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Kernel: Make Region's physical page accessors safer to use

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Region::physical_page() now takes the VMObject lock while accessing the
physical pages array, and returns a RefPtr<PhysicalPage>. This ensures
that the array access is safe.

Region::physical_page_slot() now VERIFY()'s that the VMObject lock is
held by the caller. Since we're returning a reference to the physical
page slot in the VMObject's physical page array, this is the best we
can do here.
This commit is contained in:
Andreas Kling 2022-08-18 19:20:33 +02:00
parent c3ad4ffcec
commit 4bc3745ce6
Notes: sideshowbarker 2024-07-17 08:08:32 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/4bc3745ce6
4 changed files with 12 additions and 9 deletions
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2
Kernel/Coredump.cpp
View file

@ -200,7 +200,7 @@ ErrorOr<void> Coredump::write_regions()
region.remap();
for (size_t i = 0; i < region.page_count(); i++) {
auto const* page = region.physical_page(i);
auto page = region.physical_page(i);
auto src_buffer = [&]() -> ErrorOr<UserOrKernelBuffer> {
if (page)
return UserOrKernelBuffer::for_user_buffer(reinterpret_cast<uint8_t*>((region.vaddr().as_ptr() + (i * PAGE_SIZE))), PAGE_SIZE);

15
Kernel/Memory/Region.cpp
View file

@ -164,7 +164,7 @@ 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);
auto page = physical_page(i);
if (page && !page->is_shared_zero_page() && !page->is_lazy_committed_page())
bytes += PAGE_SIZE;
}
@ -175,7 +175,7 @@ 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);
auto page = physical_page(i);
if (page && page->ref_count() > 1 && !page->is_shared_zero_page() && !page->is_lazy_committed_page())
bytes += PAGE_SIZE;
}
@ -367,6 +367,7 @@ PageFaultResponse Region::handle_fault(PageFault const& fault)
return handle_inode_fault(page_index_in_region);
}
SpinlockLocker vmobject_locker(vmobject().m_lock);
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);
@ -388,7 +389,7 @@ PageFaultResponse Region::handle_fault(PageFault const& fault)
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);
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);
@ -404,11 +405,11 @@ PageFaultResponse Region::handle_zero_fault(size_t page_index_in_region)
VERIFY_INTERRUPTS_DISABLED();
VERIFY(vmobject().is_anonymous());
SpinlockLocker locker(vmobject().m_lock);
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, *page_slot))
@ -541,14 +542,16 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
return PageFaultResponse::Continue;
}
PhysicalPage const* Region::physical_page(size_t index) const
RefPtr<PhysicalPage> Region::physical_page(size_t index) const
{
SpinlockLocker vmobject_locker(vmobject().m_lock);
VERIFY(index < page_count());
return vmobject().physical_pages()[first_page_index() + index];
}
RefPtr<PhysicalPage>& Region::physical_page_slot(size_t index)
{
VERIFY(vmobject().m_lock.is_locked_by_current_processor());
VERIFY(index < page_count());
return vmobject().physical_pages()[first_page_index() + index];
}

2
Kernel/Memory/Region.h
View file

@ -152,7 +152,7 @@ public:
return size() / PAGE_SIZE;
}
PhysicalPage const* physical_page(size_t index) const;
RefPtr<PhysicalPage> physical_page(size_t index) const;
RefPtr<PhysicalPage>& physical_page_slot(size_t index);
[[nodiscard]] size_t offset_in_vmobject() const

2
Kernel/ProcessSpecificExposed.cpp
View file

@ -293,7 +293,7 @@ ErrorOr<void> Process::procfs_get_virtual_memory_stats(KBufferBuilder& builder)
StringBuilder pagemap_builder;
for (size_t i = 0; i < region.page_count(); ++i) {
auto const* page = region.physical_page(i);
auto page = region.physical_page(i);
if (!page)
pagemap_builder.append('N');
else if (page->is_shared_zero_page() || page->is_lazy_committed_page())