arch/x86/kernel/xsave.c

   1 /*
   2  * xsave/xrstor support.
   3  *
   4  * Author: Suresh Siddha <suresh.b.siddha@intel.com>
   5  */
   6 #include <linux/bootmem.h>
   7 #include <linux/compat.h>
   8 #include <asm/i387.h>
   9 #ifdef CONFIG_IA32_EMULATION
  10 #include <asm/sigcontext32.h>
  11 #endif
  12 #include <asm/xcr.h>
  13
  14 /*
  15  * Supported feature mask by the CPU and the kernel.
  16  */
  17 u64 pcntxt_mask;
  18
  19 struct _fpx_sw_bytes fx_sw_reserved;
  20 #ifdef CONFIG_IA32_EMULATION
  21 struct _fpx_sw_bytes fx_sw_reserved_ia32;
  22 #endif
  23
  24 /*
  25  * Check for the presence of extended state information in the
  26  * user fpstate pointer in the sigcontext.
  27  */
  28 int check_for_xstate(struct i387_fxsave_struct __user *buf,
  29                      void __user *fpstate,
  30                      struct _fpx_sw_bytes *fx_sw_user)
  31 {
  32         int min_xstate_size = sizeof(struct i387_fxsave_struct) +
  33                               sizeof(struct xsave_hdr_struct);
  34         unsigned int magic2;
  35         int err;
  36
  37         err = __copy_from_user(fx_sw_user, &buf->sw_reserved[0],
  38                                sizeof(struct _fpx_sw_bytes));
  39         if (err)
  40                 return -EFAULT;
  41
  42         /*
  43          * First Magic check failed.
  44          */
  45         if (fx_sw_user->magic1 != FP_XSTATE_MAGIC1)
  46                 return -EINVAL;
  47
  48         /*
  49          * Check for error scenarios.
  50          */
  51         if (fx_sw_user->xstate_size < min_xstate_size ||
  52             fx_sw_user->xstate_size > xstate_size ||
  53             fx_sw_user->xstate_size > fx_sw_user->extended_size)
  54                 return -EINVAL;
  55
  56         err = __get_user(magic2, (__u32 *) (((void *)fpstate) +
  57                                             fx_sw_user->extended_size -
  58                                             FP_XSTATE_MAGIC2_SIZE));
  59         if (err)
  60                 return err;
  61         /*
  62          * Check for the presence of second magic word at the end of memory
  63          * layout. This detects the case where the user just copied the legacy
  64          * fpstate layout with out copying the extended state information
  65          * in the memory layout.
  66          */
  67         if (magic2 != FP_XSTATE_MAGIC2)
  68                 return -EFAULT;
  69
  70         return 0;
  71 }
  72
  73 #ifdef CONFIG_X86_64
  74 /*
  75  * Signal frame handlers.
  76  */
  77
  78 int save_i387_xstate(void __user *buf)
  79 {
  80         struct task_struct *tsk = current;
  81         int err = 0;
  82
  83         if (!access_ok(VERIFY_WRITE, buf, sig_xstate_size))
  84                 return -EACCES;
  85
  86         BUG_ON(sig_xstate_size < xstate_size);
  87
  88         if ((unsigned long)buf % 64)
  89                 printk("save_i387_xstate: bad fpstate %p\n", buf);
  90
  91         if (!used_math())
  92                 return 0;
  93
  94         if (task_thread_info(tsk)->status & TS_USEDFPU) {
  95                 /*
  96                  * Start with clearing the user buffer. This will present a
  97                  * clean context for the bytes not touched by the fxsave/xsave.
  98                  */
  99                 err = __clear_user(buf, sig_xstate_size);
 100                 if (err)
 101                         return err;
 102
 103                 if (use_xsave())
 104                         err = xsave_user(buf);
 105                 else
 106                         err = fxsave_user(buf);
 107
 108                 if (err)
 109                         return err;
 110                 task_thread_info(tsk)->status &= ~TS_USEDFPU;
 111                 stts();
 112         } else {
 113                 if (__copy_to_user(buf, &tsk->thread.fpu.state->fxsave,
 114                                    xstate_size))
 115                         return -1;
 116         }
 117
 118         clear_used_math(); /* trigger finit */
 119
 120         if (use_xsave()) {
 121                 struct _fpstate __user *fx = buf;
 122                 struct _xstate __user *x = buf;
 123                 u64 xstate_bv;
 124
 125                 err = __copy_to_user(&fx->sw_reserved, &fx_sw_reserved,
 126                                      sizeof(struct _fpx_sw_bytes));
 127
 128                 err |= __put_user(FP_XSTATE_MAGIC2,
 129                                   (__u32 __user *) (buf + sig_xstate_size
 130                                                     - FP_XSTATE_MAGIC2_SIZE));
 131
 132                 /*
 133                  * Read the xstate_bv which we copied (directly from the cpu or
 134                  * from the state in task struct) to the user buffers and
 135                  * set the FP/SSE bits.
 136                  */
 137                 err |= __get_user(xstate_bv, &x->xstate_hdr.xstate_bv);
 138
 139                 /*
 140                  * For legacy compatible, we always set FP/SSE bits in the bit
 141                  * vector while saving the state to the user context. This will
 142                  * enable us capturing any changes(during sigreturn) to
 143                  * the FP/SSE bits by the legacy applications which don't touch
 144                  * xstate_bv in the xsave header.
 145                  *
 146                  * xsave aware apps can change the xstate_bv in the xsave
 147                  * header as well as change any contents in the memory layout.
 148                  * xrestore as part of sigreturn will capture all the changes.
 149                  */
 150                 xstate_bv |= XSTATE_FPSSE;
 151
 152                 err |= __put_user(xstate_bv, &x->xstate_hdr.xstate_bv);
 153
 154                 if (err)
 155                         return err;
 156         }
 157
 158         return 1;
 159 }
 160
 161 /*
 162  * Restore the extended state if present. Otherwise, restore the FP/SSE
 163  * state.
 164  */
 165 static int restore_user_xstate(void __user *buf)
 166 {
 167         struct _fpx_sw_bytes fx_sw_user;
 168         u64 mask;
 169         int err;
 170
 171         if (((unsigned long)buf % 64) ||
 172              check_for_xstate(buf, buf, &fx_sw_user))
 173                 goto fx_only;
 174
 175         mask = fx_sw_user.xstate_bv;
 176
 177         /*
 178          * restore the state passed by the user.
 179          */
 180         err = xrestore_user(buf, mask);
 181         if (err)
 182                 return err;
 183
 184         /*
 185          * init the state skipped by the user.
 186          */
 187         mask = pcntxt_mask & ~mask;
 188
 189         xrstor_state(init_xstate_buf, mask);
 190
 191         return 0;
 192
 193 fx_only:
 194         /*
 195          * couldn't find the extended state information in the
 196          * memory layout. Restore just the FP/SSE and init all
 197          * the other extended state.
 198          */
 199         xrstor_state(init_xstate_buf, pcntxt_mask & ~XSTATE_FPSSE);
 200         return fxrstor_checking((__force struct i387_fxsave_struct *)buf);
 201 }
 202
 203 /*
 204  * This restores directly out of user space. Exceptions are handled.
 205  */
 206 int restore_i387_xstate(void __user *buf)
 207 {
 208         struct task_struct *tsk = current;
 209         int err = 0;
 210
 211         if (!buf) {
 212                 if (used_math())
 213                         goto clear;
 214                 return 0;
 215         } else
 216                 if (!access_ok(VERIFY_READ, buf, sig_xstate_size))
 217                         return -EACCES;
 218
 219         if (!used_math()) {
 220                 err = init_fpu(tsk);
 221                 if (err)
 222                         return err;
 223         }
 224
 225         if (!(task_thread_info(current)->status & TS_USEDFPU)) {
 226                 clts();
 227                 task_thread_info(current)->status |= TS_USEDFPU;
 228         }
 229         if (use_xsave())
 230                 err = restore_user_xstate(buf);
 231         else
 232                 err = fxrstor_checking((__force struct i387_fxsave_struct *)
 233                                        buf);
 234         if (unlikely(err)) {
 235                 /*
 236                  * Encountered an error while doing the restore from the
 237                  * user buffer, clear the fpu state.
 238                  */
 239 clear:
 240                 clear_fpu(tsk);
 241                 clear_used_math();
 242         }
 243         return err;
 244 }
 245 #endif
 246
 247 /*
 248  * Prepare the SW reserved portion of the fxsave memory layout, indicating
 249  * the presence of the extended state information in the memory layout
 250  * pointed by the fpstate pointer in the sigcontext.
 251  * This will be saved when ever the FP and extended state context is
 252  * saved on the user stack during the signal handler delivery to the user.
 253  */
 254 static void prepare_fx_sw_frame(void)
 255 {
 256         int size_extended = (xstate_size - sizeof(struct i387_fxsave_struct)) +
 257                              FP_XSTATE_MAGIC2_SIZE;
 258
 259         sig_xstate_size = sizeof(struct _fpstate) + size_extended;
 260
 261 #ifdef CONFIG_IA32_EMULATION
 262         sig_xstate_ia32_size = sizeof(struct _fpstate_ia32) + size_extended;
 263 #endif
 264
 265         memset(&fx_sw_reserved, 0, sizeof(fx_sw_reserved));
 266
 267         fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
 268         fx_sw_reserved.extended_size = sig_xstate_size;
 269         fx_sw_reserved.xstate_bv = pcntxt_mask;
 270         fx_sw_reserved.xstate_size = xstate_size;
 271 #ifdef CONFIG_IA32_EMULATION
 272         memcpy(&fx_sw_reserved_ia32, &fx_sw_reserved,
 273                sizeof(struct _fpx_sw_bytes));
 274         fx_sw_reserved_ia32.extended_size = sig_xstate_ia32_size;
 275 #endif
 276 }
 277
 278 /*
 279  * Represents init state for the supported extended state.
 280  */
 281 struct xsave_struct *init_xstate_buf;
 282
 283 #ifdef CONFIG_X86_64
 284 unsigned int sig_xstate_size = sizeof(struct _fpstate);
 285 #endif
 286
 287 /*
 288  * Enable the extended processor state save/restore feature
 289  */
 290 void __cpuinit xsave_init(void)
 291 {
 292         if (!cpu_has_xsave)
 293                 return;
 294
 295         set_in_cr4(X86_CR4_OSXSAVE);
 296
 297         /*
 298          * Enable all the features that the HW is capable of
 299          * and the Linux kernel is aware of.
 300          */
 301         xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_mask);
 302 }
 303
 304 /*
 305  * setup the xstate image representing the init state
 306  */
 307 static void __init setup_xstate_init(void)
 308 {
 309         init_xstate_buf = alloc_bootmem(xstate_size);
 310         init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;
 311 }
 312
 313 /*
 314  * Enable and initialize the xsave feature.
 315  */
 316 void __ref xsave_cntxt_init(void)
 317 {
 318         unsigned int eax, ebx, ecx, edx;
 319
 320         cpuid_count(0xd, 0, &eax, &ebx, &ecx, &edx);
 321         pcntxt_mask = eax + ((u64)edx << 32);
 322
 323         if ((pcntxt_mask & XSTATE_FPSSE) != XSTATE_FPSSE) {
 324                 printk(KERN_ERR "FP/SSE not shown under xsave features 0x%llx\n",
 325                        pcntxt_mask);
 326                 BUG();
 327         }
 328
 329         /*
 330          * Support only the state known to OS.
 331          */
 332         pcntxt_mask = pcntxt_mask & XCNTXT_MASK;
 333         xsave_init();
 334
 335         /*
 336          * Recompute the context size for enabled features
 337          */
 338         cpuid_count(0xd, 0, &eax, &ebx, &ecx, &edx);
 339         xstate_size = ebx;
 340
 341         update_regset_xstate_info(xstate_size, pcntxt_mask);
 342         prepare_fx_sw_frame();
 343
 344         setup_xstate_init();
 345
 346         printk(KERN_INFO "xsave/xrstor: enabled xstate_bv 0x%llx, "
 347                "cntxt size 0x%x\n",
 348                pcntxt_mask, xstate_size);
 349 }