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Give each task its own page directory.

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This isn't finished but I'll commit as I go. We need to get to where context
switching only needs to change CR3 and everything's ready to go.

My basic idea is:
- The first 4 kB is off-limits. This catches null dereferences.
- Up to the 4 MB mark is identity-mapped and kernel-only.
- The rest is available to everyone!

While the first 4 MB is only available to the kernel, it's still mapped in
every process, for convenience when entering the kernel.
This commit is contained in:
Andreas Kling 2018-11-01 09:01:51 +01:00
parent cddd2f37e9
commit 1da0a7c949
7 changed files with 47 additions and 15 deletions
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30
Kernel/MemoryManager.cpp
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@ -26,6 +26,14 @@ MemoryManager::~MemoryManager()
{
}
void MemoryManager::populatePageDirectory(Task& task)
{
memset(task.m_pageDirectory, 0, 4096);
task.m_pageDirectory[0] = m_pageDirectory[0];
task.m_pageDirectory[1] = m_pageDirectory[1];
}
void MemoryManager::initializePaging()
{
static_assert(sizeof(MemoryManager::PageDirectoryEntry) == 4);
@ -41,6 +49,7 @@ void MemoryManager::initializePaging()
// Make null dereferences crash.
protectMap(LinearAddress(0), 4 * KB);
// The bottom 4 MB are identity mapped & supervisor only. Every process shares this mapping.
identityMap(LinearAddress(4096), 4 * MB);
for (size_t i = (4 * MB) + PAGE_SIZE; i < (8 * MB); i += PAGE_SIZE) {
@ -63,13 +72,13 @@ void* MemoryManager::allocatePageTable()
return (void*)address;
}
auto MemoryManager::ensurePTE(LinearAddress linearAddress) -> PageTableEntry
auto MemoryManager::ensurePTE(dword* pageDirectory, LinearAddress linearAddress) -> PageTableEntry
{
ASSERT_INTERRUPTS_DISABLED();
dword pageDirectoryIndex = (linearAddress.get() >> 22) & 0x3ff;
dword pageTableIndex = (linearAddress.get() >> 12) & 0x3ff;
PageDirectoryEntry pde = PageDirectoryEntry(&m_pageDirectory[pageDirectoryIndex]);
PageDirectoryEntry pde = PageDirectoryEntry(&pageDirectory[pageDirectoryIndex]);
if (!pde.isPresent()) {
#ifdef MM_DEBUG
kprintf("MM: PDE %u not present, allocating\n", pageDirectoryIndex);
@ -103,7 +112,7 @@ void MemoryManager::protectMap(LinearAddress linearAddress, size_t length)
// FIXME: ASSERT(linearAddress is 4KB aligned);
for (dword offset = 0; offset < length; offset += 4096) {
auto pteAddress = linearAddress.offset(offset);
auto pte = ensurePTE(pteAddress);
auto pte = ensurePTE(m_pageDirectory, pteAddress);
pte.setPhysicalPageBase(pteAddress.get());
pte.setUserAllowed(false);
pte.setPresent(false);
@ -118,7 +127,7 @@ void MemoryManager::identityMap(LinearAddress linearAddress, size_t length)
// FIXME: ASSERT(linearAddress is 4KB aligned);
for (dword offset = 0; offset < length; offset += 4096) {
auto pteAddress = linearAddress.offset(offset);
auto pte = ensurePTE(pteAddress);
auto pte = ensurePTE(m_pageDirectory, pteAddress);
pte.setPhysicalPageBase(pteAddress.get());
pte.setUserAllowed(true);
pte.setPresent(true);
@ -195,7 +204,7 @@ Vector<PhysicalAddress> MemoryManager::allocatePhysicalPages(size_t count)
byte* MemoryManager::quickMapOnePage(PhysicalAddress physicalAddress)
{
ASSERT_INTERRUPTS_DISABLED();
auto pte = ensurePTE(LinearAddress(4 * MB));
auto pte = ensurePTE(m_pageDirectory, LinearAddress(4 * MB));
kprintf("MM: quickmap %x @ %x {pte @ %p}\n", physicalAddress.get(), 4*MB, pte.ptr());
pte.setPhysicalPageBase(physicalAddress.pageBase());
pte.setPresent(true);
@ -223,7 +232,7 @@ bool MemoryManager::unmapRegion(Task& task, Task::Region& region)
auto& zone = *region.zone;
for (size_t i = 0; i < zone.m_pages.size(); ++i) {
auto laddr = region.linearAddress.offset(i * PAGE_SIZE);
auto pte = ensurePTE(laddr);
auto pte = ensurePTE(task.m_pageDirectory, laddr);
pte.setPhysicalPageBase(0);
pte.setPresent(false);
pte.setWritable(false);
@ -238,12 +247,11 @@ bool MemoryManager::unmapSubregion(Task& task, Task::Subregion& subregion)
{
InterruptDisabler disabler;
auto& region = *subregion.region;
auto& zone = *region.zone;
size_t numPages = subregion.size / 4096;
ASSERT(numPages);
for (size_t i = 0; i < numPages; ++i) {
auto laddr = subregion.linearAddress.offset(i * PAGE_SIZE);
auto pte = ensurePTE(laddr);
auto pte = ensurePTE(task.m_pageDirectory, laddr);
pte.setPhysicalPageBase(0);
pte.setPresent(false);
pte.setWritable(false);
@ -278,7 +286,7 @@ bool MemoryManager::mapSubregion(Task& task, Task::Subregion& subregion)
ASSERT(numPages);
for (size_t i = 0; i < numPages; ++i) {
auto laddr = subregion.linearAddress.offset(i * PAGE_SIZE);
auto pte = ensurePTE(laddr);
auto pte = ensurePTE(task.m_pageDirectory, laddr);
pte.setPhysicalPageBase(zone.m_pages[firstPage + i].get());
pte.setPresent(true);
pte.setWritable(true);
@ -295,11 +303,11 @@ bool MemoryManager::mapRegion(Task& task, Task::Region& region)
auto& zone = *region.zone;
for (size_t i = 0; i < zone.m_pages.size(); ++i) {
auto laddr = region.linearAddress.offset(i * PAGE_SIZE);
auto pte = ensurePTE(laddr);
auto pte = ensurePTE(task.m_pageDirectory,laddr);
pte.setPhysicalPageBase(zone.m_pages[i].get());
pte.setPresent(true);
pte.setWritable(true);
pte.setUserAllowed(!task.isRing0());
pte.setUserAllowed(!task.isRing0()); // FIXME: This doesn't make sense. Allow USER if the TASK is RING0? Wh...what?
flushTLB(laddr);
//kprintf("MM: >> Mapped L%x => P%x <<\n", laddr, zone.m_pages[i].get());
}