  61          * Only stopped child tasks can be used to modify the FPU
  62          * state in the fpstate buffer:
  63          */
  64         WARN_ON_FPU(fpu == &current->thread.fpu);
  65
  66         __fpu_invalidate_fpregs_state(fpu);
  67 }
  68
  69 int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
  70                 struct membuf to)
  71 {
  72         struct fpu *fpu = &target->thread.fpu;
  73
  74         if (!cpu_feature_enabled(X86_FEATURE_FXSR))
  75                 return -ENODEV;
  76
  77         sync_fpstate(fpu);
  78
  79         if (!use_xsave()) {
  80                 return membuf_write(&to, &fpu->state.fxsave,
  81                                     sizeof(fpu->state.fxsave));
  82         }
  83
  84         copy_xstate_to_uabi_buf(to, target, XSTATE_COPY_FX);
  85         return 0;
  86 }
  87
  88 int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
  89                 unsigned int pos, unsigned int count,
  90                 const void *kbuf, const void __user *ubuf)
  91 {
  92         struct fpu *fpu = &target->thread.fpu;
  93         struct user32_fxsr_struct newstate;
  94         int ret;
  95
  96         BUILD_BUG_ON(sizeof(newstate) != sizeof(struct fxregs_state));
  97
  98         if (!cpu_feature_enabled(X86_FEATURE_FXSR))
  99                 return -ENODEV;
 100
 101         /* No funny business with partial or oversized writes is permitted. */
 102         if (pos != 0 || count != sizeof(newstate))
 103                 return -EINVAL;
 104
 105         ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &newstate, 0, -1);
 106         if (ret)
 107                 return ret;
 108
 109         /* Do not allow an invalid MXCSR value. */
 110         if (newstate.mxcsr & ~mxcsr_feature_mask)
 111                 return -EINVAL;
 112
 113         fpu_force_restore(fpu);
 114
 115         /* Copy the state  */
 116         memcpy(&fpu->state.fxsave, &newstate, sizeof(newstate));
 117
 118         /* Clear xmm8..15 */
 119         BUILD_BUG_ON(sizeof(fpu->state.fxsave.xmm_space) != 16 * 16);
 120         memset(&fpu->state.fxsave.xmm_space[8], 0, 8 * 16);
 121
 122         /* Mark FP and SSE as in use when XSAVE is enabled */
 123         if (use_xsave())
 124                 fpu->state.xsave.header.xfeatures |= XFEATURE_MASK_FPSSE;
 125
 126         return 0;
 127 }
 128
 129 int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
 130                 struct membuf to)
 131 {
 132         if (!cpu_feature_enabled(X86_FEATURE_XSAVE))
 133                 return -ENODEV;
 134
 135         sync_fpstate(&target->thread.fpu);
 136
 137         copy_xstate_to_uabi_buf(to, target, XSTATE_COPY_XSAVE);
 138         return 0;
 139 }
 140
 141 int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
 142                   unsigned int pos, unsigned int count,
 143                   const void *kbuf, const void __user *ubuf)
 144 {
 145         struct fpu *fpu = &target->thread.fpu;
 146         struct xregs_state *tmpbuf = NULL;
 147         int ret;
 148
 149         if (!cpu_feature_enabled(X86_FEATURE_XSAVE))
 150                 return -ENODEV;
 151
 152         /*
 153          * A whole standard-format XSAVE buffer is needed:
 154          */
 155         if (pos != 0 || count != fpu_user_xstate_size)
 156                 return -EFAULT;
 157
 158         if (!kbuf) {
 159                 tmpbuf = vmalloc(count);
 160                 if (!tmpbuf)
 161                         return -ENOMEM;
 162
 163                 if (copy_from_user(tmpbuf, ubuf, count)) {
 164                         ret = -EFAULT;
 165                         goto out;
 166                 }
 167         }
 168
 169         fpu_force_restore(fpu);
 170         ret = copy_uabi_from_kernel_to_xstate(&fpu->state.xsave, kbuf ?: tmpbuf);
 171
 172 out:
 173         vfree(tmpbuf);
 174         return ret;
 175 }
 176
 177 #if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
 178
 179 /*
 180  * FPU tag word conversions.
 181  */
 182
 183 static inline unsigned short twd_i387_to_fxsr(unsigned short twd)
 184 {
 185         unsigned int tmp; /* to avoid 16 bit prefixes in the code */
 186
 187         /* Transform each pair of bits into 01 (valid) or 00 (empty) */
 188         tmp = ~twd;
 189         tmp = (tmp | (tmp>>1)) & 0x5555; /* 0V0V0V0V0V0V0V0V */
 190         /* and move the valid bits to the lower byte. */
 191         tmp = (tmp | (tmp >> 1)) & 0x3333; /* 00VV00VV00VV00VV */
 192         tmp = (tmp | (tmp >> 2)) & 0x0f0f; /* 0000VVVV0000VVVV */
 193         tmp = (tmp | (tmp >> 4)) & 0x00ff; /* 00000000VVVVVVVV */
 194
 195         return tmp;
 196 }
 197
 198 #define FPREG_ADDR(f, n)        ((void *)&(f)->st_space + (n) * 16)
 199 #define FP_EXP_TAG_VALID        0
 200 #define FP_EXP_TAG_ZERO         1
 201 #define FP_EXP_TAG_SPECIAL      2
 202 #define FP_EXP_TAG_EMPTY        3
 203
 204 static inline u32 twd_fxsr_to_i387(struct fxregs_state *fxsave)
 205 {
 206         struct _fpxreg *st;
 207         u32 tos = (fxsave->swd >> 11) & 7;
 208         u32 twd = (unsigned long) fxsave->twd;
 209         u32 tag;
 210         u32 ret = 0xffff0000u;
 211         int i;
 212
 213         for (i = 0; i < 8; i++, twd >>= 1) {
 214                 if (twd & 0x1) {
 215                         st = FPREG_ADDR(fxsave, (i - tos) & 7);
 216
 217                         switch (st->exponent & 0x7fff) {
 218                         case 0x7fff:
 219                                 tag = FP_EXP_TAG_SPECIAL;
 220                                 break;
 221                         case 0x0000:
 222                                 if (!st->significand[0] &&
 223                                     !st->significand[1] &&
 224                                     !st->significand[2] &&
 225                                     !st->significand[3])
 226                                         tag = FP_EXP_TAG_ZERO;
 227                                 else
 228                                         tag = FP_EXP_TAG_SPECIAL;
 229                                 break;
 230                         default:
 231                                 if (st->significand[3] & 0x8000)
 232                                         tag = FP_EXP_TAG_VALID;
 233                                 else
 234                                         tag = FP_EXP_TAG_SPECIAL;
 235                                 break;
 236                         }
 237                 } else {
 238                         tag = FP_EXP_TAG_EMPTY;
 239                 }
 240                 ret |= tag << (2 * i);
 241         }
 242         return ret;
 243 }
 244
 245 /*
 246  * FXSR floating point environment conversions.
 247  */
 248
 249 static void __convert_from_fxsr(struct user_i387_ia32_struct *env,
 250                                 struct task_struct *tsk,
 251                                 struct fxregs_state *fxsave)
 252 {
 253         struct _fpreg *to = (struct _fpreg *) &env->st_space[0];
 254         struct _fpxreg *from = (struct _fpxreg *) &fxsave->st_space[0];
 255         int i;
 256
 257         env->cwd = fxsave->cwd | 0xffff0000u;
 258         env->swd = fxsave->swd | 0xffff0000u;
 259         env->twd = twd_fxsr_to_i387(fxsave);
 260
 261 #ifdef CONFIG_X86_64
 262         env->fip = fxsave->rip;
 263         env->foo = fxsave->rdp;
 264         /*
 265          * should be actually ds/cs at fpu exception time, but
 266          * that information is not available in 64bit mode.
 267          */
 268         env->fcs = task_pt_regs(tsk)->cs;
 269         if (tsk == current) {
 270                 savesegment(ds, env->fos);
 271         } else {
 272                 env->fos = tsk->thread.ds;
 273         }
 274         env->fos |= 0xffff0000;
 275 #else
 276         env->fip = fxsave->fip;
 277         env->fcs = (u16) fxsave->fcs | ((u32) fxsave->fop << 16);
 278         env->foo = fxsave->foo;
 279         env->fos = fxsave->fos;
 280 #endif
 281
 282         for (i = 0; i < 8; ++i)
 283                 memcpy(&to[i], &from[i], sizeof(to[0]));
 284 }
 285
 286 void
 287 convert_from_fxsr(struct user_i387_ia32_struct *env, struct task_struct *tsk)
 288 {
 289         __convert_from_fxsr(env, tsk, &tsk->thread.fpu.state.fxsave);
 290 }
 291
 292 void convert_to_fxsr(struct fxregs_state *fxsave,
 293                      const struct user_i387_ia32_struct *env)
 294
 295 {
 296         struct _fpreg *from = (struct _fpreg *) &env->st_space[0];
 297         struct _fpxreg *to = (struct _fpxreg *) &fxsave->st_space[0];
 298         int i;
 299
 300         fxsave->cwd = env->cwd;
 301         fxsave->swd = env->swd;
 302         fxsave->twd = twd_i387_to_fxsr(env->twd);
 303         fxsave->fop = (u16) ((u32) env->fcs >> 16);
 304 #ifdef CONFIG_X86_64
 305         fxsave->rip = env->fip;
 306         fxsave->rdp = env->foo;
 307         /* cs and ds ignored */
 308 #else
 309         fxsave->fip = env->fip;
 310         fxsave->fcs = (env->fcs & 0xffff);
 311         fxsave->foo = env->foo;
 312         fxsave->fos = env->fos;
 313 #endif
 314
 315         for (i = 0; i < 8; ++i)
 316                 memcpy(&to[i], &from[i], sizeof(from[0]));
 317 }
 318
 319 int fpregs_get(struct task_struct *target, const struct user_regset *regset,
 320                struct membuf to)
 321 {
 322         struct fpu *fpu = &target->thread.fpu;
 323         struct user_i387_ia32_struct env;
 324         struct fxregs_state fxsave, *fx;
 325
 326         sync_fpstate(fpu);
 327
 328         if (!cpu_feature_enabled(X86_FEATURE_FPU))
 329                 return fpregs_soft_get(target, regset, to);
 330
 331         if (!cpu_feature_enabled(X86_FEATURE_FXSR)) {
 332                 return membuf_write(&to, &fpu->state.fsave,
 333                                     sizeof(struct fregs_state));
 334         }
 335
 336         if (use_xsave()) {
 337                 struct membuf mb = { .p = &fxsave, .left = sizeof(fxsave) };
 338
 339                 /* Handle init state optimized xstate correctly */
 340                 copy_xstate_to_uabi_buf(mb, target, XSTATE_COPY_FP);
 341                 fx = &fxsave;
 342         } else {
 343                 fx = &fpu->state.fxsave;
 344         }
 345
 346         __convert_from_fxsr(&env, target, fx);
 347         return membuf_write(&to, &env, sizeof(env));
 348 }
 349
 350 int fpregs_set(struct task_struct *target, const struct user_regset *regset,
 351                unsigned int pos, unsigned int count,
 352                const void *kbuf, const void __user *ubuf)
 353 {
 354         struct fpu *fpu = &target->thread.fpu;
 355         struct user_i387_ia32_struct env;
 356         int ret;
 357
 358         /* No funny business with partial or oversized writes is permitted. */
 359         if (pos != 0 || count != sizeof(struct user_i387_ia32_struct))
 360                 return -EINVAL;
 361
 362         if (!cpu_feature_enabled(X86_FEATURE_FPU))
 363                 return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf);
 364
 365         ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &env, 0, -1);
 366         if (ret)
 367                 return ret;
 368
 369         fpu_force_restore(fpu);
 370
 371         if (cpu_feature_enabled(X86_FEATURE_FXSR))
 372                 convert_to_fxsr(&fpu->state.fxsave, &env);
 373         else
 374                 memcpy(&fpu->state.fsave, &env, sizeof(env));
 375
 376         /*
 377          * Update the header bit in the xsave header, indicating the
 378          * presence of FP.
 379          */
 380         if (cpu_feature_enabled(X86_FEATURE_XSAVE))
 381                 fpu->state.xsave.header.xfeatures |= XFEATURE_MASK_FP;
 382
 383         return 0;
 384 }
 385
 386 #endif  /* CONFIG_X86_32 || CONFIG_IA32_EMULATION */