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Kernel: Tidy up the lowest part of the address space

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After MemoryManager initialization, we now only leave the lowest 1MB
of memory identity-mapped. The very first (null) page is not present.
All other pages are RW but not X. Supervisor only.
This commit is contained in:
Andreas Kling 2020-01-17 22:02:10 +01:00
parent 545ec578b3
commit 59b584d983
2 changed files with 38 additions and 8 deletions
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43
Kernel/VM/MemoryManager.cpp
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@ -45,10 +45,6 @@ void MemoryManager::initialize_paging()
dbgprintf("MM: Kernel page directory @ %p\n", kernel_page_directory().cr3());
#endif
// Disable execution from 0MB through 2MB (BIOS data, legacy things, ...)
if (g_cpu_supports_nx)
quickmap_pd(kernel_page_directory(), 0)[0].set_execute_disabled(true);
#if 0
// Disable writing to the kernel text and rodata segments.
extern u32 start_of_kernel_text;
@ -138,11 +134,41 @@ void MemoryManager::initialize_paging()
"movl %%eax, %%cr0\n" ::
: "%eax", "memory");
setup_low_1mb();
#ifdef MM_DEBUG
dbgprintf("MM: Paging initialized.\n");
#endif
}
void MemoryManager::setup_low_1mb()
{
m_low_page_table = allocate_supervisor_physical_page();
auto* pd_zero = quickmap_pd(kernel_page_directory(), 0);
pd_zero[1].set_present(false);
pd_zero[2].set_present(false);
pd_zero[3].set_present(false);
auto& pde_zero = pd_zero[0];
pde_zero.set_page_table_base(m_low_page_table->paddr().get());
pde_zero.set_present(true);
pde_zero.set_huge(false);
pde_zero.set_writable(true);
pde_zero.set_user_allowed(false);
if (g_cpu_supports_nx)
pde_zero.set_execute_disabled(true);
for (u32 offset = 0; offset < (2 * MB); offset += PAGE_SIZE) {
auto& page_table_page = m_low_page_table;
auto& pte = quickmap_pt(page_table_page->paddr())[offset / PAGE_SIZE];
pte.set_physical_page_base(offset);
pte.set_user_allowed(false);
pte.set_present(offset != 0);
pte.set_writable(offset < (1 * MB));
}
}
void MemoryManager::parse_memory_map()
{
RefPtr<PhysicalRegion> region;
@ -218,7 +244,6 @@ void MemoryManager::parse_memory_map()
for (auto& region : m_user_physical_regions)
m_user_physical_pages += region.finalize_capacity();
}
PageTableEntry& MemoryManager::ensure_pte(PageDirectory& page_directory, VirtualAddress vaddr)
@ -591,7 +616,9 @@ PageDirectoryEntry* MemoryManager::quickmap_pd(PageDirectory& directory, size_t
auto& pte = boot_pd3_pde1023_pt[4];
auto pd_paddr = directory.m_directory_pages[pdpt_index]->paddr();
if (pte.physical_page_base() != pd_paddr.as_ptr()) {
//dbgprintf("quickmap_pd: Mapping P%p at 0xffe04000 in pte @ %p\n", directory.m_directory_pages[pdpt_index]->paddr().as_ptr(), &pte);
#ifdef MM_DEBUG
dbgprintf("quickmap_pd: Mapping P%p at 0xffe04000 in pte @ %p\n", directory.m_directory_pages[pdpt_index]->paddr().as_ptr(), &pte);
#endif
pte.set_physical_page_base(pd_paddr.get());
pte.set_present(true);
pte.set_writable(true);
@ -605,7 +632,9 @@ PageTableEntry* MemoryManager::quickmap_pt(PhysicalAddress pt_paddr)
{
auto& pte = boot_pd3_pde1023_pt[8];
if (pte.physical_page_base() != pt_paddr.as_ptr()) {
//dbgprintf("quickmap_pt: Mapping P%p at 0xffe08000 in pte @ %p\n", pt_paddr.as_ptr(), &pte);
#ifdef MM_DEBUG
dbgprintf("quickmap_pt: Mapping P%p at 0xffe08000 in pte @ %p\n", pt_paddr.as_ptr(), &pte);
#endif
pte.set_physical_page_base(pt_paddr.get());
pte.set_present(true);
pte.set_writable(true);