vdso32-setup.c

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/*
 * (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>
#include <asm/vdso.h>
#include <asm/proto.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

#ifdef CONFIG_X86_64
#define vdso_enabled            sysctl_vsyscall32
#define arch_setup_additional_pages syscall32_setup_pages
#endif

/*
 * This is the difference between the prelinked addresses in the vDSO images
 * and the VDSO_HIGH_BASE address where CONFIG_COMPAT_VDSO places the vDSO
 * in the user address space.
 */
#define VDSO_ADDR_ADJUST    (VDSO_HIGH_BASE - (unsigned long)VDSO32_PRELINK)

/*
 * 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;

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

    return 1;
}

/*
 * For consistency, the argument vdso32=[012] affects the 32-bit vDSO
 * behavior on both 64-bit and 32-bit kernels.
 * On 32-bit kernels, vdso=[012] means the same thing.
 */
__setup("vdso32=", vdso_setup);

#ifdef CONFIG_X86_32
__setup_param("vdso=", vdso32_setup, vdso_setup, 0);

EXPORT_SYMBOL_GPL(vdso_enabled);
#endif

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_ADDR_ADJUST;
        }
    }
}

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_ADDR_ADJUST;
            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_ADDR_ADJUST;
            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, SELFMAG) != 0 ||
           !elf_check_arch_ia32(ehdr) ||
           ehdr->e_type != ET_DYN);

    ehdr->e_entry += VDSO_ADDR_ADJUST;

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

        /* 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_ADDR_ADJUST;

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

static struct page *vdso32_pages[1];

#ifdef CONFIG_X86_64

#define vdso32_sysenter()   (boot_cpu_has(X86_FEATURE_SYSENTER32))
#define vdso32_syscall()    (boot_cpu_has(X86_FEATURE_SYSCALL32))

/* May not be __init: called during resume */
void syscall32_cpu_init(void)
{
    /* Load these always in case some future AMD CPU supports
       SYSENTER from compat mode too. */
    wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)__KERNEL_CS);
    wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
    wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)ia32_sysenter_target);

    wrmsrl(MSR_CSTAR, ia32_cstar_target);
}

#define compat_uses_vma     1

static inline void map_compat_vdso(int map)
{
}

#else  /* CONFIG_X86_32 */

#define vdso32_sysenter()   (boot_cpu_has(X86_FEATURE_SEP))
#define vdso32_syscall()    (0)

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.sp1 = sizeof(struct tss_struct) + (unsigned long) tss;
    wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
    wrmsr(MSR_IA32_SYSENTER_ESP, tss->x86_tss.sp1, 0);
    wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long) ia32_sysenter_target, 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;

    return 0;
}

#define compat_uses_vma     0

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(vdso32_pages[0]) << PAGE_SHIFT,
             map ? PAGE_READONLY_EXEC : PAGE_NONE);

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

#endif  /* CONFIG_X86_64 */

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

    vdso32_pages[0] = virt_to_page(syscall_page);

#ifdef CONFIG_X86_32
    gate_vma_init();
#endif

    if (vdso32_syscall()) {
        vsyscall = &vdso32_syscall_start;
        vsyscall_len = &vdso32_syscall_end - &vdso32_syscall_start;
    } else if (vdso32_sysenter()){
        vsyscall = &vdso32_sysenter_start;
        vsyscall_len = &vdso32_sysenter_end - &vdso32_sysenter_start;
    } else {
        vsyscall = &vdso32_int80_start;
        vsyscall_len = &vdso32_int80_end - &vdso32_int80_start;
    }

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

    return 0;
}

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

#ifdef CONFIG_X86_X32_ABI
    if (test_thread_flag(TIF_X32))
        return x32_setup_additional_pages(bprm, uses_interp);
#endif

    if (vdso_enabled == VDSO_DISABLED)
        return 0;

    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;
        }
    }

    current->mm->context.vdso = (void *)addr;

    if (compat_uses_vma || !compat) {
        /*
         * MAYWRITE to allow gdb to COW and set breakpoints
         */
        ret = install_special_mapping(mm, addr, PAGE_SIZE,
                          VM_READ|VM_EXEC|
                          VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
                          vdso32_pages);

        if (ret)
            goto up_fail;
    }

    current_thread_info()->sysenter_return =
        VDSO32_SYMBOL(addr, SYSENTER_RETURN);

  up_fail:
    if (ret)
        current->mm->context.vdso = NULL;

    up_write(&mm->mmap_sem);

    return ret;
}

#ifdef CONFIG_X86_64

subsys_initcall(sysenter_setup);

#ifdef CONFIG_SYSCTL
/* Register vsyscall32 into the ABI table */
#include <linux/sysctl.h>

static ctl_table abi_table2[] = {
    {
        .procname   = "vsyscall32",
        .data       = &sysctl_vsyscall32,
        .maxlen     = sizeof(int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec
    },
    {}
};

static ctl_table abi_root_table2[] = {
    {
        .procname = "abi",
        .mode = 0555,
        .child = abi_table2
    },
    {}
};

static __init int ia32_binfmt_init(void)
{
    register_sysctl_table(abi_root_table2);
    return 0;
}
__initcall(ia32_binfmt_init);
#endif

#else  /* CONFIG_X86_32 */

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 mm_struct *mm)
{
    /*
     * Check to see if the corresponding 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 mm_struct *mm, unsigned long addr)
{
    const struct vm_area_struct *vma = get_gate_vma(mm);

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

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

#endif  /* CONFIG_X86_64 */