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