arch/i386/kernel/sysenter.c

   1 /*
   2  * linux/arch/i386/kernel/sysenter.c
   3  *
   4  * (C) Copyright 2002 Linus Torvalds
   5  * Portions based on the vdso-randomization code from exec-shield:
   6  * Copyright(C) 2005-2006, Red Hat, Inc., Ingo Molnar
   7  *
   8  * This file contains the needed initializations to support sysenter.
   9  */
  10
  11 #include <linux/init.h>
  12 #include <linux/smp.h>
  13 #include <linux/thread_info.h>
  14 #include <linux/sched.h>
  15 #include <linux/gfp.h>
  16 #include <linux/string.h>
  17 #include <linux/elf.h>
  18 #include <linux/mm.h>
  19 #include <linux/module.h>
  20
  21 #include <asm/cpufeature.h>
  22 #include <asm/msr.h>
  23 #include <asm/pgtable.h>
  24 #include <asm/unistd.h>
  25 #include <asm/elf.h>
  26 #include <asm/tlbflush.h>
  27
  28 enum {
  29         VDSO_DISABLED = 0,
  30         VDSO_ENABLED = 1,
  31         VDSO_COMPAT = 2,
  32 };
  33
  34 #ifdef CONFIG_COMPAT_VDSO
  35 #define VDSO_DEFAULT    VDSO_COMPAT
  36 #else
  37 #define VDSO_DEFAULT    VDSO_ENABLED
  38 #endif
  39
  40 /*
  41  * Should the kernel map a VDSO page into processes and pass its
  42  * address down to glibc upon exec()?
  43  */
  44 unsigned int __read_mostly vdso_enabled = VDSO_DEFAULT;
  45
  46 EXPORT_SYMBOL_GPL(vdso_enabled);
  47
  48 static int __init vdso_setup(char *s)
  49 {
  50         vdso_enabled = simple_strtoul(s, NULL, 0);
  51
  52         return 1;
  53 }
  54
  55 __setup("vdso=", vdso_setup);
  56
  57 extern asmlinkage void sysenter_entry(void);
  58
  59 static __init void reloc_symtab(Elf32_Ehdr *ehdr,
  60                                 unsigned offset, unsigned size)
  61 {
  62         Elf32_Sym *sym = (void *)ehdr + offset;
  63         unsigned nsym = size / sizeof(*sym);
  64         unsigned i;
  65
  66         for(i = 0; i < nsym; i++, sym++) {
  67                 if (sym->st_shndx == SHN_UNDEF ||
  68                     sym->st_shndx == SHN_ABS)
  69                         continue;  /* skip */
  70
  71                 if (sym->st_shndx > SHN_LORESERVE) {
  72                         printk(KERN_INFO "VDSO: unexpected st_shndx %x\n",
  73                                sym->st_shndx);
  74                         continue;
  75                 }
  76
  77                 switch(ELF_ST_TYPE(sym->st_info)) {
  78                 case STT_OBJECT:
  79                 case STT_FUNC:
  80                 case STT_SECTION:
  81                 case STT_FILE:
  82                         sym->st_value += VDSO_HIGH_BASE;
  83                 }
  84         }
  85 }
  86
  87 static __init void reloc_dyn(Elf32_Ehdr *ehdr, unsigned offset)
  88 {
  89         Elf32_Dyn *dyn = (void *)ehdr + offset;
  90
  91         for(; dyn->d_tag != DT_NULL; dyn++)
  92                 switch(dyn->d_tag) {
  93                 case DT_PLTGOT:
  94                 case DT_HASH:
  95                 case DT_STRTAB:
  96                 case DT_SYMTAB:
  97                 case DT_RELA:
  98                 case DT_INIT:
  99                 case DT_FINI:
 100                 case DT_REL:
 101                 case DT_DEBUG:
 102                 case DT_JMPREL:
 103                 case DT_VERSYM:
 104                 case DT_VERDEF:
 105                 case DT_VERNEED:
 106                 case DT_ADDRRNGLO ... DT_ADDRRNGHI:
 107                         /* definitely pointers needing relocation */
 108                         dyn->d_un.d_ptr += VDSO_HIGH_BASE;
 109                         break;
 110
 111                 case DT_ENCODING ... OLD_DT_LOOS-1:
 112                 case DT_LOOS ... DT_HIOS-1:
 113                         /* Tags above DT_ENCODING are pointers if
 114                            they're even */
 115                         if (dyn->d_tag >= DT_ENCODING &&
 116                             (dyn->d_tag & 1) == 0)
 117                                 dyn->d_un.d_ptr += VDSO_HIGH_BASE;
 118                         break;
 119
 120                 case DT_VERDEFNUM:
 121                 case DT_VERNEEDNUM:
 122                 case DT_FLAGS_1:
 123                 case DT_RELACOUNT:
 124                 case DT_RELCOUNT:
 125                 case DT_VALRNGLO ... DT_VALRNGHI:
 126                         /* definitely not pointers */
 127                         break;
 128
 129                 case OLD_DT_LOOS ... DT_LOOS-1:
 130                 case DT_HIOS ... DT_VALRNGLO-1:
 131                 default:
 132                         if (dyn->d_tag > DT_ENCODING)
 133                                 printk(KERN_INFO "VDSO: unexpected DT_tag %x\n",
 134                                        dyn->d_tag);
 135                         break;
 136                 }
 137 }
 138
 139 static __init void relocate_vdso(Elf32_Ehdr *ehdr)
 140 {
 141         Elf32_Phdr *phdr;
 142         Elf32_Shdr *shdr;
 143         int i;
 144
 145         BUG_ON(memcmp(ehdr->e_ident, ELFMAG, 4) != 0 ||
 146                !elf_check_arch(ehdr) ||
 147                ehdr->e_type != ET_DYN);
 148
 149         ehdr->e_entry += VDSO_HIGH_BASE;
 150
 151         /* rebase phdrs */
 152         phdr = (void *)ehdr + ehdr->e_phoff;
 153         for (i = 0; i < ehdr->e_phnum; i++) {
 154                 phdr[i].p_vaddr += VDSO_HIGH_BASE;
 155
 156                 /* relocate dynamic stuff */
 157                 if (phdr[i].p_type == PT_DYNAMIC)
 158                         reloc_dyn(ehdr, phdr[i].p_offset);
 159         }
 160
 161         /* rebase sections */
 162         shdr = (void *)ehdr + ehdr->e_shoff;
 163         for(i = 0; i < ehdr->e_shnum; i++) {
 164                 if (!(shdr[i].sh_flags & SHF_ALLOC))
 165                         continue;
 166
 167                 shdr[i].sh_addr += VDSO_HIGH_BASE;
 168
 169                 if (shdr[i].sh_type == SHT_SYMTAB ||
 170                     shdr[i].sh_type == SHT_DYNSYM)
 171                         reloc_symtab(ehdr, shdr[i].sh_offset,
 172                                      shdr[i].sh_size);
 173         }
 174 }
 175
 176 void enable_sep_cpu(void)
 177 {
 178         int cpu = get_cpu();
 179         struct tss_struct *tss = &per_cpu(init_tss, cpu);
 180
 181         if (!boot_cpu_has(X86_FEATURE_SEP)) {
 182                 put_cpu();
 183                 return;
 184         }
 185
 186         tss->x86_tss.ss1 = __KERNEL_CS;
 187         tss->x86_tss.esp1 = sizeof(struct tss_struct) + (unsigned long) tss;
 188         wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
 189         wrmsr(MSR_IA32_SYSENTER_ESP, tss->x86_tss.esp1, 0);
 190         wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long) sysenter_entry, 0);
 191         put_cpu();
 192 }
 193
 194 static struct vm_area_struct gate_vma;
 195
 196 static int __init gate_vma_init(void)
 197 {
 198         gate_vma.vm_mm = NULL;
 199         gate_vma.vm_start = FIXADDR_USER_START;
 200         gate_vma.vm_end = FIXADDR_USER_END;
 201         gate_vma.vm_flags = VM_READ | VM_MAYREAD | VM_EXEC | VM_MAYEXEC;
 202         gate_vma.vm_page_prot = __P101;
 203         /*
 204          * Make sure the vDSO gets into every core dump.
 205          * Dumping its contents makes post-mortem fully interpretable later
 206          * without matching up the same kernel and hardware config to see
 207          * what PC values meant.
 208          */
 209         gate_vma.vm_flags |= VM_ALWAYSDUMP;
 210         return 0;
 211 }
 212
 213 /*
 214  * These symbols are defined by vsyscall.o to mark the bounds
 215  * of the ELF DSO images included therein.
 216  */
 217 extern const char vsyscall_int80_start, vsyscall_int80_end;
 218 extern const char vsyscall_sysenter_start, vsyscall_sysenter_end;
 219 static struct page *syscall_pages[1];
 220
 221 static void map_compat_vdso(int map)
 222 {
 223         static int vdso_mapped;
 224
 225         if (map == vdso_mapped)
 226                 return;
 227
 228         vdso_mapped = map;
 229
 230         __set_fixmap(FIX_VDSO, page_to_pfn(syscall_pages[0]) << PAGE_SHIFT,
 231                      map ? PAGE_READONLY_EXEC : PAGE_NONE);
 232
 233         /* flush stray tlbs */
 234         flush_tlb_all();
 235 }
 236
 237 int __init sysenter_setup(void)
 238 {
 239         void *syscall_page = (void *)get_zeroed_page(GFP_ATOMIC);
 240         const void *vsyscall;
 241         size_t vsyscall_len;
 242
 243         syscall_pages[0] = virt_to_page(syscall_page);
 244
 245         gate_vma_init();
 246
 247         printk("Compat vDSO mapped to %08lx.\n", __fix_to_virt(FIX_VDSO));
 248
 249         if (!boot_cpu_has(X86_FEATURE_SEP)) {
 250                 vsyscall = &vsyscall_int80_start;
 251                 vsyscall_len = &vsyscall_int80_end - &vsyscall_int80_start;
 252         } else {
 253                 vsyscall = &vsyscall_sysenter_start;
 254                 vsyscall_len = &vsyscall_sysenter_end - &vsyscall_sysenter_start;
 255         }
 256
 257         memcpy(syscall_page, vsyscall, vsyscall_len);
 258         relocate_vdso(syscall_page);
 259
 260         return 0;
 261 }
 262
 263 /* Defined in vsyscall-sysenter.S */
 264 extern void SYSENTER_RETURN;
 265
 266 /* Setup a VMA at program startup for the vsyscall page */
 267 int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)
 268 {
 269         struct mm_struct *mm = current->mm;
 270         unsigned long addr;
 271         int ret = 0;
 272         bool compat;
 273
 274         down_write(&mm->mmap_sem);
 275
 276         /* Test compat mode once here, in case someone
 277            changes it via sysctl */
 278         compat = (vdso_enabled == VDSO_COMPAT);
 279
 280         map_compat_vdso(compat);
 281
 282         if (compat)
 283                 addr = VDSO_HIGH_BASE;
 284         else {
 285                 addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
 286                 if (IS_ERR_VALUE(addr)) {
 287                         ret = addr;
 288                         goto up_fail;
 289                 }
 290
 291                 /*
 292                  * MAYWRITE to allow gdb to COW and set breakpoints
 293                  *
 294                  * Make sure the vDSO gets into every core dump.
 295                  * Dumping its contents makes post-mortem fully
 296                  * interpretable later without matching up the same
 297                  * kernel and hardware config to see what PC values
 298                  * meant.
 299                  */
 300                 ret = install_special_mapping(mm, addr, PAGE_SIZE,
 301                                               VM_READ|VM_EXEC|
 302                                               VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
 303                                               VM_ALWAYSDUMP,
 304                                               syscall_pages);
 305
 306                 if (ret)
 307                         goto up_fail;
 308         }
 309
 310         current->mm->context.vdso = (void *)addr;
 311         current_thread_info()->sysenter_return =
 312                 (void *)VDSO_SYM(&SYSENTER_RETURN);
 313
 314   up_fail:
 315         up_write(&mm->mmap_sem);
 316
 317         return ret;
 318 }
 319
 320 const char *arch_vma_name(struct vm_area_struct *vma)
 321 {
 322         if (vma->vm_mm && vma->vm_start == (long)vma->vm_mm->context.vdso)
 323                 return "[vdso]";
 324         return NULL;
 325 }
 326
 327 struct vm_area_struct *get_gate_vma(struct task_struct *tsk)
 328 {
 329         struct mm_struct *mm = tsk->mm;
 330
 331         /* Check to see if this task was created in compat vdso mode */
 332         if (mm && mm->context.vdso == (void *)VDSO_HIGH_BASE)
 333                 return &gate_vma;
 334         return NULL;
 335 }
 336
 337 int in_gate_area(struct task_struct *task, unsigned long addr)
 338 {
 339         return 0;
 340 }
 341
 342 int in_gate_area_no_task(unsigned long addr)
 343 {
 344         return 0;
 345 }