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         BUILD_BUG_ON(sizeof(struct user_i387_struct) !=
  86                         sizeof(tsk->thread.xstate->fxsave));
  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         clear_used_math(); /* trigger finit */
  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                 __clear_user(buf, sig_xstate_size);
 100
 101                 if (task_thread_info(tsk)->status & TS_XSAVE)
 102                         err = xsave_user(buf);
 103                 else
 104                         err = fxsave_user(buf);
 105
 106                 if (err)
 107                         return err;
 108                 task_thread_info(tsk)->status &= ~TS_USEDFPU;
 109                 stts();
 110         } else {
 111                 if (__copy_to_user(buf, &tsk->thread.xstate->fxsave,
 112                                    xstate_size))
 113                         return -1;
 114         }
 115
 116         if (task_thread_info(tsk)->status & TS_XSAVE) {
 117                 struct _fpstate __user *fx = buf;
 118
 119                 err = __copy_to_user(&fx->sw_reserved, &fx_sw_reserved,
 120                                      sizeof(struct _fpx_sw_bytes));
 121
 122                 err |= __put_user(FP_XSTATE_MAGIC2,
 123                                   (__u32 __user *) (buf + sig_xstate_size
 124                                                     - FP_XSTATE_MAGIC2_SIZE));
 125         }
 126
 127         return 1;
 128 }
 129
 130 /*
 131  * Restore the extended state if present. Otherwise, restore the FP/SSE
 132  * state.
 133  */
 134 int restore_user_xstate(void __user *buf)
 135 {
 136         struct _fpx_sw_bytes fx_sw_user;
 137         u64 mask;
 138         int err;
 139
 140         if (((unsigned long)buf % 64) ||
 141              check_for_xstate(buf, buf, &fx_sw_user))
 142                 goto fx_only;
 143
 144         mask = fx_sw_user.xstate_bv;
 145
 146         /*
 147          * restore the state passed by the user.
 148          */
 149         err = xrestore_user(buf, mask);
 150         if (err)
 151                 return err;
 152
 153         /*
 154          * init the state skipped by the user.
 155          */
 156         mask = pcntxt_mask & ~mask;
 157
 158         xrstor_state(init_xstate_buf, mask);
 159
 160         return 0;
 161
 162 fx_only:
 163         /*
 164          * couldn't find the extended state information in the
 165          * memory layout. Restore just the FP/SSE and init all
 166          * the other extended state.
 167          */
 168         xrstor_state(init_xstate_buf, pcntxt_mask & ~XSTATE_FPSSE);
 169         return fxrstor_checking((__force struct i387_fxsave_struct *)buf);
 170 }
 171
 172 /*
 173  * This restores directly out of user space. Exceptions are handled.
 174  */
 175 int restore_i387_xstate(void __user *buf)
 176 {
 177         struct task_struct *tsk = current;
 178         int err = 0;
 179
 180         if (!buf) {
 181                 if (used_math())
 182                         goto clear;
 183                 return 0;
 184         } else
 185                 if (!access_ok(VERIFY_READ, buf, sig_xstate_size))
 186                         return -EACCES;
 187
 188         if (!used_math()) {
 189                 err = init_fpu(tsk);
 190                 if (err)
 191                         return err;
 192         }
 193
 194         if (!(task_thread_info(current)->status & TS_USEDFPU)) {
 195                 clts();
 196                 task_thread_info(current)->status |= TS_USEDFPU;
 197         }
 198         if (task_thread_info(tsk)->status & TS_XSAVE)
 199                 err = restore_user_xstate(buf);
 200         else
 201                 err = fxrstor_checking((__force struct i387_fxsave_struct *)
 202                                        buf);
 203         if (unlikely(err)) {
 204                 /*
 205                  * Encountered an error while doing the restore from the
 206                  * user buffer, clear the fpu state.
 207                  */
 208 clear:
 209                 clear_fpu(tsk);
 210                 clear_used_math();
 211         }
 212         return err;
 213 }
 214 #endif
 215
 216 /*
 217  * Prepare the SW reserved portion of the fxsave memory layout, indicating
 218  * the presence of the extended state information in the memory layout
 219  * pointed by the fpstate pointer in the sigcontext.
 220  * This will be saved when ever the FP and extended state context is
 221  * saved on the user stack during the signal handler delivery to the user.
 222  */
 223 void prepare_fx_sw_frame(void)
 224 {
 225         int size_extended = (xstate_size - sizeof(struct i387_fxsave_struct)) +
 226                              FP_XSTATE_MAGIC2_SIZE;
 227
 228         sig_xstate_size = sizeof(struct _fpstate) + size_extended;
 229
 230 #ifdef CONFIG_IA32_EMULATION
 231         sig_xstate_ia32_size = sizeof(struct _fpstate_ia32) + size_extended;
 232 #endif
 233
 234         memset(&fx_sw_reserved, 0, sizeof(fx_sw_reserved));
 235
 236         fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
 237         fx_sw_reserved.extended_size = sig_xstate_size;
 238         fx_sw_reserved.xstate_bv = pcntxt_mask;
 239         fx_sw_reserved.xstate_size = xstate_size;
 240 #ifdef CONFIG_IA32_EMULATION
 241         memcpy(&fx_sw_reserved_ia32, &fx_sw_reserved,
 242                sizeof(struct _fpx_sw_bytes));
 243         fx_sw_reserved_ia32.extended_size = sig_xstate_ia32_size;
 244 #endif
 245 }
 246
 247 /*
 248  * Represents init state for the supported extended state.
 249  */
 250 struct xsave_struct *init_xstate_buf;
 251
 252 #ifdef CONFIG_X86_64
 253 unsigned int sig_xstate_size = sizeof(struct _fpstate);
 254 #endif
 255
 256 /*
 257  * Enable the extended processor state save/restore feature
 258  */
 259 void __cpuinit xsave_init(void)
 260 {
 261         if (!cpu_has_xsave)
 262                 return;
 263
 264         set_in_cr4(X86_CR4_OSXSAVE);
 265
 266         /*
 267          * Enable all the features that the HW is capable of
 268          * and the Linux kernel is aware of.
 269          */
 270         xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_mask);
 271 }
 272
 273 /*
 274  * setup the xstate image representing the init state
 275  */
 276 void setup_xstate_init(void)
 277 {
 278         init_xstate_buf = alloc_bootmem(xstate_size);
 279         init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;
 280 }
 281
 282 /*
 283  * Enable and initialize the xsave feature.
 284  */
 285 void __init xsave_cntxt_init(void)
 286 {
 287         unsigned int eax, ebx, ecx, edx;
 288
 289         cpuid_count(0xd, 0, &eax, &ebx, &ecx, &edx);
 290         pcntxt_mask = eax + ((u64)edx << 32);
 291
 292         if ((pcntxt_mask & XSTATE_FPSSE) != XSTATE_FPSSE) {
 293                 printk(KERN_ERR "FP/SSE not shown under xsave features 0x%llx\n",
 294                        pcntxt_mask);
 295                 BUG();
 296         }
 297
 298         /*
 299          * for now OS knows only about FP/SSE
 300          */
 301         pcntxt_mask = pcntxt_mask & XCNTXT_MASK;
 302         xsave_init();
 303
 304         /*
 305          * Recompute the context size for enabled features
 306          */
 307         cpuid_count(0xd, 0, &eax, &ebx, &ecx, &edx);
 308         xstate_size = ebx;
 309
 310         prepare_fx_sw_frame();
 311
 312         setup_xstate_init();
 313
 314         printk(KERN_INFO "xsave/xrstor: enabled xstate_bv 0x%llx, "
 315                "cntxt size 0x%x\n",
 316                pcntxt_mask, xstate_size);
 317 }