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