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