/* * Copyright (C) 1995 Linus Torvalds * Copyright (C) 2001,2002 Andi Kleen, SuSE Labs. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* For unblank_screen() */ #include #include #include #include #include #include #include #include #include #include #include #include /* * Page fault error code bits * 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 */ #define PF_PROT (1<<0) #define PF_WRITE (1<<1) #define PF_USER (1<<2) #define PF_RSVD (1<<3) #define PF_INSTR (1<<4) static inline int notify_page_fault(struct pt_regs *regs) { #ifdef CONFIG_KPROBES int ret = 0; /* kprobe_running() needs smp_processor_id() */ if (!user_mode(regs)) { preempt_disable(); if (kprobe_running() && kprobe_fault_handler(regs, 14)) ret = 1; preempt_enable(); } return ret; #else return 0; #endif } #ifdef CONFIG_X86_32 /* * 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 ip = regs->ip; unsigned seg = regs->cs & 0xffff; u32 seg_ar, seg_limit, base, *desc; /* Unlikely, but must come before segment checks. */ if (unlikely(regs->flags & VM_MASK)) { base = seg << 4; *eip_limit = base + 0xffff; return base + (ip & 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 ip; /* 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) || ip > seg_limit) { *eip_limit = 0; return 1; /* So that returned ip > *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((struct desc_struct *)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 ip + base; } #endif /* * X86_32 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. * Check that here and ignore it. * * X86_64 * Sometimes the CPU reports invalid exceptions on prefetch. * Check that here and ignore it. * * Opcode checker based on code by Richard Brunner */ static int is_prefetch(struct pt_regs *regs, unsigned long addr, unsigned long error_code) { unsigned char *instr; int scan_more = 1; int prefetch = 0; unsigned char *max_instr; #ifdef CONFIG_X86_32 unsigned long limit; 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 & PF_INSTR)) return 0; } else { return 0; } instr = (unsigned char *)get_segment_eip(regs, &limit); #else /* If it was a exec fault ignore */ if (error_code & PF_INSTR) return 0; instr = (unsigned char __user *)convert_rip_to_linear(current, regs); #endif max_instr = instr + 15; #ifdef CONFIG_X86_64 if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE) return 0; #endif while (scan_more && instr < max_instr) { unsigned char opcode; unsigned char instr_hi; unsigned char instr_lo; #ifdef CONFIG_X86_32 if (instr > (unsigned char *)limit) break; #endif 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. * 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 */ scan_more = ((instr_lo & 7) == 0x6); break; #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. */ scan_more = (!user_mode(regs)) || (regs->cs == __USER_CS); break; #endif case 0x60: /* 0x64 thru 0x67 are valid prefixes in all modes. */ scan_more = (instr_lo & 0xC) == 0x4; break; case 0xF0: /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */ scan_more = !instr_lo || (instr_lo>>1) == 1; break; case 0x00: /* Prefetch instruction is 0x0F0D or 0x0F18 */ scan_more = 0; #ifdef CONFIG_X86_32 if (instr > (unsigned char *)limit) break; #endif if (probe_kernel_address(instr, opcode)) break; prefetch = (instr_lo == 0xF) && (opcode == 0x0D || opcode == 0x18); break; default: scan_more = 0; 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); } static int bad_address(void *p) { unsigned long dummy; return probe_kernel_address((unsigned long *)p, dummy); } 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 ret; pud = pud_offset(pgd, address); if (bad_address(pud)) goto bad; printk("PUD %lx ", pud_val(*pud)); if (!pud_present(*pud)) goto ret; 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 ret; pte = pte_offset_kernel(pmd, address); if (bad_address(pte)) goto bad; printk("PTE %lx", pte_val(*pte)); ret: printk("\n"); return; bad: printk("BAD\n"); } #ifdef CONFIG_X86_64 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"; /* 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. */ static int is_errata93(struct pt_regs *regs, unsigned long address) { static int warned; 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 (!warned) { printk(errata93_warning); warned = 1; } regs->ip = address; return 1; } return 0; } #endif static noinline void pgtable_bad(unsigned long address, struct pt_regs *regs, unsigned long error_code) { unsigned long flags = oops_begin(); struct task_struct *tsk; printk(KERN_ALERT "%s: Corrupted page table at address %lx\n", current->comm, address); dump_pagetable(address); tsk = current; tsk->thread.cr2 = address; tsk->thread.trap_no = 14; tsk->thread.error_code = error_code; if (__die("Bad pagetable", regs, error_code)) regs = NULL; oops_end(flags, regs, SIGKILL); } /* * Handle a fault on the vmalloc area * * This assumes no large pages in there. */ static 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; /* 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->mm ?: &init_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; } 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. */ asmlinkage 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, fault; unsigned long flags; int si_code; /* * We can fault from pretty much anywhere, with unknown IRQ state. */ trace_hardirqs_fixup(); tsk = current; mm = tsk->mm; prefetchw(&mm->mmap_sem); /* get the address */ address = read_cr2(); 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_SIZE64)) { /* * Don't check for the module range here: its PML4 * is always initialized because it's shared with the main * kernel text. Only vmalloc may need PML4 syncups. */ if (!(error_code & (PF_RSVD|PF_USER|PF_PROT)) && ((address >= VMALLOC_START && address < VMALLOC_END))) { if (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; if (likely(regs->flags & X86_EFLAGS_IF)) local_irq_enable(); if (unlikely(error_code & PF_RSVD)) pgtable_bad(address, regs, error_code); /* * 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)) goto bad_area_nosemaphore; /* * User-mode registers count as a user access even for any * potential system fault or CPU buglet. */ if (user_mode_vm(regs)) error_code |= PF_USER; again: /* 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 & PF_USER) == 0 && !search_exception_tables(regs->ip)) goto bad_area_nosemaphore; down_read(&mm->mmap_sem); } vma = find_vma(mm, address); if (!vma) goto bad_area; if (likely(vma->vm_start <= address)) goto good_area; if (!(vma->vm_flags & VM_GROWSDOWN)) goto bad_area; if (error_code & PF_USER) { /* Allow userspace just enough access below the stack pointer * to let the 'enter' instruction work. */ if (address + 65536 + 32 * sizeof(unsigned long) < regs->sp) 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 & (PF_PROT|PF_WRITE)) { default: /* 3: write, present */ /* fall through */ case PF_WRITE: /* write, not present */ if (!(vma->vm_flags & VM_WRITE)) goto bad_area; write++; break; case PF_PROT: /* read, present */ goto bad_area; case 0: /* read, not present */ if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))) goto bad_area; } /* * 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++; 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 & PF_USER) { /* * It's possible to have interrupts off here. */ local_irq_enable(); if (is_prefetch(regs, address, error_code)) return; /* Work around K8 erratum #100 K8 in compat mode occasionally jumps to illegal addresses >4GB. We catch this here 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. */ if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32)) return; if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) && printk_ratelimit()) { printk( "%s%s[%d]: segfault at %lx ip %lx sp %lx error %lx\n", tsk->pid > 1 ? KERN_INFO : KERN_EMERG, tsk->comm, tsk->pid, address, regs->ip, regs->sp, 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; } no_context: /* Are we prepared to handle this kernel fault? */ if (fixup_exception(regs)) return; /* * Hall of shame of CPU/BIOS bugs. */ if (is_prefetch(regs, address, error_code)) 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(); if (address < PAGE_SIZE) printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference"); else printk(KERN_ALERT "Unable to handle kernel paging request"); printk(" at %016lx RIP: \n" KERN_ALERT, address); printk_address(regs->ip); dump_pagetable(address); tsk->thread.cr2 = address; tsk->thread.trap_no = 14; tsk->thread.error_code = error_code; if (__die("Oops", regs, error_code)) regs = NULL; /* Executive summary in case the body of the oops scrolled away */ printk(KERN_EMERG "CR2: %016lx\n", address); oops_end(flags, regs, 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(current)) { yield(); goto again; } 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 & PF_USER)) goto no_context; tsk->thread.cr2 = address; tsk->thread.error_code = error_code; tsk->thread.trap_no = 14; force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk); return; } DEFINE_SPINLOCK(pgd_lock); LIST_HEAD(pgd_list); 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 = VMALLOC_START & PGDIR_MASK; unsigned long address; for (address = start; address <= VMALLOC_END; address += PGDIR_SIZE) { if (!test_bit(pgd_index(address), insync)) { const pgd_t *pgd_ref = pgd_offset_k(address); struct page *page; if (pgd_none(*pgd_ref)) continue; spin_lock(&pgd_lock); 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(&pgd_lock); set_bit(pgd_index(address), insync); } if (address == start) start = address + PGDIR_SIZE; } /* Check that there is no need to do the same for the modules area. */ BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL)); BUILD_BUG_ON(!(((MODULES_END - 1) & PGDIR_MASK) == (__START_KERNEL & PGDIR_MASK))); }