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serenity/Kernel/Memory/Region.cpp
Andreas Kling 0a83c03546 Kernel: Don't unregister Region from RegionTree *before* unmapping it 
If we unregister from the RegionTree before unmapping, there's a race
where a new region can get inserted at the same address that we're about
to unmap. If this happens, ~Region() will then unmap the newly inserted
region, which now finds itself with cleared-out page table entries.
2022-04-05 13:46:50 +02:00

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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Memory.h>
#include <AK/StringView.h>
#include <Kernel/Arch/PageDirectory.h>
#include <Kernel/Arch/PageFault.h>
#include <Kernel/Debug.h>
#include <Kernel/FileSystem/Inode.h>
#include <Kernel/Memory/AnonymousVMObject.h>
#include <Kernel/Memory/MemoryManager.h>
#include <Kernel/Memory/PageDirectory.h>
#include <Kernel/Memory/Region.h>
#include <Kernel/Memory/SharedInodeVMObject.h>
#include <Kernel/Panic.h>
#include <Kernel/Process.h>
#include <Kernel/Scheduler.h>
#include <Kernel/Thread.h>
namespace Kernel::Memory {
Region::Region()
: m_range(VirtualRange({}, 0))
{
}
Region::Region(NonnullRefPtr<VMObject> vmobject, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable cacheable, bool shared)
: m_range(VirtualRange({}, 0))
, m_offset_in_vmobject(offset_in_vmobject)
, m_vmobject(move(vmobject))
, m_name(move(name))
, m_access(access | ((access & 0x7) << 4))
, m_shared(shared)
, m_cacheable(cacheable == Cacheable::Yes)
{
m_vmobject->add_region(*this);
}
Region::Region(VirtualRange const& range, NonnullRefPtr<VMObject> vmobject, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable cacheable, bool shared)
: m_range(range)
, m_offset_in_vmobject(offset_in_vmobject)
, m_vmobject(move(vmobject))
, m_name(move(name))
, m_access(access | ((access & 0x7) << 4))
, m_shared(shared)
, m_cacheable(cacheable == Cacheable::Yes)
{
VERIFY(m_range.base().is_page_aligned());
VERIFY(m_range.size());
VERIFY((m_range.size() % PAGE_SIZE) == 0);
m_vmobject->add_region(*this);
}
Region::~Region()
{
if (is_writable() && vmobject().is_shared_inode()) {
// FIXME: This is very aggressive. Find a way to do less work!
(void)static_cast<SharedInodeVMObject&>(vmobject()).sync();
}
m_vmobject->remove_region(*this);
if (m_page_directory) {
SpinlockLocker pd_locker(m_page_directory->get_lock());
if (!is_readable() && !is_writable() && !is_executable()) {
// If the region is "PROT_NONE", we didn't map it in the first place.
} else {
SpinlockLocker mm_locker(s_mm_lock);
unmap_with_locks_held(ShouldFlushTLB::Yes, pd_locker, mm_locker);
VERIFY(!m_page_directory);
}
}
if (is_kernel())
MM.unregister_kernel_region(*this);
}
ErrorOr<NonnullOwnPtr<Region>> Region::create_unbacked()
{
return adopt_nonnull_own_or_enomem(new (nothrow) Region);
}
ErrorOr<NonnullOwnPtr<Region>> Region::create_unplaced(NonnullRefPtr<VMObject> vmobject, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable cacheable, bool shared)
{
return adopt_nonnull_own_or_enomem(new (nothrow) Region(move(vmobject), offset_in_vmobject, move(name), access, cacheable, shared));
}
ErrorOr<NonnullOwnPtr<Region>> Region::try_clone()
{
VERIFY(Process::has_current());
if (m_shared) {
VERIFY(!m_stack);
if (vmobject().is_inode())
VERIFY(vmobject().is_shared_inode());
// Create a new region backed by the same VMObject.
OwnPtr<KString> region_name;
if (m_name)
region_name = TRY(m_name->try_clone());
auto region = TRY(Region::try_create_user_accessible(
m_range, vmobject(), m_offset_in_vmobject, move(region_name), access(), m_cacheable ? Cacheable::Yes : Cacheable::No, m_shared));
region->set_mmap(m_mmap);
region->set_shared(m_shared);
region->set_syscall_region(is_syscall_region());
return region;
}
if (vmobject().is_inode())
VERIFY(vmobject().is_private_inode());
auto vmobject_clone = TRY(vmobject().try_clone());
// Set up a COW region. The parent (this) region becomes COW as well!
if (is_writable())
remap();
OwnPtr<KString> clone_region_name;
if (m_name)
clone_region_name = TRY(m_name->try_clone());
auto clone_region = TRY(Region::try_create_user_accessible(
m_range, move(vmobject_clone), m_offset_in_vmobject, move(clone_region_name), access(), m_cacheable ? Cacheable::Yes : Cacheable::No, m_shared));
if (m_stack) {
VERIFY(is_readable());
VERIFY(is_writable());
VERIFY(vmobject().is_anonymous());
clone_region->set_stack(true);
}
clone_region->set_syscall_region(is_syscall_region());
clone_region->set_mmap(m_mmap);
return clone_region;
}
void Region::set_vmobject(NonnullRefPtr<VMObject>&& obj)
{
if (m_vmobject.ptr() == obj.ptr())
return;
m_vmobject->remove_region(*this);
m_vmobject = move(obj);
m_vmobject->add_region(*this);
}
size_t Region::cow_pages() const
{
if (!vmobject().is_anonymous())
return 0;
return static_cast<AnonymousVMObject const&>(vmobject()).cow_pages();
}
size_t Region::amount_dirty() const
{
if (!vmobject().is_inode())
return amount_resident();
return static_cast<InodeVMObject const&>(vmobject()).amount_dirty();
}
size_t Region::amount_resident() const
{
size_t bytes = 0;
for (size_t i = 0; i < page_count(); ++i) {
auto const* page = physical_page(i);
if (page && !page->is_shared_zero_page() && !page->is_lazy_committed_page())
bytes += PAGE_SIZE;
}
return bytes;
}
size_t Region::amount_shared() const
{
size_t bytes = 0;
for (size_t i = 0; i < page_count(); ++i) {
auto const* page = physical_page(i);
if (page && page->ref_count() > 1 && !page->is_shared_zero_page() && !page->is_lazy_committed_page())
bytes += PAGE_SIZE;
}
return bytes;
}
ErrorOr<NonnullOwnPtr<Region>> Region::try_create_user_accessible(VirtualRange const& range, NonnullRefPtr<VMObject> vmobject, size_t offset_in_vmobject, OwnPtr<KString> name, Region::Access access, Cacheable cacheable, bool shared)
{
return adopt_nonnull_own_or_enomem(new (nothrow) Region(range, move(vmobject), offset_in_vmobject, move(name), access, cacheable, shared));
}
bool Region::should_cow(size_t page_index) const
{
if (!vmobject().is_anonymous())
return false;
return static_cast<AnonymousVMObject const&>(vmobject()).should_cow(first_page_index() + page_index, m_shared);
}
ErrorOr<void> Region::set_should_cow(size_t page_index, bool cow)
{
VERIFY(!m_shared);
if (vmobject().is_anonymous())
TRY(static_cast<AnonymousVMObject&>(vmobject()).set_should_cow(first_page_index() + page_index, cow));
return {};
}
bool Region::map_individual_page_impl(size_t page_index)
{
VERIFY(m_page_directory->get_lock().is_locked_by_current_processor());
VERIFY(s_mm_lock.is_locked_by_current_processor());
auto page_vaddr = vaddr_from_page_index(page_index);
bool user_allowed = page_vaddr.get() >= USER_RANGE_BASE && is_user_address(page_vaddr);
if (is_mmap() && !user_allowed) {
PANIC("About to map mmap'ed page at a kernel address");
}
auto* pte = MM.ensure_pte(*m_page_directory, page_vaddr);
if (!pte)
return false;
auto* page = physical_page(page_index);
if (!page || (!is_readable() && !is_writable())) {
pte->clear();
} else {
pte->set_cache_disabled(!m_cacheable);
pte->set_physical_page_base(page->paddr().get());
pte->set_present(true);
if (page->is_shared_zero_page() || page->is_lazy_committed_page() || should_cow(page_index))
pte->set_writable(false);
else
pte->set_writable(is_writable());
if (Processor::current().has_nx())
pte->set_execute_disabled(!is_executable());
if (Processor::current().has_pat())
pte->set_pat(is_write_combine());
pte->set_user_allowed(user_allowed);
}
return true;
}
bool Region::do_remap_vmobject_page(size_t page_index, bool with_flush)
{
if (!m_page_directory)
return true; // not an error, region may have not yet mapped it
if (!translate_vmobject_page(page_index))
return true; // not an error, region doesn't map this page
SpinlockLocker page_lock(m_page_directory->get_lock());
SpinlockLocker lock(s_mm_lock);
VERIFY(physical_page(page_index));
bool success = map_individual_page_impl(page_index);
if (with_flush)
MemoryManager::flush_tlb(m_page_directory, vaddr_from_page_index(page_index));
return success;
}
bool Region::remap_vmobject_page(size_t page_index, bool with_flush)
{
auto& vmobject = this->vmobject();
bool success = true;
SpinlockLocker lock(vmobject.m_lock);
vmobject.for_each_region([&](auto& region) {
if (!region.do_remap_vmobject_page(page_index, with_flush))
success = false;
});
return success;
}
void Region::unmap(ShouldFlushTLB should_flush_tlb)
{
if (!m_page_directory)
return;
SpinlockLocker pd_locker(m_page_directory->get_lock());
SpinlockLocker mm_locker(s_mm_lock);
unmap_with_locks_held(should_flush_tlb, pd_locker, mm_locker);
}
void Region::unmap_with_locks_held(ShouldFlushTLB should_flush_tlb, SpinlockLocker<RecursiveSpinlock>&, SpinlockLocker<RecursiveSpinlock>&)
{
if (!m_page_directory)
return;
size_t count = page_count();
for (size_t i = 0; i < count; ++i) {
auto vaddr = vaddr_from_page_index(i);
MM.release_pte(*m_page_directory, vaddr, i == count - 1 ? MemoryManager::IsLastPTERelease::Yes : MemoryManager::IsLastPTERelease::No);
}
if (should_flush_tlb == ShouldFlushTLB::Yes)
MemoryManager::flush_tlb(m_page_directory, vaddr(), page_count());
m_page_directory = nullptr;
}
void Region::set_page_directory(PageDirectory& page_directory)
{
VERIFY(!m_page_directory || m_page_directory == &page_directory);
VERIFY(s_mm_lock.is_locked_by_current_processor());
m_page_directory = page_directory;
}
ErrorOr<void> Region::map(PageDirectory& page_directory, ShouldFlushTLB should_flush_tlb)
{
SpinlockLocker page_lock(page_directory.get_lock());
SpinlockLocker lock(s_mm_lock);
// FIXME: Find a better place for this sanity check(?)
if (is_user() && !is_shared()) {
VERIFY(!vmobject().is_shared_inode());
}
set_page_directory(page_directory);
size_t page_index = 0;
while (page_index < page_count()) {
if (!map_individual_page_impl(page_index))
break;
++page_index;
}
if (page_index > 0) {
if (should_flush_tlb == ShouldFlushTLB::Yes)
MemoryManager::flush_tlb(m_page_directory, vaddr(), page_index);
if (page_index == page_count())
return {};
}
return ENOMEM;
}
void Region::remap()
{
VERIFY(m_page_directory);
auto result = map(*m_page_directory);
if (result.is_error())
TODO();
}
ErrorOr<void> Region::set_write_combine(bool enable)
{
if (enable && !Processor::current().has_pat()) {
dbgln("PAT is not supported, implement MTRR fallback if available");
return Error::from_errno(ENOTSUP);
}
m_write_combine = enable;
remap();
return {};
}
void Region::clear_to_zero()
{
VERIFY(vmobject().is_anonymous());
SpinlockLocker locker(vmobject().m_lock);
for (auto i = 0u; i < page_count(); ++i) {
auto& page = physical_page_slot(i);
VERIFY(page);
if (page->is_shared_zero_page())
continue;
page = MM.shared_zero_page();
}
}
PageFaultResponse Region::handle_fault(PageFault const& fault)
{
auto page_index_in_region = page_index_from_address(fault.vaddr());
if (fault.type() == PageFault::Type::PageNotPresent) {
if (fault.is_read() && !is_readable()) {
dbgln("NP(non-readable) fault in Region({})[{}]", this, page_index_in_region);
return PageFaultResponse::ShouldCrash;
}
if (fault.is_write() && !is_writable()) {
dbgln("NP(non-writable) write fault in Region({})[{}] at {}", this, page_index_in_region, fault.vaddr());
return PageFaultResponse::ShouldCrash;
}
if (vmobject().is_inode()) {
dbgln_if(PAGE_FAULT_DEBUG, "NP(inode) fault in Region({})[{}]", this, page_index_in_region);
return handle_inode_fault(page_index_in_region);
}
auto& page_slot = physical_page_slot(page_index_in_region);
if (page_slot->is_lazy_committed_page()) {
auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
VERIFY(m_vmobject->is_anonymous());
page_slot = static_cast<AnonymousVMObject&>(*m_vmobject).allocate_committed_page({});
if (!remap_vmobject_page(page_index_in_vmobject))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
dbgln("BUG! Unexpected NP fault at {}", fault.vaddr());
dbgln(" - Physical page slot pointer: {:p}", page_slot.ptr());
if (page_slot) {
dbgln(" - Physical page: {}", page_slot->paddr());
dbgln(" - Lazy committed: {}", page_slot->is_lazy_committed_page());
dbgln(" - Shared zero: {}", page_slot->is_shared_zero_page());
}
return PageFaultResponse::ShouldCrash;
}
VERIFY(fault.type() == PageFault::Type::ProtectionViolation);
if (fault.access() == PageFault::Access::Write && is_writable() && should_cow(page_index_in_region)) {
dbgln_if(PAGE_FAULT_DEBUG, "PV(cow) fault in Region({})[{}] at {}", this, page_index_in_region, fault.vaddr());
auto* phys_page = physical_page(page_index_in_region);
if (phys_page->is_shared_zero_page() || phys_page->is_lazy_committed_page()) {
dbgln_if(PAGE_FAULT_DEBUG, "NP(zero) fault in Region({})[{}] at {}", this, page_index_in_region, fault.vaddr());
return handle_zero_fault(page_index_in_region);
}
return handle_cow_fault(page_index_in_region);
}
dbgln("PV(error) fault in Region({})[{}] at {}", this, page_index_in_region, fault.vaddr());
return PageFaultResponse::ShouldCrash;
}
PageFaultResponse Region::handle_zero_fault(size_t page_index_in_region)
{
VERIFY_INTERRUPTS_DISABLED();
VERIFY(vmobject().is_anonymous());
auto& page_slot = physical_page_slot(page_index_in_region);
auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
SpinlockLocker locker(vmobject().m_lock);
if (!page_slot.is_null() && !page_slot->is_shared_zero_page() && !page_slot->is_lazy_committed_page()) {
dbgln_if(PAGE_FAULT_DEBUG, "MM: zero_page() but page already present. Fine with me!");
if (!remap_vmobject_page(page_index_in_vmobject))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
auto current_thread = Thread::current();
if (current_thread != nullptr)
current_thread->did_zero_fault();
if (page_slot->is_lazy_committed_page()) {
VERIFY(m_vmobject->is_anonymous());
page_slot = static_cast<AnonymousVMObject&>(*m_vmobject).allocate_committed_page({});
dbgln_if(PAGE_FAULT_DEBUG, " >> ALLOCATED COMMITTED {}", page_slot->paddr());
} else {
auto page_or_error = MM.allocate_user_physical_page(MemoryManager::ShouldZeroFill::Yes);
if (page_or_error.is_error()) {
dmesgln("MM: handle_zero_fault was unable to allocate a physical page");
return PageFaultResponse::OutOfMemory;
}
page_slot = page_or_error.release_value();
dbgln_if(PAGE_FAULT_DEBUG, " >> ALLOCATED {}", page_slot->paddr());
}
if (!remap_vmobject_page(page_index_in_vmobject)) {
dmesgln("MM: handle_zero_fault was unable to allocate a page table to map {}", page_slot);
return PageFaultResponse::OutOfMemory;
}
return PageFaultResponse::Continue;
}
PageFaultResponse Region::handle_cow_fault(size_t page_index_in_region)
{
VERIFY_INTERRUPTS_DISABLED();
auto current_thread = Thread::current();
if (current_thread)
current_thread->did_cow_fault();
if (!vmobject().is_anonymous())
return PageFaultResponse::ShouldCrash;
auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
auto response = reinterpret_cast<AnonymousVMObject&>(vmobject()).handle_cow_fault(page_index_in_vmobject, vaddr().offset(page_index_in_region * PAGE_SIZE));
if (!remap_vmobject_page(page_index_in_vmobject))
return PageFaultResponse::OutOfMemory;
return response;
}
PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
{
VERIFY_INTERRUPTS_DISABLED();
VERIFY(vmobject().is_inode());
VERIFY(!s_mm_lock.is_locked_by_current_processor());
VERIFY(!g_scheduler_lock.is_locked_by_current_processor());
auto& inode_vmobject = static_cast<InodeVMObject&>(vmobject());
auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
auto& vmobject_physical_page_entry = inode_vmobject.physical_pages()[page_index_in_vmobject];
{
SpinlockLocker locker(inode_vmobject.m_lock);
if (!vmobject_physical_page_entry.is_null()) {
dbgln_if(PAGE_FAULT_DEBUG, "handle_inode_fault: Page faulted in by someone else before reading, remapping.");
if (!remap_vmobject_page(page_index_in_vmobject))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
}
dbgln_if(PAGE_FAULT_DEBUG, "Inode fault in {} page index: {}", name(), page_index_in_region);
auto current_thread = Thread::current();
if (current_thread)
current_thread->did_inode_fault();
u8 page_buffer[PAGE_SIZE];
auto& inode = inode_vmobject.inode();
auto buffer = UserOrKernelBuffer::for_kernel_buffer(page_buffer);
auto result = inode.read_bytes(page_index_in_vmobject * PAGE_SIZE, PAGE_SIZE, buffer, nullptr);
if (result.is_error()) {
dmesgln("handle_inode_fault: Error ({}) while reading from inode", result.error());
return PageFaultResponse::ShouldCrash;
}
auto nread = result.value();
if (nread < PAGE_SIZE) {
// If we read less than a page, zero out the rest to avoid leaking uninitialized data.
memset(page_buffer + nread, 0, PAGE_SIZE - nread);
}
SpinlockLocker locker(inode_vmobject.m_lock);
if (!vmobject_physical_page_entry.is_null()) {
// Someone else faulted in this page while we were reading from the inode.
// No harm done (other than some duplicate work), remap the page here and return.
dbgln_if(PAGE_FAULT_DEBUG, "handle_inode_fault: Page faulted in by someone else, remapping.");
if (!remap_vmobject_page(page_index_in_vmobject))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
auto vmobject_physical_page_or_error = MM.allocate_user_physical_page(MemoryManager::ShouldZeroFill::No);
if (vmobject_physical_page_or_error.is_error()) {
dmesgln("MM: handle_inode_fault was unable to allocate a physical page");
return PageFaultResponse::OutOfMemory;
}
vmobject_physical_page_entry = vmobject_physical_page_or_error.release_value();
{
SpinlockLocker mm_locker(s_mm_lock);
u8* dest_ptr = MM.quickmap_page(*vmobject_physical_page_entry);
memcpy(dest_ptr, page_buffer, PAGE_SIZE);
MM.unquickmap_page();
}
if (!remap_vmobject_page(page_index_in_vmobject))
return PageFaultResponse::OutOfMemory;
return PageFaultResponse::Continue;
}
}
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