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