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