/* * Copyright (C) 1995 Linus Torvalds * Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs. * Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* * Page fault error code bits: * * bit 0 == 0: no page found 1: protection fault * bit 1 == 0: read access 1: write access * bit 2 == 0: kernel-mode access 1: user-mode access * bit 3 == 1: use of reserved bit detected * bit 4 == 1: fault was an instruction fetch */ enum x86_pf_error_code { PF_PROT = 1 << 0, PF_WRITE = 1 << 1, PF_USER = 1 << 2, PF_RSVD = 1 << 3, PF_INSTR = 1 << 4, }; /* * Returns 0 if mmiotrace is disabled, or if the fault is not * handled by mmiotrace: */ static inline int kmmio_fault(struct pt_regs *regs, unsigned long addr) { if (unlikely(is_kmmio_active())) if (kmmio_handler(regs, addr) == 1) return -1; return 0; } static inline int notify_page_fault(struct pt_regs *regs) { int ret = 0; /* kprobe_running() needs smp_processor_id() */ if (kprobes_built_in() && !user_mode_vm(regs)) { preempt_disable(); if (kprobe_running() && kprobe_fault_handler(regs, 14)) ret = 1; preempt_enable(); } return ret; } /* * Prefetch quirks: * * 32-bit mode: * * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. * Check that here and ignore it. * * 64-bit mode: * * Sometimes the CPU reports invalid exceptions on prefetch. * Check that here and ignore it. * * Opcode checker based on code by Richard Brunner. */ static inline int check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr, unsigned char opcode, int *prefetch) { unsigned char instr_hi = opcode & 0xf0; unsigned char instr_lo = opcode & 0x0f; switch (instr_hi) { case 0x20: case 0x30: /* * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. * In X86_64 long mode, the CPU will signal invalid * opcode if some of these prefixes are present so * X86_64 will never get here anyway */ return ((instr_lo & 7) == 0x6); #ifdef CONFIG_X86_64 case 0x40: /* * In AMD64 long mode 0x40..0x4F are valid REX prefixes * Need to figure out under what instruction mode the * instruction was issued. Could check the LDT for lm, * but for now it's good enough to assume that long * mode only uses well known segments or kernel. */ return (!user_mode(regs)) || (regs->cs == __USER_CS); #endif case 0x60: /* 0x64 thru 0x67 are valid prefixes in all modes. */ return (instr_lo & 0xC) == 0x4; case 0xF0: /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */ return !instr_lo || (instr_lo>>1) == 1; case 0x00: /* Prefetch instruction is 0x0F0D or 0x0F18 */ if (probe_kernel_address(instr, opcode)) return 0; *prefetch = (instr_lo == 0xF) && (opcode == 0x0D || opcode == 0x18); return 0; default: return 0; } } static int is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) { unsigned char *max_instr; unsigned char *instr; int prefetch = 0; /* * If it was a exec (instruction fetch) fault on NX page, then * do not ignore the fault: */ if (error_code & PF_INSTR) return 0; instr = (void *)convert_ip_to_linear(current, regs); max_instr = instr + 15; if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE) return 0; while (instr < max_instr) { unsigned char opcode; if (probe_kernel_address(instr, opcode)) break; instr++; if (!check_prefetch_opcode(regs, instr, opcode, &prefetch)) break; } return prefetch; } static 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); } DEFINE_SPINLOCK(pgd_lock); LIST_HEAD(pgd_list); #ifdef CONFIG_X86_32 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); else BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k)); return pmd_k; } void vmalloc_sync_all(void) { unsigned long address; if (SHARED_KERNEL_PMD) return; for (address = VMALLOC_START & PMD_MASK; address >= TASK_SIZE && address < FIXADDR_TOP; address += PMD_SIZE) { unsigned long flags; struct page *page; spin_lock_irqsave(&pgd_lock, flags); list_for_each_entry(page, &pgd_list, lru) { if (!vmalloc_sync_one(page_address(page), address)) break; } spin_unlock_irqrestore(&pgd_lock, flags); } } /* * 32-bit: * * Handle a fault on the vmalloc or module mapping area */ static noinline int vmalloc_fault(unsigned long address) { unsigned long pgd_paddr; pmd_t *pmd_k; pte_t *pte_k; /* Make sure we are in vmalloc area: */ if (!(address >= VMALLOC_START && address < VMALLOC_END)) return -1; /* * 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; } /* * Did it hit the DOS screen memory VA from vm86 mode? */ static inline void check_v8086_mode(struct pt_regs *regs, unsigned long address, struct task_struct *tsk) { unsigned long bit; if (!v8086_mode(regs)) return; bit = (address - 0xA0000) >> PAGE_SHIFT; if (bit < 32) tsk->thread.screen_bitmap |= 1 << bit; } static void dump_pagetable(unsigned long address) { __typeof__(pte_val(__pte(0))) page; 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_CONT "*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_PSE)) { 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"); } #else /* CONFIG_X86_64: */ void vmalloc_sync_all(void) { unsigned long address; for (address = VMALLOC_START & PGDIR_MASK; address <= VMALLOC_END; address += PGDIR_SIZE) { const pgd_t *pgd_ref = pgd_offset_k(address); unsigned long flags; struct page *page; if (pgd_none(*pgd_ref)) continue; spin_lock_irqsave(&pgd_lock, flags); list_for_each_entry(page, &pgd_list, lru) { pgd_t *pgd; pgd = (pgd_t *)page_address(page) + pgd_index(address); if (pgd_none(*pgd)) set_pgd(pgd, *pgd_ref); else BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref)); } spin_unlock_irqrestore(&pgd_lock, flags); } } /* * 64-bit: * * Handle a fault on the vmalloc area * * This assumes no large pages in there. */ static noinline int vmalloc_fault(unsigned long address) { pgd_t *pgd, *pgd_ref; pud_t *pud, *pud_ref; pmd_t *pmd, *pmd_ref; pte_t *pte, *pte_ref; /* Make sure we are in vmalloc area: */ if (!(address >= VMALLOC_START && address < VMALLOC_END)) return -1; /* * Copy kernel mappings over when needed. This can also * happen within a race in page table update. In the later * case just flush: */ pgd = pgd_offset(current->active_mm, address); pgd_ref = pgd_offset_k(address); if (pgd_none(*pgd_ref)) return -1; if (pgd_none(*pgd)) set_pgd(pgd, *pgd_ref); else BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref)); /* * Below here mismatches are bugs because these lower tables * are shared: */ pud = pud_offset(pgd, address); pud_ref = pud_offset(pgd_ref, address); if (pud_none(*pud_ref)) return -1; if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref)) BUG(); pmd = pmd_offset(pud, address); pmd_ref = pmd_offset(pud_ref, address); if (pmd_none(*pmd_ref)) return -1; if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref)) BUG(); pte_ref = pte_offset_kernel(pmd_ref, address); if (!pte_present(*pte_ref)) return -1; pte = pte_offset_kernel(pmd, address); /* * Don't use pte_page here, because the mappings can point * outside mem_map, and the NUMA hash lookup cannot handle * that: */ if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref)) BUG(); return 0; } static const char errata93_warning[] = KERN_ERR "******* Your BIOS seems to not contain a fix for K8 errata #93\n" KERN_ERR "******* Working around it, but it may cause SEGVs or burn power.\n" KERN_ERR "******* Please consider a BIOS update.\n" KERN_ERR "******* Disabling USB legacy in the BIOS may also help.\n"; /* * No vm86 mode in 64-bit mode: */ static inline void check_v8086_mode(struct pt_regs *regs, unsigned long address, struct task_struct *tsk) { } static int bad_address(void *p) { unsigned long dummy; return probe_kernel_address((unsigned long *)p, dummy); } static void dump_pagetable(unsigned long address) { pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t *pte; pgd = (pgd_t *)read_cr3(); pgd = __va((unsigned long)pgd & PHYSICAL_PAGE_MASK); pgd += pgd_index(address); if (bad_address(pgd)) goto bad; printk("PGD %lx ", pgd_val(*pgd)); if (!pgd_present(*pgd)) goto out; pud = pud_offset(pgd, address); if (bad_address(pud)) goto bad; printk("PUD %lx ", pud_val(*pud)); if (!pud_present(*pud) || pud_large(*pud)) goto out; pmd = pmd_offset(pud, address); if (bad_address(pmd)) goto bad; printk("PMD %lx ", pmd_val(*pmd)); if (!pmd_present(*pmd) || pmd_large(*pmd)) goto out; pte = pte_offset_kernel(pmd, address); if (bad_address(pte)) goto bad; printk("PTE %lx", pte_val(*pte)); out: printk("\n"); return; bad: printk("BAD\n"); } #endif /* CONFIG_X86_64 */ /* * Workaround for K8 erratum #93 & buggy BIOS. * * BIOS SMM functions are required to use a specific workaround * to avoid corruption of the 64bit RIP register on C stepping K8. * * A lot of BIOS that didn't get tested properly miss this. * * The OS sees this as a page fault with the upper 32bits of RIP cleared. * Try to work around it here. * * Note we only handle faults in kernel here. * Does nothing on 32-bit. */ static int is_errata93(struct pt_regs *regs, unsigned long address) { #ifdef CONFIG_X86_64 static int once; if (address != regs->ip) return 0; if ((address >> 32) != 0) return 0; address |= 0xffffffffUL << 32; if ((address >= (u64)_stext && address <= (u64)_etext) || (address >= MODULES_VADDR && address <= MODULES_END)) { if (!once) { printk(errata93_warning); once = 1; } regs->ip = address; return 1; } #endif return 0; } /* * Work around K8 erratum #100 K8 in compat mode occasionally jumps * to illegal addresses >4GB. * * We catch this in the page fault handler because these addresses * are not reachable. Just detect this case and return. Any code * segment in LDT is compatibility mode. */ static int is_errata100(struct pt_regs *regs, unsigned long address) { #ifdef CONFIG_X86_64 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32)) return 1; #endif return 0; } static int is_f00f_bug(struct pt_regs *regs, unsigned long address) { #ifdef CONFIG_X86_F00F_BUG unsigned long nr; /* * Pentium F0 0F C7 C8 bug workaround: */ if (boot_cpu_data.f00f_bug) { nr = (address - idt_descr.address) >> 3; if (nr == 6) { do_invalid_op(regs, 0); return 1; } } #endif return 0; } static const char nx_warning[] = KERN_CRIT "kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n"; static void show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address) { if (!oops_may_print()) return; if (error_code & PF_INSTR) { unsigned int level; pte_t *pte = lookup_address(address, &level); if (pte && pte_present(*pte) && !pte_exec(*pte)) printk(nx_warning, current_uid()); } printk(KERN_ALERT "BUG: unable to handle kernel "); if (address < PAGE_SIZE) printk(KERN_CONT "NULL pointer dereference"); else printk(KERN_CONT "paging request"); printk(KERN_CONT " at %p\n", (void *) address); printk(KERN_ALERT "IP:"); printk_address(regs->ip, 1); dump_pagetable(address); } static noinline void pgtable_bad(struct pt_regs *regs, unsigned long error_code, unsigned long address) { struct task_struct *tsk; unsigned long flags; int sig; flags = oops_begin(); tsk = current; sig = SIGKILL; printk(KERN_ALERT "%s: Corrupted page table at address %lx\n", tsk->comm, address); dump_pagetable(address); tsk->thread.cr2 = address; tsk->thread.trap_no = 14; tsk->thread.error_code = error_code; if (__die("Bad pagetable", regs, error_code)) sig = 0; oops_end(flags, regs, sig); } static noinline void no_context(struct pt_regs *regs, unsigned long error_code, unsigned long address) { struct task_struct *tsk = current; unsigned long *stackend; unsigned long flags; int sig; /* Are we prepared to handle this kernel fault? */ if (fixup_exception(regs)) return; /* * 32-bit: * * Valid to do another page fault here, because if this fault * had been triggered by is_prefetch fixup_exception would have * handled it. * * 64-bit: * * Hall of shame of CPU/BIOS bugs. */ if (is_prefetch(regs, error_code, address)) return; if (is_errata93(regs, address)) return; /* * Oops. The kernel tried to access some bad page. We'll have to * terminate things with extreme prejudice: */ flags = oops_begin(); show_fault_oops(regs, error_code, address); stackend = end_of_stack(tsk); if (*stackend != STACK_END_MAGIC) printk(KERN_ALERT "Thread overran stack, or stack corrupted\n"); tsk->thread.cr2 = address; tsk->thread.trap_no = 14; tsk->thread.error_code = error_code; sig = SIGKILL; if (__die("Oops", regs, error_code)) sig = 0; /* Executive summary in case the body of the oops scrolled away */ printk(KERN_EMERG "CR2: %016lx\n", address); oops_end(flags, regs, sig); } /* * Print out info about fatal segfaults, if the show_unhandled_signals * sysctl is set: */ static inline void show_signal_msg(struct pt_regs *regs, unsigned long error_code, unsigned long address, struct task_struct *tsk) { if (!unhandled_signal(tsk, SIGSEGV)) return; if (!printk_ratelimit()) return; printk(KERN_CONT "%s%s[%d]: segfault at %lx ip %p sp %p error %lx", task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG, tsk->comm, task_pid_nr(tsk), address, (void *)regs->ip, (void *)regs->sp, error_code); print_vma_addr(KERN_CONT " in ", regs->ip); printk(KERN_CONT "\n"); } static void __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, unsigned long address, int si_code) { struct task_struct *tsk = current; /* User mode accesses just cause a SIGSEGV */ if (error_code & PF_USER) { /* * 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, error_code, address)) return; if (is_errata100(regs, address)) return; if (unlikely(show_unhandled_signals)) show_signal_msg(regs, error_code, address, tsk); /* Kernel addresses are always protection faults: */ tsk->thread.cr2 = address; tsk->thread.error_code = error_code | (address >= TASK_SIZE); tsk->thread.trap_no = 14; force_sig_info_fault(SIGSEGV, si_code, address, tsk); return; } if (is_f00f_bug(regs, address)) return; no_context(regs, error_code, address); } static noinline void bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, unsigned long address) { __bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR); } static void __bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address, int si_code) { struct mm_struct *mm = current->mm; /* * Something tried to access memory that isn't in our memory map.. * Fix it, but check if it's kernel or user first.. */ up_read(&mm->mmap_sem); __bad_area_nosemaphore(regs, error_code, address, si_code); } static noinline void bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address) { __bad_area(regs, error_code, address, SEGV_MAPERR); } static noinline void bad_area_access_error(struct pt_regs *regs, unsigned long error_code, unsigned long address) { __bad_area(regs, error_code, address, SEGV_ACCERR); } /* TODO: fixup for "mm-invoke-oom-killer-from-page-fault.patch" */ static void out_of_memory(struct pt_regs *regs, unsigned long error_code, unsigned long address) { /* * We ran out of memory, call the OOM killer, and return the userspace * (which will retry the fault, or kill us if we got oom-killed): */ up_read(¤t->mm->mmap_sem); pagefault_out_of_memory(); } static void do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address) { struct task_struct *tsk = current; struct mm_struct *mm = tsk->mm; up_read(&mm->mmap_sem); /* Kernel mode? Handle exceptions or die: */ if (!(error_code & PF_USER)) no_context(regs, error_code, address); /* User-space => ok to do another page fault: */ if (is_prefetch(regs, error_code, address)) 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); } static noinline void mm_fault_error(struct pt_regs *regs, unsigned long error_code, unsigned long address, unsigned int fault) { if (fault & VM_FAULT_OOM) { out_of_memory(regs, error_code, address); } else { if (fault & VM_FAULT_SIGBUS) do_sigbus(regs, error_code, address); else BUG(); } } static int spurious_fault_check(unsigned long error_code, pte_t *pte) { if ((error_code & PF_WRITE) && !pte_write(*pte)) return 0; if ((error_code & PF_INSTR) && !pte_exec(*pte)) return 0; return 1; } /* * Handle a spurious fault caused by a stale TLB entry. * * This allows us to lazily refresh the TLB when increasing the * permissions of a kernel page (RO -> RW or NX -> X). Doing it * eagerly is very expensive since that implies doing a full * cross-processor TLB flush, even if no stale TLB entries exist * on other processors. * * There are no security implications to leaving a stale TLB when * increasing the permissions on a page. */ static noinline int spurious_fault(unsigned long error_code, unsigned long address) { pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t *pte; int ret; /* Reserved-bit violation or user access to kernel space? */ if (error_code & (PF_USER | PF_RSVD)) return 0; pgd = init_mm.pgd + pgd_index(address); if (!pgd_present(*pgd)) return 0; pud = pud_offset(pgd, address); if (!pud_present(*pud)) return 0; if (pud_large(*pud)) return spurious_fault_check(error_code, (pte_t *) pud); pmd = pmd_offset(pud, address); if (!pmd_present(*pmd)) return 0; if (pmd_large(*pmd)) return spurious_fault_check(error_code, (pte_t *) pmd); pte = pte_offset_kernel(pmd, address); if (!pte_present(*pte)) return 0; ret = spurious_fault_check(error_code, pte); if (!ret) return 0; /* * Make sure we have permissions in PMD. * If not, then there's a bug in the page tables: */ ret = spurious_fault_check(error_code, (pte_t *) pmd); WARN_ONCE(!ret, "PMD has incorrect permission bits\n"); return ret; } int show_unhandled_signals = 1; static inline int access_error(unsigned long error_code, int write, struct vm_area_struct *vma) { if (write) { /* write, present and write, not present: */ if (unlikely(!(vma->vm_flags & VM_WRITE))) return 1; return 0; } /* read, present: */ if (unlikely(error_code & PF_PROT)) return 1; /* read, not present: */ if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))) return 1; return 0; } static int fault_in_kernel_space(unsigned long address) { return address >= TASK_SIZE_MAX; } /* * This routine handles page faults. It determines the address, * and the problem, and then passes it off to one of the appropriate * routines. */ dotraplinkage void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code) { struct vm_area_struct *vma; struct task_struct *tsk; unsigned long address; struct mm_struct *mm; int write; int fault; tsk = current; mm = tsk->mm; prefetchw(&mm->mmap_sem); /* Get the faulting address: */ address = read_cr2(); if (unlikely(kmmio_fault(regs, address))) return; /* * 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(fault_in_kernel_space(address))) { if (!(error_code & (PF_RSVD|PF_USER|PF_PROT)) && vmalloc_fault(address) >= 0) return; /* Can handle a stale RO->RW TLB: */ if (spurious_fault(error_code, address)) return; /* kprobes don't want to hook the spurious faults: */ if (notify_page_fault(regs)) return; /* * Don't take the mm semaphore here. If we fixup a prefetch * fault we could otherwise deadlock: */ bad_area_nosemaphore(regs, error_code, address); return; } /* kprobes don't want to hook the spurious faults: */ if (unlikely(notify_page_fault(regs))) return; /* * It's safe to allow irq's after cr2 has been saved and the * vmalloc fault has been handled. * * User-mode registers count as a user access even for any * potential system fault or CPU buglet: */ if (user_mode_vm(regs)) { local_irq_enable(); error_code |= PF_USER; } else { if (regs->flags & X86_EFLAGS_IF) local_irq_enable(); } if (unlikely(error_code & PF_RSVD)) pgtable_bad(regs, error_code, address); /* * 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 (unlikely(in_atomic() || !mm)) { bad_area_nosemaphore(regs, error_code, address); return; } /* * 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 (unlikely(!down_read_trylock(&mm->mmap_sem))) { if ((error_code & PF_USER) == 0 && !search_exception_tables(regs->ip)) { bad_area_nosemaphore(regs, error_code, address); return; } down_read(&mm->mmap_sem); } else { /* * The above down_read_trylock() might have succeeded in * which case we'll have missed the might_sleep() from * down_read(): */ might_sleep(); } vma = find_vma(mm, address); if (unlikely(!vma)) { bad_area(regs, error_code, address); return; } if (likely(vma->vm_start <= address)) goto good_area; if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) { bad_area(regs, error_code, address); return; } if (error_code & PF_USER) { /* * Accessing the stack below %sp is always a bug. * The large cushion allows instructions like enter * and pusha to work. ("enter $65535, $31" pushes * 32 pointers and then decrements %sp by 65535.) */ if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) { bad_area(regs, error_code, address); return; } } if (unlikely(expand_stack(vma, address))) { bad_area(regs, error_code, address); return; } /* * Ok, we have a good vm_area for this memory access, so * we can handle it.. */ good_area: write = error_code & PF_WRITE; if (unlikely(access_error(error_code, write, vma))) { bad_area_access_error(regs, error_code, address); return; } /* * 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)) { mm_fault_error(regs, error_code, address, fault); return; } if (fault & VM_FAULT_MAJOR) tsk->maj_flt++; else tsk->min_flt++; check_v8086_mode(regs, address, tsk); up_read(&mm->mmap_sem); }