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linux-zen-server/arch/x86/mm/fault.c

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// SPDX-License-Identifier: GPL-2.0
/*
* 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/sched/task_stack.h> /* task_stack_*(), ... */
#include <linux/kdebug.h> /* oops_begin/end, ... */
#include <linux/extable.h> /* search_exception_tables */
#include <linux/memblock.h> /* max_low_pfn */
#include <linux/kfence.h> /* kfence_handle_page_fault */
#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 <linux/efi.h> /* efi_crash_gracefully_on_page_fault()*/
#include <linux/mm_types.h>
#include <asm/cpufeature.h> /* boot_cpu_has, ... */
#include <asm/traps.h> /* dotraplinkage, ... */
#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() */
#include <asm/efi.h> /* efi_crash_gracefully_on_page_fault()*/
#include <asm/desc.h> /* store_idt(), ... */
#include <asm/cpu_entry_area.h> /* exception stack */
#include <asm/pgtable_areas.h> /* VMALLOC_START, ... */
#include <asm/kvm_para.h> /* kvm_handle_async_pf */
#include <asm/vdso.h> /* fixup_vdso_exception() */
#include <asm/irq_stack.h>
#define CREATE_TRACE_POINTS
#include <asm/trace/exceptions.h>
/*
* 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;
}
/*
* Prefetch quirks:
*
* 32-bit mode:
*
* Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
* Check that here and ignore it. This is AMD erratum #91.
*
* 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 64-bit mode 0x40..0x4F are valid REX prefixes
*/
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 (get_kernel_nofault(opcode, instr))
return 0;
*prefetch = (instr_lo == 0xF) &&
(opcode == 0x0D || opcode == 0x18);
return 0;
default:
return 0;
}
}
static bool is_amd_k8_pre_npt(void)
{
struct cpuinfo_x86 *c = &boot_cpu_data;
return unlikely(IS_ENABLED(CONFIG_CPU_SUP_AMD) &&
c->x86_vendor == X86_VENDOR_AMD &&
c->x86 == 0xf && c->x86_model < 0x40);
}
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;
/* Erratum #91 affects AMD K8, pre-NPT CPUs */
if (!is_amd_k8_pre_npt())
return 0;
/*
* If it was a exec (instruction fetch) fault on NX page, then
* do not ignore the fault:
*/
if (error_code & X86_PF_INSTR)
return 0;
instr = (void *)convert_ip_to_linear(current, regs);
max_instr = instr + 15;
/*
* This code has historically always bailed out if IP points to a
* not-present page (e.g. due to a race). No one has ever
* complained about this.
*/
pagefault_disable();
while (instr < max_instr) {
unsigned char opcode;
if (user_mode(regs)) {
if (get_user(opcode, (unsigned char __user *) instr))
break;
} else {
if (get_kernel_nofault(opcode, instr))
break;
}
instr++;
if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
break;
}
pagefault_enable();
return prefetch;
}
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;
p4d_t *p4d, *p4d_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_p4d/set_pud.
*/
p4d = p4d_offset(pgd, address);
p4d_k = p4d_offset(pgd_k, address);
if (!p4d_present(*p4d_k))
return NULL;
pud = pud_offset(p4d, address);
pud_k = pud_offset(p4d_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) != pmd_present(*pmd_k))
set_pmd(pmd, *pmd_k);
if (!pmd_present(*pmd_k))
return NULL;
else
BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
return pmd_k;
}
/*
* Handle a fault on the vmalloc or module mapping area
*
* This is needed because there is a race condition between the time
* when the vmalloc mapping code updates the PMD to the point in time
* where it synchronizes this update with the other page-tables in the
* system.
*
* In this race window another thread/CPU can map an area on the same
* PMD, finds it already present and does not synchronize it with the
* rest of the system yet. As a result v[mz]alloc might return areas
* which are not mapped in every page-table in the system, causing an
* unhandled page-fault when they are accessed.
*/
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_pa();
pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
if (!pmd_k)
return -1;
if (pmd_large(*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);
void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
{
unsigned long addr;
for (addr = start & PMD_MASK;
addr >= TASK_SIZE_MAX && addr < VMALLOC_END;
addr += PMD_SIZE) {
struct page *page;
spin_lock(&pgd_lock);
list_for_each_entry(page, &pgd_list, lru) {
spinlock_t *pgt_lock;
/* the pgt_lock only for Xen */
pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
spin_lock(pgt_lock);
vmalloc_sync_one(page_address(page), addr);
spin_unlock(pgt_lock);
}
spin_unlock(&pgd_lock);
}
}
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_pa());
pgd_t *pgd = &base[pgd_index(address)];
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
#ifdef CONFIG_X86_PAE
pr_info("*pdpt = %016Lx ", pgd_val(*pgd));
if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
goto out;
#define pr_pde pr_cont
#else
#define pr_pde pr_info
#endif
p4d = p4d_offset(pgd, address);
pud = pud_offset(p4d, address);
pmd = pmd_offset(pud, address);
pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));
#undef pr_pde
/*
* 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);
pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
out:
pr_cont("\n");
}
#else /* CONFIG_X86_64: */
#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
static int bad_address(void *p)
{
unsigned long dummy;
return get_kernel_nofault(dummy, (unsigned long *)p);
}
static void dump_pagetable(unsigned long address)
{
pgd_t *base = __va(read_cr3_pa());
pgd_t *pgd = base + pgd_index(address);
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
if (bad_address(pgd))
goto bad;
pr_info("PGD %lx ", pgd_val(*pgd));
if (!pgd_present(*pgd))
goto out;
p4d = p4d_offset(pgd, address);
if (bad_address(p4d))
goto bad;
pr_cont("P4D %lx ", p4d_val(*p4d));
if (!p4d_present(*p4d) || p4d_large(*p4d))
goto out;
pud = pud_offset(p4d, address);
if (bad_address(pud))
goto bad;
pr_cont("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;
pr_cont("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;
pr_cont("PTE %lx", pte_val(*pte));
out:
pr_cont("\n");
return;
bad:
pr_info("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 (user_mode(regs))
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;
}
/* Pentium F0 0F C7 C8 bug workaround: */
static int is_f00f_bug(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
{
#ifdef CONFIG_X86_F00F_BUG
if (boot_cpu_has_bug(X86_BUG_F00F) && !(error_code & X86_PF_USER) &&
idt_is_f00f_address(address)) {
handle_invalid_op(regs);
return 1;
}
#endif
return 0;
}
static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index)
{
u32 offset = (index >> 3) * sizeof(struct desc_struct);
unsigned long addr;
struct ldttss_desc desc;
if (index == 0) {
pr_alert("%s: NULL\n", name);
return;
}
if (offset + sizeof(struct ldttss_desc) >= gdt->size) {
pr_alert("%s: 0x%hx -- out of bounds\n", name, index);
return;
}
if (copy_from_kernel_nofault(&desc, (void *)(gdt->address + offset),
sizeof(struct ldttss_desc))) {
pr_alert("%s: 0x%hx -- GDT entry is not readable\n",
name, index);
return;
}
addr = desc.base0 | (desc.base1 << 16) | ((unsigned long)desc.base2 << 24);
#ifdef CONFIG_X86_64
addr |= ((u64)desc.base3 << 32);
#endif
pr_alert("%s: 0x%hx -- base=0x%lx limit=0x%x\n",
name, index, addr, (desc.limit0 | (desc.limit1 << 16)));
}
static void
show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
if (!oops_may_print())
return;
if (error_code & X86_PF_INSTR) {
unsigned int level;
pgd_t *pgd;
pte_t *pte;
pgd = __va(read_cr3_pa());
pgd += pgd_index(address);
pte = lookup_address_in_pgd(pgd, address, &level);
if (pte && pte_present(*pte) && !pte_exec(*pte))
pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n",
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))
pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n",
from_kuid(&init_user_ns, current_uid()));
}
if (address < PAGE_SIZE && !user_mode(regs))
pr_alert("BUG: kernel NULL pointer dereference, address: %px\n",
(void *)address);
else
pr_alert("BUG: unable to handle page fault for address: %px\n",
(void *)address);
pr_alert("#PF: %s %s in %s mode\n",
(error_code & X86_PF_USER) ? "user" : "supervisor",
(error_code & X86_PF_INSTR) ? "instruction fetch" :
(error_code & X86_PF_WRITE) ? "write access" :
"read access",
user_mode(regs) ? "user" : "kernel");
pr_alert("#PF: error_code(0x%04lx) - %s\n", error_code,
!(error_code & X86_PF_PROT) ? "not-present page" :
(error_code & X86_PF_RSVD) ? "reserved bit violation" :
(error_code & X86_PF_PK) ? "protection keys violation" :
"permissions violation");
if (!(error_code & X86_PF_USER) && user_mode(regs)) {
struct desc_ptr idt, gdt;
u16 ldtr, tr;
/*
* This can happen for quite a few reasons. The more obvious
* ones are faults accessing the GDT, or LDT. Perhaps
* surprisingly, if the CPU tries to deliver a benign or
* contributory exception from user code and gets a page fault
* during delivery, the page fault can be delivered as though
* it originated directly from user code. This could happen
* due to wrong permissions on the IDT, GDT, LDT, TSS, or
* kernel or IST stack.
*/
store_idt(&idt);
/* Usable even on Xen PV -- it's just slow. */
native_store_gdt(&gdt);
pr_alert("IDT: 0x%lx (limit=0x%hx) GDT: 0x%lx (limit=0x%hx)\n",
idt.address, idt.size, gdt.address, gdt.size);
store_ldt(ldtr);
show_ldttss(&gdt, "LDTR", ldtr);
store_tr(tr);
show_ldttss(&gdt, "TR", tr);
}
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);
if (__die("Bad pagetable", regs, error_code))
sig = 0;
oops_end(flags, regs, sig);
}
static void sanitize_error_code(unsigned long address,
unsigned long *error_code)
{
/*
* To avoid leaking information about the kernel page
* table layout, pretend that user-mode accesses to
* kernel addresses are always protection faults.
*
* NB: This means that failed vsyscalls with vsyscall=none
* will have the PROT bit. This doesn't leak any
* information and does not appear to cause any problems.
*/
if (address >= TASK_SIZE_MAX)
*error_code |= X86_PF_PROT;
}
static void set_signal_archinfo(unsigned long address,
unsigned long error_code)
{
struct task_struct *tsk = current;
tsk->thread.trap_nr = X86_TRAP_PF;
tsk->thread.error_code = error_code | X86_PF_USER;
tsk->thread.cr2 = address;
}
static noinline void
page_fault_oops(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
{
#ifdef CONFIG_VMAP_STACK
struct stack_info info;
#endif
unsigned long flags;
int sig;
if (user_mode(regs)) {
/*
* Implicit kernel access from user mode? Skip the stack
* overflow and EFI special cases.
*/
goto oops;
}
#ifdef CONFIG_VMAP_STACK
/*
* Stack overflow? During boot, we can fault near the initial
* stack in the direct map, but that's not an overflow -- check
* that we're in vmalloc space to avoid this.
*/
if (is_vmalloc_addr((void *)address) &&
get_stack_guard_info((void *)address, &info)) {
/*
* We're likely to be running with very little stack space
* left. It's plausible that we'd hit this condition but
* double-fault even before we get this far, in which case
* we're fine: the double-fault handler will deal with it.
*
* We don't want to make it all the way into the oops code
* and then double-fault, though, because we're likely to
* break the console driver and lose most of the stack dump.
*/
call_on_stack(__this_cpu_ist_top_va(DF) - sizeof(void*),
handle_stack_overflow,
ASM_CALL_ARG3,
, [arg1] "r" (regs), [arg2] "r" (address), [arg3] "r" (&info));
unreachable();
}
#endif
/*
* Buggy firmware could access regions which might page fault. If
* this happens, EFI has a special OOPS path that will try to
* avoid hanging the system.
*/
if (IS_ENABLED(CONFIG_EFI))
efi_crash_gracefully_on_page_fault(address);
/* Only not-present faults should be handled by KFENCE. */
if (!(error_code & X86_PF_PROT) &&
kfence_handle_page_fault(address, error_code & X86_PF_WRITE, regs))
return;
oops:
/*
* 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(current))
printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
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);
}
static noinline void
kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code,
unsigned long address, int signal, int si_code,
u32 pkey)
{
WARN_ON_ONCE(user_mode(regs));
/* Are we prepared to handle this kernel fault? */
if (fixup_exception(regs, X86_TRAP_PF, error_code, address)) {
/*
* 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.sig_on_uaccess_err && signal) {
sanitize_error_code(address, &error_code);
set_signal_archinfo(address, error_code);
if (si_code == SEGV_PKUERR) {
force_sig_pkuerr((void __user *)address, pkey);
} else {
/* XXX: hwpoison faults will set the wrong code. */
force_sig_fault(signal, si_code, (void __user *)address);
}
}
/*
* Barring that, we can do the fixup and be happy.
*/
return;
}
/*
* AMD erratum #91 manifests as a spurious page fault on a PREFETCH
* instruction.
*/
if (is_prefetch(regs, error_code, address))
return;
page_fault_oops(regs, error_code, address);
}
/*
* 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)
{
const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;
/* This is a racy snapshot, but it's better than nothing. */
int cpu = raw_smp_processor_id();
if (!unhandled_signal(tsk, SIGSEGV))
return;
if (!printk_ratelimit())
return;
printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx",
loglvl, tsk->comm, task_pid_nr(tsk), address,
(void *)regs->ip, (void *)regs->sp, error_code);
print_vma_addr(KERN_CONT " in ", regs->ip);
/*
* Dump the likely CPU where the fatal segfault happened.
* This can help identify faulty hardware.
*/
printk(KERN_CONT " likely on CPU %d (core %d, socket %d)", cpu,
topology_core_id(cpu), topology_physical_package_id(cpu));
printk(KERN_CONT "\n");
show_opcodes(regs, loglvl);
}
/*
* The (legacy) vsyscall page is the long page in the kernel portion
* of the address space that has user-accessible permissions.
*/
static bool is_vsyscall_vaddr(unsigned long vaddr)
{
return unlikely((vaddr & PAGE_MASK) == VSYSCALL_ADDR);
}
static void
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
unsigned long address, u32 pkey, int si_code)
{
struct task_struct *tsk = current;
if (!user_mode(regs)) {
kernelmode_fixup_or_oops(regs, error_code, address,
SIGSEGV, si_code, pkey);
return;
}
if (!(error_code & X86_PF_USER)) {
/* Implicit user access to kernel memory -- just oops */
page_fault_oops(regs, error_code, address);
return;
}
/*
* User mode accesses just cause a SIGSEGV.
* 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;
sanitize_error_code(address, &error_code);
if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
return;
if (likely(show_unhandled_signals))
show_signal_msg(regs, error_code, address, tsk);
set_signal_archinfo(address, error_code);
if (si_code == SEGV_PKUERR)
force_sig_pkuerr((void __user *)address, pkey);
else
force_sig_fault(SIGSEGV, si_code, (void __user *)address);
local_irq_disable();
}
static noinline void
bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
{
__bad_area_nosemaphore(regs, error_code, address, 0, SEGV_MAPERR);
}
static void
__bad_area(struct pt_regs *regs, unsigned long error_code,
unsigned long address, u32 pkey, 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..
*/
mmap_read_unlock(mm);
__bad_area_nosemaphore(regs, error_code, address, pkey, si_code);
}
static noinline void
bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
__bad_area(regs, error_code, address, 0, 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 (!cpu_feature_enabled(X86_FEATURE_OSPKE))
return false;
if (error_code & X86_PF_PK)
return true;
/* this checks permission keys on the VMA: */
if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
(error_code & X86_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)) {
/*
* 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. This function captures the pkey from
* the vma and passes it to userspace so userspace can discover
* which protection key was set on the PTE.
*
* If we get here, we know that the hardware signaled a X86_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_lock, etc...
* 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
* faulted on a pte with its pkey=4.
*/
u32 pkey = vma_pkey(vma);
__bad_area(regs, error_code, address, pkey, SEGV_PKUERR);
} else {
__bad_area(regs, error_code, address, 0, SEGV_ACCERR);
}
}
static void
do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
vm_fault_t fault)
{
/* Kernel mode? Handle exceptions or die: */
if (!user_mode(regs)) {
kernelmode_fixup_or_oops(regs, error_code, address,
SIGBUS, BUS_ADRERR, ARCH_DEFAULT_PKEY);
return;
}
/* User-space => ok to do another page fault: */
if (is_prefetch(regs, error_code, address))
return;
sanitize_error_code(address, &error_code);
if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
return;
set_signal_archinfo(address, error_code);
#ifdef CONFIG_MEMORY_FAILURE
if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
struct task_struct *tsk = current;
unsigned lsb = 0;
pr_err(
"MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
tsk->comm, tsk->pid, 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;
force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
return;
}
#endif
force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
}
static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte)
{
if ((error_code & X86_PF_WRITE) && !pte_write(*pte))
return 0;
if ((error_code & X86_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.
*
* 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_kernel_fault(unsigned long error_code, unsigned long address)
{
pgd_t *pgd;
p4d_t *p4d;
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 != (X86_PF_WRITE | X86_PF_PROT) &&
error_code != (X86_PF_INSTR | X86_PF_PROT))
return 0;
pgd = init_mm.pgd + pgd_index(address);
if (!pgd_present(*pgd))
return 0;
p4d = p4d_offset(pgd, address);
if (!p4d_present(*p4d))
return 0;
if (p4d_large(*p4d))
return spurious_kernel_fault_check(error_code, (pte_t *) p4d);
pud = pud_offset(p4d, address);
if (!pud_present(*pud))
return 0;
if (pud_large(*pud))
return spurious_kernel_fault_check(error_code, (pte_t *) pud);
pmd = pmd_offset(pud, address);
if (!pmd_present(*pmd))
return 0;
if (pmd_large(*pmd))
return spurious_kernel_fault_check(error_code, (pte_t *) pmd);
pte = pte_offset_kernel(pmd, address);
if (!pte_present(*pte))
return 0;
ret = spurious_kernel_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_kernel_fault_check(error_code, (pte_t *) pmd);
WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
return ret;
}
NOKPROBE_SYMBOL(spurious_kernel_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;
/*
* Read or write was blocked by protection keys. This is
* always an unconditional error and can never result in
* a follow-up action to resolve the fault, like a COW.
*/
if (error_code & X86_PF_PK)
return 1;
/*
* SGX hardware blocked the access. This usually happens
* when the enclave memory contents have been destroyed, like
* after a suspend/resume cycle. In any case, the kernel can't
* fix the cause of the fault. Handle the fault as an access
* error even in cases where no actual access violation
* occurred. This allows userspace to rebuild the enclave in
* response to the signal.
*/
if (unlikely(error_code & X86_PF_SGX))
return 1;
/*
* Make sure to check the VMA so that we do not perform
* faults just to hit a X86_PF_PK as soon as we fill in a
* page.
*/
if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
(error_code & X86_PF_INSTR), foreign))
return 1;
if (error_code & X86_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 & X86_PF_PROT))
return 1;
/* read, not present: */
if (unlikely(!vma_is_accessible(vma)))
return 1;
return 0;
}
bool fault_in_kernel_space(unsigned long address)
{
/*
* On 64-bit systems, the vsyscall page is at an address above
* TASK_SIZE_MAX, but is not considered part of the kernel
* address space.
*/
if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address))
return false;
return address >= TASK_SIZE_MAX;
}
/*
* Called for all faults where 'address' is part of the kernel address
* space. Might get called for faults that originate from *code* that
* ran in userspace or the kernel.
*/
static void
do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
unsigned long address)
{
/*
* Protection keys exceptions only happen on user pages. We
* have no user pages in the kernel portion of the address
* space, so do not expect them here.
*/
WARN_ON_ONCE(hw_error_code & X86_PF_PK);
#ifdef CONFIG_X86_32
/*
* We can 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.
*
* Before doing this on-demand faulting, ensure that the
* fault is not any of the following:
* 1. A fault on a PTE with a reserved bit set.
* 2. A fault caused by a user-mode access. (Do not demand-
* fault kernel memory due to user-mode accesses).
* 3. A fault caused by a page-level protection violation.
* (A demand fault would be on a non-present page which
* would have X86_PF_PROT==0).
*
* This is only needed to close a race condition on x86-32 in
* the vmalloc mapping/unmapping code. See the comment above
* vmalloc_fault() for details. On x86-64 the race does not
* exist as the vmalloc mappings don't need to be synchronized
* there.
*/
if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
if (vmalloc_fault(address) >= 0)
return;
}
#endif
if (is_f00f_bug(regs, hw_error_code, address))
return;
/* Was the fault spurious, caused by lazy TLB invalidation? */
if (spurious_kernel_fault(hw_error_code, address))
return;
/* kprobes don't want to hook the spurious faults: */
if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF)))
return;
/*
* Note, despite being a "bad area", there are quite a few
* acceptable reasons to get here, such as erratum fixups
* and handling kernel code that can fault, like get_user().
*
* Don't take the mm semaphore here. If we fixup a prefetch
* fault we could otherwise deadlock:
*/
bad_area_nosemaphore(regs, hw_error_code, address);
}
NOKPROBE_SYMBOL(do_kern_addr_fault);
/*
* Handle faults in the user portion of the address space. Nothing in here
* should check X86_PF_USER without a specific justification: for almost
* all purposes, we should treat a normal kernel access to user memory
* (e.g. get_user(), put_user(), etc.) the same as the WRUSS instruction.
* The one exception is AC flag handling, which is, per the x86
* architecture, special for WRUSS.
*/
static inline
void do_user_addr_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;
vm_fault_t fault;
unsigned int flags = FAULT_FLAG_DEFAULT;
tsk = current;
mm = tsk->mm;
if (unlikely((error_code & (X86_PF_USER | X86_PF_INSTR)) == X86_PF_INSTR)) {
/*
* Whoops, this is kernel mode code trying to execute from
* user memory. Unless this is AMD erratum #93, which
* corrupts RIP such that it looks like a user address,
* this is unrecoverable. Don't even try to look up the
* VMA or look for extable entries.
*/
if (is_errata93(regs, address))
return;
page_fault_oops(regs, error_code, address);
return;
}
/* kprobes don't want to hook the spurious faults: */
if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF)))
return;
/*
* Reserved bits are never expected to be set on
* entries in the user portion of the page tables.
*/
if (unlikely(error_code & X86_PF_RSVD))
pgtable_bad(regs, error_code, address);
/*
* If SMAP is on, check for invalid kernel (supervisor) access to user
* pages in the user address space. The odd case here is WRUSS,
* which, according to the preliminary documentation, does not respect
* SMAP and will have the USER bit set so, in all cases, SMAP
* enforcement appears to be consistent with the USER bit.
*/
if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) &&
!(error_code & X86_PF_USER) &&
!(regs->flags & X86_EFLAGS_AC))) {
/*
* No extable entry here. This was a kernel access to an
* invalid pointer. get_kernel_nofault() will not get here.
*/
page_fault_oops(regs, error_code, address);
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);
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();
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 & X86_PF_WRITE)
flags |= FAULT_FLAG_WRITE;
if (error_code & X86_PF_INSTR)
flags |= FAULT_FLAG_INSTRUCTION;
#ifdef CONFIG_X86_64
/*
* Faults in the vsyscall page might need emulation. The
* vsyscall page is at a high address (>PAGE_OFFSET), but is
* considered to be part of the user address space.
*
* The vsyscall page does not have a "real" VMA, so do this
* emulation before we go searching for VMAs.
*
* PKRU never rejects instruction fetches, so we don't need
* to consider the PF_PK bit.
*/
if (is_vsyscall_vaddr(address)) {
if (emulate_vsyscall(error_code, regs, address))
return;
}
#endif
/*
* Kernel-mode access to the user address space should only occur
* on well-defined single instructions listed in the exception
* tables. But, an erroneous kernel fault occurring outside one of
* those areas which also holds mmap_lock might deadlock attempting
* to validate the fault against the address space.
*
* Only do the expensive exception table search when we might be at
* risk of a deadlock. This happens if we
* 1. Failed to acquire mmap_lock, and
* 2. The access did not originate in userspace.
*/
if (unlikely(!mmap_read_trylock(mm))) {
if (!user_mode(regs) && !search_exception_tables(regs->ip)) {
/*
* Fault from code in kernel from
* which we do not expect faults.
*/
bad_area_nosemaphore(regs, error_code, address);
return;
}
retry:
mmap_read_lock(mm);
} 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 (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_lock has been unlocked.
*
* Note that handle_userfault() may also release and reacquire mmap_lock
* (and not return with VM_FAULT_RETRY), when returning to userland to
* repeat the page fault later with a VM_FAULT_NOPAGE retval
* (potentially after handling any pending signal during the return to
* userland). The return to userland is identified whenever
* FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags.
*/
fault = handle_mm_fault(vma, address, flags, regs);
if (fault_signal_pending(fault, regs)) {
/*
* Quick path to respond to signals. The core mm code
* has unlocked the mm for us if we get here.
*/
if (!user_mode(regs))
kernelmode_fixup_or_oops(regs, error_code, address,
SIGBUS, BUS_ADRERR,
ARCH_DEFAULT_PKEY);
return;
}
/* The fault is fully completed (including releasing mmap lock) */
if (fault & VM_FAULT_COMPLETED)
return;
/*
* If we need to retry the mmap_lock 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)) {
flags |= FAULT_FLAG_TRIED;
goto retry;
}
mmap_read_unlock(mm);
if (likely(!(fault & VM_FAULT_ERROR)))
return;
if (fatal_signal_pending(current) && !user_mode(regs)) {
kernelmode_fixup_or_oops(regs, error_code, address,
0, 0, ARCH_DEFAULT_PKEY);
return;
}
if (fault & VM_FAULT_OOM) {
/* Kernel mode? Handle exceptions or die: */
if (!user_mode(regs)) {
kernelmode_fixup_or_oops(regs, error_code, address,
SIGSEGV, SEGV_MAPERR,
ARCH_DEFAULT_PKEY);
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, fault);
else if (fault & VM_FAULT_SIGSEGV)
bad_area_nosemaphore(regs, error_code, address);
else
BUG();
}
}
NOKPROBE_SYMBOL(do_user_addr_fault);
static __always_inline void
trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
{
if (!trace_pagefault_enabled())
return;
if (user_mode(regs))
trace_page_fault_user(address, regs, error_code);
else
trace_page_fault_kernel(address, regs, error_code);
}
static __always_inline void
handle_page_fault(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
{
trace_page_fault_entries(regs, error_code, address);
if (unlikely(kmmio_fault(regs, address)))
return;
/* Was the fault on kernel-controlled part of the address space? */
if (unlikely(fault_in_kernel_space(address))) {
do_kern_addr_fault(regs, error_code, address);
} else {
do_user_addr_fault(regs, error_code, address);
/*
* User address page fault handling might have reenabled
* interrupts. Fixing up all potential exit points of
* do_user_addr_fault() and its leaf functions is just not
* doable w/o creating an unholy mess or turning the code
* upside down.
*/
local_irq_disable();
}
}
DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
{
unsigned long address = read_cr2();
irqentry_state_t state;
prefetchw(&current->mm->mmap_lock);
/*
* KVM uses #PF vector to deliver 'page not present' events to guests
* (asynchronous page fault mechanism). The event happens when a
* userspace task is trying to access some valid (from guest's point of
* view) memory which is not currently mapped by the host (e.g. the
* memory is swapped out). Note, the corresponding "page ready" event
* which is injected when the memory becomes available, is delivered via
* an interrupt mechanism and not a #PF exception
* (see arch/x86/kernel/kvm.c: sysvec_kvm_asyncpf_interrupt()).
*
* We are relying on the interrupted context being sane (valid RSP,
* relevant locks not held, etc.), which is fine as long as the
* interrupted context had IF=1. We are also relying on the KVM
* async pf type field and CR2 being read consistently instead of
* getting values from real and async page faults mixed up.
*
* Fingers crossed.
*
* The async #PF handling code takes care of idtentry handling
* itself.
*/
if (kvm_handle_async_pf(regs, (u32)address))
return;
/*
* Entry handling for valid #PF from kernel mode is slightly
* different: RCU is already watching and ct_irq_enter() must not
* be invoked because a kernel fault on a user space address might
* sleep.
*
* In case the fault hit a RCU idle region the conditional entry
* code reenabled RCU to avoid subsequent wreckage which helps
* debuggability.
*/
state = irqentry_enter(regs);
instrumentation_begin();
handle_page_fault(regs, error_code, address);
instrumentation_end();
irqentry_exit(regs, state);
}
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