linux/arch/x86/mm/fault.c
Linus Torvalds 643ad15d47 Merge branch 'mm-pkeys-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 protection key support from Ingo Molnar:
 "This tree adds support for a new memory protection hardware feature
  that is available in upcoming Intel CPUs: 'protection keys' (pkeys).

  There's a background article at LWN.net:

      https://lwn.net/Articles/643797/

  The gist is that protection keys allow the encoding of
  user-controllable permission masks in the pte.  So instead of having a
  fixed protection mask in the pte (which needs a system call to change
  and works on a per page basis), the user can map a (handful of)
  protection mask variants and can change the masks runtime relatively
  cheaply, without having to change every single page in the affected
  virtual memory range.

  This allows the dynamic switching of the protection bits of large
  amounts of virtual memory, via user-space instructions.  It also
  allows more precise control of MMU permission bits: for example the
  executable bit is separate from the read bit (see more about that
  below).

  This tree adds the MM infrastructure and low level x86 glue needed for
  that, plus it adds a high level API to make use of protection keys -
  if a user-space application calls:

        mmap(..., PROT_EXEC);

  or

        mprotect(ptr, sz, PROT_EXEC);

  (note PROT_EXEC-only, without PROT_READ/WRITE), the kernel will notice
  this special case, and will set a special protection key on this
  memory range.  It also sets the appropriate bits in the Protection
  Keys User Rights (PKRU) register so that the memory becomes unreadable
  and unwritable.

  So using protection keys the kernel is able to implement 'true'
  PROT_EXEC on x86 CPUs: without protection keys PROT_EXEC implies
  PROT_READ as well.  Unreadable executable mappings have security
  advantages: they cannot be read via information leaks to figure out
  ASLR details, nor can they be scanned for ROP gadgets - and they
  cannot be used by exploits for data purposes either.

  We know about no user-space code that relies on pure PROT_EXEC
  mappings today, but binary loaders could start making use of this new
  feature to map binaries and libraries in a more secure fashion.

  There is other pending pkeys work that offers more high level system
  call APIs to manage protection keys - but those are not part of this
  pull request.

  Right now there's a Kconfig that controls this feature
  (CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) that is default enabled
  (like most x86 CPU feature enablement code that has no runtime
  overhead), but it's not user-configurable at the moment.  If there's
  any serious problem with this then we can make it configurable and/or
  flip the default"

* 'mm-pkeys-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (38 commits)
  x86/mm/pkeys: Fix mismerge of protection keys CPUID bits
  mm/pkeys: Fix siginfo ABI breakage caused by new u64 field
  x86/mm/pkeys: Fix access_error() denial of writes to write-only VMA
  mm/core, x86/mm/pkeys: Add execute-only protection keys support
  x86/mm/pkeys: Create an x86 arch_calc_vm_prot_bits() for VMA flags
  x86/mm/pkeys: Allow kernel to modify user pkey rights register
  x86/fpu: Allow setting of XSAVE state
  x86/mm: Factor out LDT init from context init
  mm/core, x86/mm/pkeys: Add arch_validate_pkey()
  mm/core, arch, powerpc: Pass a protection key in to calc_vm_flag_bits()
  x86/mm/pkeys: Actually enable Memory Protection Keys in the CPU
  x86/mm/pkeys: Add Kconfig prompt to existing config option
  x86/mm/pkeys: Dump pkey from VMA in /proc/pid/smaps
  x86/mm/pkeys: Dump PKRU with other kernel registers
  mm/core, x86/mm/pkeys: Differentiate instruction fetches
  x86/mm/pkeys: Optimize fault handling in access_error()
  mm/core: Do not enforce PKEY permissions on remote mm access
  um, pkeys: Add UML arch_*_access_permitted() methods
  mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys
  x86/mm/gup: Simplify get_user_pages() PTE bit handling
  ...
2016-03-20 19:08:56 -07:00

1449 lines
36 KiB
C

/*
* Copyright (C) 1995 Linus Torvalds
* Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs.
* Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar
*/
#include <linux/sched.h> /* test_thread_flag(), ... */
#include <linux/kdebug.h> /* oops_begin/end, ... */
#include <linux/module.h> /* search_exception_table */
#include <linux/bootmem.h> /* max_low_pfn */
#include <linux/kprobes.h> /* NOKPROBE_SYMBOL, ... */
#include <linux/mmiotrace.h> /* kmmio_handler, ... */
#include <linux/perf_event.h> /* perf_sw_event */
#include <linux/hugetlb.h> /* hstate_index_to_shift */
#include <linux/prefetch.h> /* prefetchw */
#include <linux/context_tracking.h> /* exception_enter(), ... */
#include <linux/uaccess.h> /* faulthandler_disabled() */
#include <asm/cpufeature.h> /* boot_cpu_has, ... */
#include <asm/traps.h> /* dotraplinkage, ... */
#include <asm/pgalloc.h> /* pgd_*(), ... */
#include <asm/kmemcheck.h> /* kmemcheck_*(), ... */
#include <asm/fixmap.h> /* VSYSCALL_ADDR */
#include <asm/vsyscall.h> /* emulate_vsyscall */
#include <asm/vm86.h> /* struct vm86 */
#include <asm/mmu_context.h> /* vma_pkey() */
#define CREATE_TRACE_POINTS
#include <asm/trace/exceptions.h>
/*
* 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
* bit 5 == 1: protection keys block access
*/
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,
PF_PK = 1 << 5,
};
/*
* Returns 0 if mmiotrace is disabled, or if the fault is not
* handled by mmiotrace:
*/
static nokprobe_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 nokprobe_inline int kprobes_fault(struct pt_regs *regs)
{
int ret = 0;
/* kprobe_running() needs smp_processor_id() */
if (kprobes_built_in() && !user_mode(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) || user_64bit_mode(regs));
#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_MAX)
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;
}
/*
* A protection key fault means that the PKRU value did not allow
* access to some PTE. Userspace can figure out what PKRU was
* from the XSAVE state, and this function fills out a field in
* siginfo so userspace can discover which protection key was set
* on the PTE.
*
* If we get here, we know that the hardware signaled a PF_PK
* fault and that there was a VMA once we got in the fault
* handler. It does *not* guarantee that the VMA we find here
* was the one that we faulted on.
*
* 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
* 2. T1 : set PKRU to deny access to pkey=4, touches page
* 3. T1 : faults...
* 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
* 5. T1 : enters fault handler, takes mmap_sem, etc...
* 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
* faulted on a pte with its pkey=4.
*/
static void fill_sig_info_pkey(int si_code, siginfo_t *info,
struct vm_area_struct *vma)
{
/* This is effectively an #ifdef */
if (!boot_cpu_has(X86_FEATURE_OSPKE))
return;
/* Fault not from Protection Keys: nothing to do */
if (si_code != SEGV_PKUERR)
return;
/*
* force_sig_info_fault() is called from a number of
* contexts, some of which have a VMA and some of which
* do not. The PF_PK handing happens after we have a
* valid VMA, so we should never reach this without a
* valid VMA.
*/
if (!vma) {
WARN_ONCE(1, "PKU fault with no VMA passed in");
info->si_pkey = 0;
return;
}
/*
* si_pkey should be thought of as a strong hint, but not
* absolutely guranteed to be 100% accurate because of
* the race explained above.
*/
info->si_pkey = vma_pkey(vma);
}
static void
force_sig_info_fault(int si_signo, int si_code, unsigned long address,
struct task_struct *tsk, struct vm_area_struct *vma,
int fault)
{
unsigned lsb = 0;
siginfo_t info;
info.si_signo = si_signo;
info.si_errno = 0;
info.si_code = si_code;
info.si_addr = (void __user *)address;
if (fault & VM_FAULT_HWPOISON_LARGE)
lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
if (fault & VM_FAULT_HWPOISON)
lsb = PAGE_SHIFT;
info.si_addr_lsb = lsb;
fill_sig_info_pkey(si_code, &info, vma);
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) {
struct page *page;
spin_lock(&pgd_lock);
list_for_each_entry(page, &pgd_list, lru) {
spinlock_t *pgt_lock;
pmd_t *ret;
/* the pgt_lock only for Xen */
pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
spin_lock(pgt_lock);
ret = vmalloc_sync_one(page_address(page), address);
spin_unlock(pgt_lock);
if (!ret)
break;
}
spin_unlock(&pgd_lock);
}
}
/*
* 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;
WARN_ON_ONCE(in_nmi());
/*
* 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;
if (pmd_huge(*pmd_k))
return 0;
pte_k = pte_offset_kernel(pmd_k, address);
if (!pte_present(*pte_k))
return -1;
return 0;
}
NOKPROBE_SYMBOL(vmalloc_fault);
/*
* 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)
{
#ifdef CONFIG_VM86
unsigned long bit;
if (!v8086_mode(regs) || !tsk->thread.vm86)
return;
bit = (address - 0xA0000) >> PAGE_SHIFT;
if (bit < 32)
tsk->thread.vm86->screen_bitmap |= 1 << bit;
#endif
}
static bool low_pfn(unsigned long pfn)
{
return pfn < max_low_pfn;
}
static void dump_pagetable(unsigned long address)
{
pgd_t *base = __va(read_cr3());
pgd_t *pgd = &base[pgd_index(address)];
pmd_t *pmd;
pte_t *pte;
#ifdef CONFIG_X86_PAE
printk("*pdpt = %016Lx ", pgd_val(*pgd));
if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
goto out;
#endif
pmd = pmd_offset(pud_offset(pgd, address), address);
printk(KERN_CONT "*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));
/*
* 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 (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd))
goto out;
pte = pte_offset_kernel(pmd, address);
printk("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
out:
printk("\n");
}
#else /* CONFIG_X86_64: */
void vmalloc_sync_all(void)
{
sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END, 0);
}
/*
* 64-bit:
*
* Handle a fault on the vmalloc area
*/
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;
WARN_ON_ONCE(in_nmi());
/*
* 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);
arch_flush_lazy_mmu_mode();
} 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_pfn(*pud) != pud_pfn(*pud_ref))
BUG();
if (pud_huge(*pud))
return 0;
pmd = pmd_offset(pud, address);
pmd_ref = pmd_offset(pud_ref, address);
if (pmd_none(*pmd_ref))
return -1;
if (pmd_none(*pmd) || pmd_pfn(*pmd) != pmd_pfn(*pmd_ref))
BUG();
if (pmd_huge(*pmd))
return 0;
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;
}
NOKPROBE_SYMBOL(vmalloc_fault);
#ifdef CONFIG_CPU_SUP_AMD
static const char errata93_warning[] =
KERN_ERR
"******* Your BIOS seems to not contain a fix for K8 errata #93\n"
"******* Working around it, but it may cause SEGVs or burn power.\n"
"******* Please consider a BIOS update.\n"
"******* Disabling USB legacy in the BIOS may also help.\n";
#endif
/*
* 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 *base = __va(read_cr3() & PHYSICAL_PAGE_MASK);
pgd_t *pgd = base + pgd_index(address);
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
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)
{
#if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD)
if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD
|| boot_cpu_data.x86 != 0xf)
return 0;
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)) {
printk_once(errata93_warning);
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_has_bug(X86_BUG_F00F)) {
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 const char smep_warning[] = KERN_CRIT
"unable to execute userspace code (SMEP?) (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;
pgd_t *pgd;
pte_t *pte;
pgd = __va(read_cr3() & PHYSICAL_PAGE_MASK);
pgd += pgd_index(address);
pte = lookup_address_in_pgd(pgd, address, &level);
if (pte && pte_present(*pte) && !pte_exec(*pte))
printk(nx_warning, from_kuid(&init_user_ns, current_uid()));
if (pte && pte_present(*pte) && pte_exec(*pte) &&
(pgd_flags(*pgd) & _PAGE_USER) &&
(__read_cr4() & X86_CR4_SMEP))
printk(smep_warning, from_kuid(&init_user_ns, 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);
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_nr = X86_TRAP_PF;
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, int signal, int si_code)
{
struct task_struct *tsk = current;
unsigned long flags;
int sig;
/* No context means no VMA to pass down */
struct vm_area_struct *vma = NULL;
/* Are we prepared to handle this kernel fault? */
if (fixup_exception(regs, X86_TRAP_PF)) {
/*
* Any interrupt that takes a fault gets the fixup. This makes
* the below recursive fault logic only apply to a faults from
* task context.
*/
if (in_interrupt())
return;
/*
* Per the above we're !in_interrupt(), aka. task context.
*
* In this case we need to make sure we're not recursively
* faulting through the emulate_vsyscall() logic.
*/
if (current_thread_info()->sig_on_uaccess_error && signal) {
tsk->thread.trap_nr = X86_TRAP_PF;
tsk->thread.error_code = error_code | PF_USER;
tsk->thread.cr2 = address;
/* XXX: hwpoison faults will set the wrong code. */
force_sig_info_fault(signal, si_code, address,
tsk, vma, 0);
}
/*
* Barring that, we can do the fixup and be happy.
*/
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);
if (task_stack_end_corrupted(tsk))
printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
tsk->thread.cr2 = address;
tsk->thread.trap_nr = X86_TRAP_PF;
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_DEFAULT "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("%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, struct vm_area_struct *vma,
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;
#ifdef CONFIG_X86_64
/*
* Instruction fetch faults in the vsyscall page might need
* emulation.
*/
if (unlikely((error_code & PF_INSTR) &&
((address & ~0xfff) == VSYSCALL_ADDR))) {
if (emulate_vsyscall(regs, address))
return;
}
#endif
/* Kernel addresses are always protection faults: */
if (address >= TASK_SIZE)
error_code |= PF_PROT;
if (likely(show_unhandled_signals))
show_signal_msg(regs, error_code, address, tsk);
tsk->thread.cr2 = address;
tsk->thread.error_code = error_code;
tsk->thread.trap_nr = X86_TRAP_PF;
force_sig_info_fault(SIGSEGV, si_code, address, tsk, vma, 0);
return;
}
if (is_f00f_bug(regs, address))
return;
no_context(regs, error_code, address, SIGSEGV, si_code);
}
static noinline void
bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct vm_area_struct *vma)
{
__bad_area_nosemaphore(regs, error_code, address, vma, SEGV_MAPERR);
}
static void
__bad_area(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct vm_area_struct *vma, 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, vma, si_code);
}
static noinline void
bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
__bad_area(regs, error_code, address, NULL, SEGV_MAPERR);
}
static inline bool bad_area_access_from_pkeys(unsigned long error_code,
struct vm_area_struct *vma)
{
/* This code is always called on the current mm */
bool foreign = false;
if (!boot_cpu_has(X86_FEATURE_OSPKE))
return false;
if (error_code & PF_PK)
return true;
/* this checks permission keys on the VMA: */
if (!arch_vma_access_permitted(vma, (error_code & PF_WRITE),
(error_code & PF_INSTR), foreign))
return true;
return false;
}
static noinline void
bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct vm_area_struct *vma)
{
/*
* This OSPKE check is not strictly necessary at runtime.
* But, doing it this way allows compiler optimizations
* if pkeys are compiled out.
*/
if (bad_area_access_from_pkeys(error_code, vma))
__bad_area(regs, error_code, address, vma, SEGV_PKUERR);
else
__bad_area(regs, error_code, address, vma, SEGV_ACCERR);
}
static void
do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
struct vm_area_struct *vma, unsigned int fault)
{
struct task_struct *tsk = current;
int code = BUS_ADRERR;
/* Kernel mode? Handle exceptions or die: */
if (!(error_code & PF_USER)) {
no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
return;
}
/* 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_nr = X86_TRAP_PF;
#ifdef CONFIG_MEMORY_FAILURE
if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
printk(KERN_ERR
"MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
tsk->comm, tsk->pid, address);
code = BUS_MCEERR_AR;
}
#endif
force_sig_info_fault(SIGBUS, code, address, tsk, vma, fault);
}
static noinline void
mm_fault_error(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct vm_area_struct *vma,
unsigned int fault)
{
if (fatal_signal_pending(current) && !(error_code & PF_USER)) {
no_context(regs, error_code, address, 0, 0);
return;
}
if (fault & VM_FAULT_OOM) {
/* Kernel mode? Handle exceptions or die: */
if (!(error_code & PF_USER)) {
no_context(regs, error_code, address,
SIGSEGV, SEGV_MAPERR);
return;
}
/*
* 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):
*/
pagefault_out_of_memory();
} else {
if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
VM_FAULT_HWPOISON_LARGE))
do_sigbus(regs, error_code, address, vma, fault);
else if (fault & VM_FAULT_SIGSEGV)
bad_area_nosemaphore(regs, error_code, address, vma);
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;
/*
* Note: We do not do lazy flushing on protection key
* changes, so no spurious fault will ever set PF_PK.
*/
if ((error_code & PF_PK))
return 1;
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.
*
* Spurious faults may only occur if the TLB contains an entry with
* fewer permission than the page table entry. Non-present (P = 0)
* and reserved bit (R = 1) faults are never spurious.
*
* There are no security implications to leaving a stale TLB when
* increasing the permissions on a page.
*
* Returns non-zero if a spurious fault was handled, zero otherwise.
*
* See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3
* (Optional Invalidation).
*/
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;
/*
* Only writes to RO or instruction fetches from NX may cause
* spurious faults.
*
* These could be from user or supervisor accesses but the TLB
* is only lazily flushed after a kernel mapping protection
* change, so user accesses are not expected to cause spurious
* faults.
*/
if (error_code != (PF_WRITE | PF_PROT)
&& error_code != (PF_INSTR | PF_PROT))
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;
}
NOKPROBE_SYMBOL(spurious_fault);
int show_unhandled_signals = 1;
static inline int
access_error(unsigned long error_code, struct vm_area_struct *vma)
{
/* This is only called for the current mm, so: */
bool foreign = false;
/*
* Make sure to check the VMA so that we do not perform
* faults just to hit a PF_PK as soon as we fill in a
* page.
*/
if (!arch_vma_access_permitted(vma, (error_code & PF_WRITE),
(error_code & PF_INSTR), foreign))
return 1;
if (error_code & PF_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;
}
static inline bool smap_violation(int error_code, struct pt_regs *regs)
{
if (!IS_ENABLED(CONFIG_X86_SMAP))
return false;
if (!static_cpu_has(X86_FEATURE_SMAP))
return false;
if (error_code & PF_USER)
return false;
if (!user_mode(regs) && (regs->flags & X86_EFLAGS_AC))
return false;
return true;
}
/*
* This routine handles page faults. It determines the address,
* and the problem, and then passes it off to one of the appropriate
* routines.
*
* This function must have noinline because both callers
* {,trace_}do_page_fault() have notrace on. Having this an actual function
* guarantees there's a function trace entry.
*/
static noinline void
__do_page_fault(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
{
struct vm_area_struct *vma;
struct task_struct *tsk;
struct mm_struct *mm;
int fault, major = 0;
unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
tsk = current;
mm = tsk->mm;
/*
* Detect and handle instructions that would cause a page fault for
* both a tracked kernel page and a userspace page.
*/
if (kmemcheck_active(regs))
kmemcheck_hide(regs);
prefetchw(&mm->mmap_sem);
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))) {
if (vmalloc_fault(address) >= 0)
return;
if (kmemcheck_fault(regs, address, error_code))
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 (kprobes_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, NULL);
return;
}
/* kprobes don't want to hook the spurious faults: */
if (unlikely(kprobes_fault(regs)))
return;
if (unlikely(error_code & PF_RSVD))
pgtable_bad(regs, error_code, address);
if (unlikely(smap_violation(error_code, regs))) {
bad_area_nosemaphore(regs, error_code, address, NULL);
return;
}
/*
* If we're in an interrupt, have no user context or are running
* in a region with pagefaults disabled then we must not take the fault
*/
if (unlikely(faulthandler_disabled() || !mm)) {
bad_area_nosemaphore(regs, error_code, address, NULL);
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(regs)) {
local_irq_enable();
error_code |= PF_USER;
flags |= FAULT_FLAG_USER;
} else {
if (regs->flags & X86_EFLAGS_IF)
local_irq_enable();
}
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
if (error_code & PF_WRITE)
flags |= FAULT_FLAG_WRITE;
if (error_code & PF_INSTR)
flags |= FAULT_FLAG_INSTRUCTION;
/*
* 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, NULL);
return;
}
retry:
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:
if (unlikely(access_error(error_code, vma))) {
bad_area_access_error(regs, error_code, address, vma);
return;
}
/*
* If for any reason at all we couldn't handle the fault,
* make sure we exit gracefully rather than endlessly redo
* the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if
* we get VM_FAULT_RETRY back, the mmap_sem has been unlocked.
*/
fault = handle_mm_fault(mm, vma, address, flags);
major |= fault & VM_FAULT_MAJOR;
/*
* If we need to retry the mmap_sem has already been released,
* and if there is a fatal signal pending there is no guarantee
* that we made any progress. Handle this case first.
*/
if (unlikely(fault & VM_FAULT_RETRY)) {
/* Retry at most once */
if (flags & FAULT_FLAG_ALLOW_RETRY) {
flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
if (!fatal_signal_pending(tsk))
goto retry;
}
/* User mode? Just return to handle the fatal exception */
if (flags & FAULT_FLAG_USER)
return;
/* Not returning to user mode? Handle exceptions or die: */
no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
return;
}
up_read(&mm->mmap_sem);
if (unlikely(fault & VM_FAULT_ERROR)) {
mm_fault_error(regs, error_code, address, vma, fault);
return;
}
/*
* Major/minor page fault accounting. If any of the events
* returned VM_FAULT_MAJOR, we account it as a major fault.
*/
if (major) {
tsk->maj_flt++;
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
} else {
tsk->min_flt++;
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
}
check_v8086_mode(regs, address, tsk);
}
NOKPROBE_SYMBOL(__do_page_fault);
dotraplinkage void notrace
do_page_fault(struct pt_regs *regs, unsigned long error_code)
{
unsigned long address = read_cr2(); /* Get the faulting address */
enum ctx_state prev_state;
/*
* We must have this function tagged with __kprobes, notrace and call
* read_cr2() before calling anything else. To avoid calling any kind
* of tracing machinery before we've observed the CR2 value.
*
* exception_{enter,exit}() contain all sorts of tracepoints.
*/
prev_state = exception_enter();
__do_page_fault(regs, error_code, address);
exception_exit(prev_state);
}
NOKPROBE_SYMBOL(do_page_fault);
#ifdef CONFIG_TRACING
static nokprobe_inline void
trace_page_fault_entries(unsigned long address, struct pt_regs *regs,
unsigned long error_code)
{
if (user_mode(regs))
trace_page_fault_user(address, regs, error_code);
else
trace_page_fault_kernel(address, regs, error_code);
}
dotraplinkage void notrace
trace_do_page_fault(struct pt_regs *regs, unsigned long error_code)
{
/*
* The exception_enter and tracepoint processing could
* trigger another page faults (user space callchain
* reading) and destroy the original cr2 value, so read
* the faulting address now.
*/
unsigned long address = read_cr2();
enum ctx_state prev_state;
prev_state = exception_enter();
trace_page_fault_entries(address, regs, error_code);
__do_page_fault(regs, error_code, address);
exception_exit(prev_state);
}
NOKPROBE_SYMBOL(trace_do_page_fault);
#endif /* CONFIG_TRACING */