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