/*
* linux/arch/i386/mm/fault.c
*
* Copyright (C) 1995 Linus Torvalds
*/
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/tty.h>
#include <linux/vt_kern.h> /* For unblank_screen() */
#include <linux/highmem.h>
#include <linux/bootmem.h> /* for max_low_pfn */
#include <linux/vmalloc.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
#include <asm/system.h>
#include <asm/desc.h>
#include <asm/segment.h>
extern void die(const char *,struct pt_regs *,long);
static ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);
int register_page_fault_notifier(struct notifier_block *nb)
{
vmalloc_sync_all();
return atomic_notifier_chain_register(¬ify_page_fault_chain, nb);
}
EXPORT_SYMBOL_GPL(register_page_fault_notifier);
int unregister_page_fault_notifier(struct notifier_block *nb)
{
return atomic_notifier_chain_unregister(¬ify_page_fault_chain, nb);
}
EXPORT_SYMBOL_GPL(unregister_page_fault_notifier);
static inline int notify_page_fault(struct pt_regs *regs, long err)
{
struct die_args args = {
.regs = regs,
.str = "page fault",
.err = err,
.trapnr = 14,
.signr = SIGSEGV
};
return atomic_notifier_call_chain(¬ify_page_fault_chain,
DIE_PAGE_FAULT, &args);
}
/*
* 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. */
down(¤t->mm->context.sem);
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)) {
up(¤t->mm->context.sem);
} 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);
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;
}
/*
* 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;
/* 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, error_code) == NOTIFY_STOP)
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, error_code) == NOTIFY_STOP)
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. Unfortunatly, 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 possibilty 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.
*/
switch (handle_mm_fault(mm, vma, address, write)) {
case VM_FAULT_MINOR:
tsk->min_flt++;
break;
case VM_FAULT_MAJOR:
tsk->maj_flt++;
break;
case VM_FAULT_SIGBUS:
goto do_sigbus;
case VM_FAULT_OOM:
goto out_of_memory;
default:
BUG();
}
/*
* 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) {
/*
* Valid to do another page fault here because this one came
* from user space.
*/
if (is_prefetch(regs, address, error_code))
return;
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:\n");
printk("%08lx\n", regs->eip);
page = read_cr3();
page = ((__typeof__(page) *) __va(page))[address >> PGDIR_SHIFT];
#ifdef CONFIG_X86_PAE
printk(KERN_ALERT "*pdpt = %016Lx\n", 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\n", page);
page &= ~_PAGE_NX;
}
#else
printk(KERN_ALERT "*pde = %08lx\n", 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(KERN_ALERT "*pte = %0*Lx\n", sizeof(page)*2, (u64)page);
}
}
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_init(tsk)) {
yield();
down_read(&mm->mmap_sem);
goto survive;
}
printk("VM: killing process %s\n", tsk->comm);
if (error_code & 4)
do_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;
}
}
