/* * linux/arch/i386/mm/fault.c * * Copyright (C) 1995 Linus Torvalds */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* For unblank_screen() */ #include #include /* for max_low_pfn */ #include #include #include #include #include #include #include #include #include extern void die(const char *,struct pt_regs *,long); #ifdef CONFIG_KPROBES static inline int notify_page_fault(struct pt_regs *regs) { int ret = 0; /* kprobe_running() needs smp_processor_id() */ if (!user_mode_vm(regs)) { preempt_disable(); if (kprobe_running() && kprobe_fault_handler(regs, 14)) ret = 1; preempt_enable(); } return ret; } #else static inline int notify_page_fault(struct pt_regs *regs) { return 0; } #endif /* * Return EIP plus the CS segment base. The segment limit is also * adjusted, clamped to the kernel/user address space (whichever is * appropriate), and returned in *eip_limit. * * The segment is checked, because it might have been changed by another * task between the original faulting instruction and here. * * If CS is no longer a valid code segment, or if EIP is beyond the * limit, or if it is a kernel address when CS is not a kernel segment, * then the returned value will be greater than *eip_limit. * * This is slow, but is very rarely executed. */ static inline unsigned long get_segment_eip(struct pt_regs *regs, unsigned long *eip_limit) { unsigned long eip = regs->eip; unsigned seg = regs->xcs & 0xffff; u32 seg_ar, seg_limit, base, *desc; /* Unlikely, but must come before segment checks. */ if (unlikely(regs->eflags & VM_MASK)) { base = seg << 4; *eip_limit = base + 0xffff; return base + (eip & 0xffff); } /* The standard kernel/user address space limit. */ *eip_limit = user_mode(regs) ? USER_DS.seg : KERNEL_DS.seg; /* By far the most common cases. */ if (likely(SEGMENT_IS_FLAT_CODE(seg))) return eip; /* Check the segment exists, is within the current LDT/GDT size, that kernel/user (ring 0..3) has the appropriate privilege, that it's a code segment, and get the limit. */ __asm__ ("larl %3,%0; lsll %3,%1" : "=&r" (seg_ar), "=r" (seg_limit) : "0" (0), "rm" (seg)); if ((~seg_ar & 0x9800) || eip > seg_limit) { *eip_limit = 0; return 1; /* So that returned eip > *eip_limit. */ } /* Get the GDT/LDT descriptor base. When you look for races in this code remember that LDT and other horrors are only used in user space. */ if (seg & (1<<2)) { /* Must lock the LDT while reading it. */ mutex_lock(¤t->mm->context.lock); desc = current->mm->context.ldt; desc = (void *)desc + (seg & ~7); } else { /* Must disable preemption while reading the GDT. */ desc = (u32 *)get_cpu_gdt_table(get_cpu()); desc = (void *)desc + (seg & ~7); } /* Decode the code segment base from the descriptor */ base = get_desc_base((unsigned long *)desc); if (seg & (1<<2)) { mutex_unlock(¤t->mm->context.lock); } else put_cpu(); /* Adjust EIP and segment limit, and clamp at the kernel limit. It's legitimate for segments to wrap at 0xffffffff. */ seg_limit += base; if (seg_limit < *eip_limit && seg_limit >= base) *eip_limit = seg_limit; return eip + base; } /* * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. * Check that here and ignore it. */ static int __is_prefetch(struct pt_regs *regs, unsigned long addr) { unsigned long limit; unsigned char *instr = (unsigned char *)get_segment_eip (regs, &limit); int scan_more = 1; int prefetch = 0; int i; for (i = 0; scan_more && i < 15; i++) { unsigned char opcode; unsigned char instr_hi; unsigned char instr_lo; if (instr > (unsigned char *)limit) break; if (probe_kernel_address(instr, opcode)) break; instr_hi = opcode & 0xf0; instr_lo = opcode & 0x0f; instr++; switch (instr_hi) { case 0x20: case 0x30: /* Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. */ scan_more = ((instr_lo & 7) == 0x6); break; case 0x60: /* 0x64 thru 0x67 are valid prefixes in all modes. */ scan_more = (instr_lo & 0xC) == 0x4; break; case 0xF0: /* 0xF0, 0xF2, and 0xF3 are valid prefixes */ scan_more = !instr_lo || (instr_lo>>1) == 1; break; case 0x00: /* Prefetch instruction is 0x0F0D or 0x0F18 */ scan_more = 0; if (instr > (unsigned char *)limit) break; if (probe_kernel_address(instr, opcode)) break; prefetch = (instr_lo == 0xF) && (opcode == 0x0D || opcode == 0x18); break; default: scan_more = 0; break; } } return prefetch; } static inline int is_prefetch(struct pt_regs *regs, unsigned long addr, unsigned long error_code) { if (unlikely(boot_cpu_data.x86_vendor == X86_VENDOR_AMD && boot_cpu_data.x86 >= 6)) { /* Catch an obscure case of prefetch inside an NX page. */ if (nx_enabled && (error_code & 16)) return 0; return __is_prefetch(regs, addr); } return 0; } static noinline void force_sig_info_fault(int si_signo, int si_code, unsigned long address, struct task_struct *tsk) { siginfo_t info; info.si_signo = si_signo; info.si_errno = 0; info.si_code = si_code; info.si_addr = (void __user *)address; force_sig_info(si_signo, &info, tsk); } fastcall void do_invalid_op(struct pt_regs *, unsigned long); static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address) { unsigned index = pgd_index(address); pgd_t *pgd_k; pud_t *pud, *pud_k; pmd_t *pmd, *pmd_k; pgd += index; pgd_k = init_mm.pgd + index; if (!pgd_present(*pgd_k)) return NULL; /* * set_pgd(pgd, *pgd_k); here would be useless on PAE * and redundant with the set_pmd() on non-PAE. As would * set_pud. */ pud = pud_offset(pgd, address); pud_k = pud_offset(pgd_k, address); if (!pud_present(*pud_k)) return NULL; pmd = pmd_offset(pud, address); pmd_k = pmd_offset(pud_k, address); if (!pmd_present(*pmd_k)) return NULL; if (!pmd_present(*pmd)) { set_pmd(pmd, *pmd_k); arch_flush_lazy_mmu_mode(); } else BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k)); return pmd_k; } /* * Handle a fault on the vmalloc or module mapping area * * This assumes no large pages in there. */ static inline int vmalloc_fault(unsigned long address) { unsigned long pgd_paddr; pmd_t *pmd_k; pte_t *pte_k; /* * Synchronize this task's top level page-table * with the 'reference' page table. * * Do _not_ use "current" here. We might be inside * an interrupt in the middle of a task switch.. */ pgd_paddr = read_cr3(); pmd_k = vmalloc_sync_one(__va(pgd_paddr), address); if (!pmd_k) return -1; pte_k = pte_offset_kernel(pmd_k, address); if (!pte_present(*pte_k)) return -1; return 0; } int show_unhandled_signals = 1; /* * This routine handles page faults. It determines the address, * and the problem, and then passes it off to one of the appropriate * routines. * * error_code: * bit 0 == 0 means no page found, 1 means protection fault * bit 1 == 0 means read, 1 means write * bit 2 == 0 means kernel, 1 means user-mode * bit 3 == 1 means use of reserved bit detected * bit 4 == 1 means fault was an instruction fetch */ fastcall void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code) { struct task_struct *tsk; struct mm_struct *mm; struct vm_area_struct * vma; unsigned long address; int write, si_code; int fault; /* get the address */ address = read_cr2(); tsk = current; si_code = SEGV_MAPERR; /* * We fault-in kernel-space virtual memory on-demand. The * 'reference' page table is init_mm.pgd. * * NOTE! We MUST NOT take any locks for this case. We may * be in an interrupt or a critical region, and should * only copy the information from the master page table, * nothing more. * * This verifies that the fault happens in kernel space * (error_code & 4) == 0, and that the fault was not a * protection error (error_code & 9) == 0. */ if (unlikely(address >= TASK_SIZE)) { if (!(error_code & 0x0000000d) && vmalloc_fault(address) >= 0) return; if (notify_page_fault(regs)) return; /* * Don't take the mm semaphore here. If we fixup a prefetch * fault we could otherwise deadlock. */ goto bad_area_nosemaphore; } if (notify_page_fault(regs)) return; /* It's safe to allow irq's after cr2 has been saved and the vmalloc fault has been handled. */ if (regs->eflags & (X86_EFLAGS_IF|VM_MASK)) local_irq_enable(); mm = tsk->mm; /* * If we're in an interrupt, have no user context or are running in an * atomic region then we must not take the fault.. */ if (in_atomic() || !mm) goto bad_area_nosemaphore; /* When running in the kernel we expect faults to occur only to * addresses in user space. All other faults represent errors in the * kernel and should generate an OOPS. Unfortunately, in the case of an * erroneous fault occurring in a code path which already holds mmap_sem * we will deadlock attempting to validate the fault against the * address space. Luckily the kernel only validly references user * space from well defined areas of code, which are listed in the * exceptions table. * * As the vast majority of faults will be valid we will only perform * the source reference check when there is a possibility of a deadlock. * Attempt to lock the address space, if we cannot we then validate the * source. If this is invalid we can skip the address space check, * thus avoiding the deadlock. */ if (!down_read_trylock(&mm->mmap_sem)) { if ((error_code & 4) == 0 && !search_exception_tables(regs->eip)) goto bad_area_nosemaphore; down_read(&mm->mmap_sem); } vma = find_vma(mm, address); if (!vma) goto bad_area; if (vma->vm_start <= address) goto good_area; if (!(vma->vm_flags & VM_GROWSDOWN)) goto bad_area; if (error_code & 4) { /* * Accessing the stack below %esp is always a bug. * The large cushion allows instructions like enter * and pusha to work. ("enter $65535,$31" pushes * 32 pointers and then decrements %esp by 65535.) */ if (address + 65536 + 32 * sizeof(unsigned long) < regs->esp) goto bad_area; } if (expand_stack(vma, address)) goto bad_area; /* * Ok, we have a good vm_area for this memory access, so * we can handle it.. */ good_area: si_code = SEGV_ACCERR; write = 0; switch (error_code & 3) { default: /* 3: write, present */ /* fall through */ case 2: /* write, not present */ if (!(vma->vm_flags & VM_WRITE)) goto bad_area; write++; break; case 1: /* read, present */ goto bad_area; case 0: /* read, not present */ if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))) goto bad_area; } survive: /* * If for any reason at all we couldn't handle the fault, * make sure we exit gracefully rather than endlessly redo * the fault. */ fault = handle_mm_fault(mm, vma, address, write); if (unlikely(fault & VM_FAULT_ERROR)) { if (fault & VM_FAULT_OOM) goto out_of_memory; else if (fault & VM_FAULT_SIGBUS) goto do_sigbus; BUG(); } if (fault & VM_FAULT_MAJOR) tsk->maj_flt++; else tsk->min_flt++; /* * Did it hit the DOS screen memory VA from vm86 mode? */ if (regs->eflags & VM_MASK) { unsigned long bit = (address - 0xA0000) >> PAGE_SHIFT; if (bit < 32) tsk->thread.screen_bitmap |= 1 << bit; } up_read(&mm->mmap_sem); return; /* * Something tried to access memory that isn't in our memory map.. * Fix it, but check if it's kernel or user first.. */ bad_area: up_read(&mm->mmap_sem); bad_area_nosemaphore: /* User mode accesses just cause a SIGSEGV */ if (error_code & 4) { /* * It's possible to have interrupts off here. */ local_irq_enable(); /* * Valid to do another page fault here because this one came * from user space. */ if (is_prefetch(regs, address, error_code)) return; if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) && printk_ratelimit()) { printk("%s%s[%d]: segfault at %08lx eip %08lx " "esp %08lx error %lx\n", task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG, tsk->comm, task_pid_nr(tsk), address, regs->eip, regs->esp, error_code); } tsk->thread.cr2 = address; /* Kernel addresses are always protection faults */ tsk->thread.error_code = error_code | (address >= TASK_SIZE); tsk->thread.trap_no = 14; force_sig_info_fault(SIGSEGV, si_code, address, tsk); return; } #ifdef CONFIG_X86_F00F_BUG /* * Pentium F0 0F C7 C8 bug workaround. */ if (boot_cpu_data.f00f_bug) { unsigned long nr; nr = (address - idt_descr.address) >> 3; if (nr == 6) { do_invalid_op(regs, 0); return; } } #endif no_context: /* Are we prepared to handle this kernel fault? */ if (fixup_exception(regs)) return; /* * Valid to do another page fault here, because if this fault * had been triggered by is_prefetch fixup_exception would have * handled it. */ if (is_prefetch(regs, address, error_code)) return; /* * Oops. The kernel tried to access some bad page. We'll have to * terminate things with extreme prejudice. */ bust_spinlocks(1); if (oops_may_print()) { __typeof__(pte_val(__pte(0))) page; #ifdef CONFIG_X86_PAE if (error_code & 16) { pte_t *pte = lookup_address(address); if (pte && pte_present(*pte) && !pte_exec_kernel(*pte)) printk(KERN_CRIT "kernel tried to execute " "NX-protected page - exploit attempt? " "(uid: %d)\n", current->uid); } #endif if (address < PAGE_SIZE) printk(KERN_ALERT "BUG: unable to handle kernel NULL " "pointer dereference"); else printk(KERN_ALERT "BUG: unable to handle kernel paging" " request"); printk(" at virtual address %08lx\n",address); printk(KERN_ALERT "printing eip: %08lx ", regs->eip); page = read_cr3(); page = ((__typeof__(page) *) __va(page))[address >> PGDIR_SHIFT]; #ifdef CONFIG_X86_PAE printk("*pdpt = %016Lx ", page); if ((page >> PAGE_SHIFT) < max_low_pfn && page & _PAGE_PRESENT) { page &= PAGE_MASK; page = ((__typeof__(page) *) __va(page))[(address >> PMD_SHIFT) & (PTRS_PER_PMD - 1)]; printk(KERN_ALERT "*pde = %016Lx ", page); page &= ~_PAGE_NX; } #else printk("*pde = %08lx ", page); #endif /* * We must not directly access the pte in the highpte * case if the page table is located in highmem. * And let's rather not kmap-atomic the pte, just in case * it's allocated already. */ if ((page >> PAGE_SHIFT) < max_low_pfn && (page & _PAGE_PRESENT)) { page &= PAGE_MASK; page = ((__typeof__(page) *) __va(page))[(address >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)]; printk("*pte = %0*Lx ", sizeof(page)*2, (u64)page); } printk("\n"); } tsk->thread.cr2 = address; tsk->thread.trap_no = 14; tsk->thread.error_code = error_code; die("Oops", regs, error_code); bust_spinlocks(0); do_exit(SIGKILL); /* * We ran out of memory, or some other thing happened to us that made * us unable to handle the page fault gracefully. */ out_of_memory: up_read(&mm->mmap_sem); if (is_global_init(tsk)) { yield(); down_read(&mm->mmap_sem); goto survive; } printk("VM: killing process %s\n", tsk->comm); if (error_code & 4) do_group_exit(SIGKILL); goto no_context; do_sigbus: up_read(&mm->mmap_sem); /* Kernel mode? Handle exceptions or die */ if (!(error_code & 4)) goto no_context; /* User space => ok to do another page fault */ if (is_prefetch(regs, address, error_code)) return; tsk->thread.cr2 = address; tsk->thread.error_code = error_code; tsk->thread.trap_no = 14; force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk); } void vmalloc_sync_all(void) { /* * Note that races in the updates of insync and start aren't * problematic: insync can only get set bits added, and updates to * start are only improving performance (without affecting correctness * if undone). */ static DECLARE_BITMAP(insync, PTRS_PER_PGD); static unsigned long start = TASK_SIZE; unsigned long address; if (SHARED_KERNEL_PMD) return; BUILD_BUG_ON(TASK_SIZE & ~PGDIR_MASK); for (address = start; address >= TASK_SIZE; address += PGDIR_SIZE) { if (!test_bit(pgd_index(address), insync)) { unsigned long flags; struct page *page; spin_lock_irqsave(&pgd_lock, flags); for (page = pgd_list; page; page = (struct page *)page->index) if (!vmalloc_sync_one(page_address(page), address)) { BUG_ON(page != pgd_list); break; } spin_unlock_irqrestore(&pgd_lock, flags); if (!page) set_bit(pgd_index(address), insync); } if (address == start && test_bit(pgd_index(address), insync)) start = address + PGDIR_SIZE; } }