144 lines
3.2 KiB
C
144 lines
3.2 KiB
C
/*
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* Set up the VMAs to tell the VM about the vDSO.
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* Copyright 2007 Andi Kleen, SUSE Labs.
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* Subject to the GPL, v.2
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*/
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#include <linux/mm.h>
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#include <linux/err.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/init.h>
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#include <linux/random.h>
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#include <linux/elf.h>
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#include <asm/vsyscall.h>
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#include <asm/vgtod.h>
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#include <asm/proto.h>
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#include <asm/vdso.h>
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#include "vextern.h" /* Just for VMAGIC. */
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#undef VEXTERN
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unsigned int __read_mostly vdso_enabled = 1;
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extern char vdso_start[], vdso_end[];
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extern unsigned short vdso_sync_cpuid;
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static struct page **vdso_pages;
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static unsigned vdso_size;
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static inline void *var_ref(void *p, char *name)
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{
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if (*(void **)p != (void *)VMAGIC) {
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printk("VDSO: variable %s broken\n", name);
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vdso_enabled = 0;
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}
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return p;
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}
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static int __init init_vdso_vars(void)
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{
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int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
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int i;
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char *vbase;
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vdso_size = npages << PAGE_SHIFT;
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vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
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if (!vdso_pages)
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goto oom;
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for (i = 0; i < npages; i++) {
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struct page *p;
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p = alloc_page(GFP_KERNEL);
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if (!p)
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goto oom;
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vdso_pages[i] = p;
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copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
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}
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vbase = vmap(vdso_pages, npages, 0, PAGE_KERNEL);
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if (!vbase)
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goto oom;
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if (memcmp(vbase, "\177ELF", 4)) {
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printk("VDSO: I'm broken; not ELF\n");
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vdso_enabled = 0;
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}
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#define VEXTERN(x) \
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*(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #x) = &__ ## x;
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#include "vextern.h"
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#undef VEXTERN
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vunmap(vbase);
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return 0;
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oom:
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printk("Cannot allocate vdso\n");
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vdso_enabled = 0;
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return -ENOMEM;
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}
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subsys_initcall(init_vdso_vars);
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struct linux_binprm;
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/* Put the vdso above the (randomized) stack with another randomized offset.
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This way there is no hole in the middle of address space.
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To save memory make sure it is still in the same PTE as the stack top.
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This doesn't give that many random bits */
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static unsigned long vdso_addr(unsigned long start, unsigned len)
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{
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unsigned long addr, end;
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unsigned offset;
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end = (start + PMD_SIZE - 1) & PMD_MASK;
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if (end >= TASK_SIZE_MAX)
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end = TASK_SIZE_MAX;
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end -= len;
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/* This loses some more bits than a modulo, but is cheaper */
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offset = get_random_int() & (PTRS_PER_PTE - 1);
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addr = start + (offset << PAGE_SHIFT);
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if (addr >= end)
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addr = end;
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return addr;
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}
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/* Setup a VMA at program startup for the vsyscall page.
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Not called for compat tasks */
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int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
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{
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struct mm_struct *mm = current->mm;
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unsigned long addr;
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int ret;
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if (!vdso_enabled)
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return 0;
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down_write(&mm->mmap_sem);
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addr = vdso_addr(mm->start_stack, vdso_size);
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addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0);
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if (IS_ERR_VALUE(addr)) {
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ret = addr;
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goto up_fail;
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}
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current->mm->context.vdso = (void *)addr;
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ret = install_special_mapping(mm, addr, vdso_size,
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VM_READ|VM_EXEC|
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VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
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VM_ALWAYSDUMP,
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vdso_pages);
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if (ret) {
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current->mm->context.vdso = NULL;
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goto up_fail;
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}
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up_fail:
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up_write(&mm->mmap_sem);
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return ret;
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}
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static __init int vdso_setup(char *s)
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{
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vdso_enabled = simple_strtoul(s, NULL, 0);
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return 0;
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}
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__setup("vdso=", vdso_setup);
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