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sysenter_32.c

/*
 * (C) Copyright 2002 Linus Torvalds
 * Portions based on the vdso-randomization code from exec-shield:
 * Copyright(C) 2005-2006, Red Hat, Inc., Ingo Molnar
 *
 * This file contains the needed initializations to support sysenter.
 */

#include <linux/init.h>
#include <linux/smp.h>
#include <linux/thread_info.h>
#include <linux/sched.h>
#include <linux/gfp.h>
#include <linux/string.h>
#include <linux/elf.h>
#include <linux/mm.h>
#include <linux/err.h>
#include <linux/module.h>

#include <asm/cpufeature.h>
#include <asm/msr.h>
#include <asm/pgtable.h>
#include <asm/unistd.h>
#include <asm/elf.h>
#include <asm/tlbflush.h>

enum {
      VDSO_DISABLED = 0,
      VDSO_ENABLED = 1,
      VDSO_COMPAT = 2,
};

#ifdef CONFIG_COMPAT_VDSO
#define VDSO_DEFAULT    VDSO_COMPAT
#else
#define VDSO_DEFAULT    VDSO_ENABLED
#endif

/*
 * Should the kernel map a VDSO page into processes and pass its
 * address down to glibc upon exec()?
 */
unsigned int __read_mostly vdso_enabled = VDSO_DEFAULT;

EXPORT_SYMBOL_GPL(vdso_enabled);

static int __init vdso_setup(char *s)
{
      vdso_enabled = simple_strtoul(s, NULL, 0);

      return 1;
}

__setup("vdso=", vdso_setup);

extern asmlinkage void sysenter_entry(void);

static __init void reloc_symtab(Elf32_Ehdr *ehdr,
                        unsigned offset, unsigned size)
{
      Elf32_Sym *sym = (void *)ehdr + offset;
      unsigned nsym = size / sizeof(*sym);
      unsigned i;

      for(i = 0; i < nsym; i++, sym++) {
            if (sym->st_shndx == SHN_UNDEF ||
                sym->st_shndx == SHN_ABS)
                  continue;  /* skip */

            if (sym->st_shndx > SHN_LORESERVE) {
                  printk(KERN_INFO "VDSO: unexpected st_shndx %x\n",
                         sym->st_shndx);
                  continue;
            }

            switch(ELF_ST_TYPE(sym->st_info)) {
            case STT_OBJECT:
            case STT_FUNC:
            case STT_SECTION:
            case STT_FILE:
                  sym->st_value += VDSO_HIGH_BASE;
            }
      }
}

static __init void reloc_dyn(Elf32_Ehdr *ehdr, unsigned offset)
{
      Elf32_Dyn *dyn = (void *)ehdr + offset;

      for(; dyn->d_tag != DT_NULL; dyn++)
            switch(dyn->d_tag) {
            case DT_PLTGOT:
            case DT_HASH:
            case DT_STRTAB:
            case DT_SYMTAB:
            case DT_RELA:
            case DT_INIT:
            case DT_FINI:
            case DT_REL:
            case DT_DEBUG:
            case DT_JMPREL:
            case DT_VERSYM:
            case DT_VERDEF:
            case DT_VERNEED:
            case DT_ADDRRNGLO ... DT_ADDRRNGHI:
                  /* definitely pointers needing relocation */
                  dyn->d_un.d_ptr += VDSO_HIGH_BASE;
                  break;

            case DT_ENCODING ... OLD_DT_LOOS-1:
            case DT_LOOS ... DT_HIOS-1:
                  /* Tags above DT_ENCODING are pointers if
                     they're even */
                  if (dyn->d_tag >= DT_ENCODING &&
                      (dyn->d_tag & 1) == 0)
                        dyn->d_un.d_ptr += VDSO_HIGH_BASE;
                  break;

            case DT_VERDEFNUM:
            case DT_VERNEEDNUM:
            case DT_FLAGS_1:
            case DT_RELACOUNT:
            case DT_RELCOUNT:
            case DT_VALRNGLO ... DT_VALRNGHI:
                  /* definitely not pointers */
                  break;

            case OLD_DT_LOOS ... DT_LOOS-1:
            case DT_HIOS ... DT_VALRNGLO-1:
            default:
                  if (dyn->d_tag > DT_ENCODING)
                        printk(KERN_INFO "VDSO: unexpected DT_tag %x\n",
                               dyn->d_tag);
                  break;
            }
}

static __init void relocate_vdso(Elf32_Ehdr *ehdr)
{
      Elf32_Phdr *phdr;
      Elf32_Shdr *shdr;
      int i;

      BUG_ON(memcmp(ehdr->e_ident, ELFMAG, 4) != 0 ||
             !elf_check_arch(ehdr) ||
             ehdr->e_type != ET_DYN);

      ehdr->e_entry += VDSO_HIGH_BASE;

      /* rebase phdrs */
      phdr = (void *)ehdr + ehdr->e_phoff;
      for (i = 0; i < ehdr->e_phnum; i++) {
            phdr[i].p_vaddr += VDSO_HIGH_BASE;

            /* relocate dynamic stuff */
            if (phdr[i].p_type == PT_DYNAMIC)
                  reloc_dyn(ehdr, phdr[i].p_offset);
      }

      /* rebase sections */
      shdr = (void *)ehdr + ehdr->e_shoff;
      for(i = 0; i < ehdr->e_shnum; i++) {
            if (!(shdr[i].sh_flags & SHF_ALLOC))
                  continue;

            shdr[i].sh_addr += VDSO_HIGH_BASE;

            if (shdr[i].sh_type == SHT_SYMTAB ||
                shdr[i].sh_type == SHT_DYNSYM)
                  reloc_symtab(ehdr, shdr[i].sh_offset,
                             shdr[i].sh_size);
      }
}

void enable_sep_cpu(void)
{
      int cpu = get_cpu();
      struct tss_struct *tss = &per_cpu(init_tss, cpu);

      if (!boot_cpu_has(X86_FEATURE_SEP)) {
            put_cpu();
            return;
      }

      tss->x86_tss.ss1 = __KERNEL_CS;
      tss->x86_tss.esp1 = sizeof(struct tss_struct) + (unsigned long) tss;
      wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
      wrmsr(MSR_IA32_SYSENTER_ESP, tss->x86_tss.esp1, 0);
      wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long) sysenter_entry, 0);
      put_cpu();  
}

static struct vm_area_struct gate_vma;

static int __init gate_vma_init(void)
{
      gate_vma.vm_mm = NULL;
      gate_vma.vm_start = FIXADDR_USER_START;
      gate_vma.vm_end = FIXADDR_USER_END;
      gate_vma.vm_flags = VM_READ | VM_MAYREAD | VM_EXEC | VM_MAYEXEC;
      gate_vma.vm_page_prot = __P101;
      /*
       * Make sure the vDSO gets into every core dump.
       * Dumping its contents makes post-mortem fully interpretable later
       * without matching up the same kernel and hardware config to see
       * what PC values meant.
       */
      gate_vma.vm_flags |= VM_ALWAYSDUMP;
      return 0;
}

/*
 * These symbols are defined by vsyscall.o to mark the bounds
 * of the ELF DSO images included therein.
 */
extern const char vsyscall_int80_start, vsyscall_int80_end;
extern const char vsyscall_sysenter_start, vsyscall_sysenter_end;
static struct page *syscall_pages[1];

static void map_compat_vdso(int map)
{
      static int vdso_mapped;

      if (map == vdso_mapped)
            return;

      vdso_mapped = map;

      __set_fixmap(FIX_VDSO, page_to_pfn(syscall_pages[0]) << PAGE_SHIFT,
                 map ? PAGE_READONLY_EXEC : PAGE_NONE);

      /* flush stray tlbs */
      flush_tlb_all();
}

int __init sysenter_setup(void)
{
      void *syscall_page = (void *)get_zeroed_page(GFP_ATOMIC);
      const void *vsyscall;
      size_t vsyscall_len;

      syscall_pages[0] = virt_to_page(syscall_page);

      gate_vma_init();

      printk("Compat vDSO mapped to %08lx.\n", __fix_to_virt(FIX_VDSO));

      if (!boot_cpu_has(X86_FEATURE_SEP)) {
            vsyscall = &vsyscall_int80_start;
            vsyscall_len = &vsyscall_int80_end - &vsyscall_int80_start;
      } else {
            vsyscall = &vsyscall_sysenter_start;
            vsyscall_len = &vsyscall_sysenter_end - &vsyscall_sysenter_start;
      }

      memcpy(syscall_page, vsyscall, vsyscall_len);
      relocate_vdso(syscall_page);

      return 0;
}

/* Defined in vsyscall-sysenter.S */
extern void SYSENTER_RETURN;

/* Setup a VMA at program startup for the vsyscall page */
int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)
{
      struct mm_struct *mm = current->mm;
      unsigned long addr;
      int ret = 0;
      bool compat;

      down_write(&mm->mmap_sem);

      /* Test compat mode once here, in case someone
         changes it via sysctl */
      compat = (vdso_enabled == VDSO_COMPAT);

      map_compat_vdso(compat);

      if (compat)
            addr = VDSO_HIGH_BASE;
      else {
            addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
            if (IS_ERR_VALUE(addr)) {
                  ret = addr;
                  goto up_fail;
            }

            /*
             * MAYWRITE to allow gdb to COW and set breakpoints
             *
             * Make sure the vDSO gets into every core dump.
             * Dumping its contents makes post-mortem fully
             * interpretable later without matching up the same
             * kernel and hardware config to see what PC values
             * meant.
             */
            ret = install_special_mapping(mm, addr, PAGE_SIZE,
                                    VM_READ|VM_EXEC|
                                    VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
                                    VM_ALWAYSDUMP,
                                    syscall_pages);

            if (ret)
                  goto up_fail;
      }

      current->mm->context.vdso = (void *)addr;
      current_thread_info()->sysenter_return =
            (void *)VDSO_SYM(&SYSENTER_RETURN);

  up_fail:
      up_write(&mm->mmap_sem);

      return ret;
}

const char *arch_vma_name(struct vm_area_struct *vma)
{
      if (vma->vm_mm && vma->vm_start == (long)vma->vm_mm->context.vdso)
            return "[vdso]";
      return NULL;
}

struct vm_area_struct *get_gate_vma(struct task_struct *tsk)
{
      struct mm_struct *mm = tsk->mm;

      /* Check to see if this task was created in compat vdso mode */
      if (mm && mm->context.vdso == (void *)VDSO_HIGH_BASE)
            return &gate_vma;
      return NULL;
}

int in_gate_area(struct task_struct *task, unsigned long addr)
{
      const struct vm_area_struct *vma = get_gate_vma(task);

      return vma && addr >= vma->vm_start && addr < vma->vm_end;
}

int in_gate_area_no_task(unsigned long addr)
{
      return 0;
}

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