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Kernel: Detect support for no-execute (NX) CPU features

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Previously we assumed all hosts would have support for IA32_EFER.NXE.
This is mostly true for newer hardware, but older hardware will crash
and burn if you try to use this feature.

Now we check for support via CPUID.80000001[20].
This commit is contained in:
Conrad Pankoff 2019-12-26 15:28:30 +11:00 • committed by Andreas Kling
parent 5be6a43860
commit 17aef7dc99
3 changed files with 32 additions and 12 deletions
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35
Kernel/VM/MemoryManager.cpp
View file

@ -22,6 +22,9 @@ MemoryManager& MM
MemoryManager::MemoryManager(u32 physical_address_for_kernel_page_tables)
{
CPUID id(0x80000001);
m_has_nx_support = (id.edx() & (1 << 20)) != 0;
m_kernel_page_directory = PageDirectory::create_at_fixed_address(PhysicalAddress(physical_address_for_kernel_page_tables));
for (size_t i = 0; i < 4; ++i) {
m_low_page_tables[i] = (PageTableEntry*)(physical_address_for_kernel_page_tables + PAGE_SIZE * (5 + i));
@ -57,12 +60,18 @@ void MemoryManager::initialize_paging()
create_identity_mapping(kernel_page_directory(), VirtualAddress(PAGE_SIZE), (8 * MB) - PAGE_SIZE);
// Disable execution from 0MB through 1MB (BIOS data, legacy things, ...)
for (size_t i = 0; i < (1 * MB); ++i)
ensure_pte(kernel_page_directory(), VirtualAddress(i)).set_execute_disabled(true);
for (size_t i = 0; i < (1 * MB); ++i) {
auto& pte = ensure_pte(kernel_page_directory(), VirtualAddress(i));
if (m_has_nx_support)
pte.set_execute_disabled(true);
}
// Disable execution from 2MB through 8MB (kmalloc, kmalloc_eternal, slabs, page tables, ...)
for (size_t i = 1; i < 4; ++i)
kernel_page_directory().table().directory(0)[i].set_execute_disabled(true);
for (size_t i = 1; i < 4; ++i) {
auto& pte = kernel_page_directory().table().directory(0)[i];
if (m_has_nx_support)
pte.set_execute_disabled(true);
}
// FIXME: We should move everything kernel-related above the 0xc0000000 virtual mark.
@ -175,12 +184,18 @@ void MemoryManager::initialize_paging()
"orl $0x20, %eax\n"
"mov %eax, %cr4\n");
// Turn on IA32_EFER.NXE
asm volatile(
"movl $0xc0000080, %ecx\n"
"rdmsr\n"
"orl $0x800, %eax\n"
"wrmsr\n");
if (m_has_nx_support) {
kprintf("MM: NX support detected; enabling NXE flag\n");
// Turn on IA32_EFER.NXE
asm volatile(
"movl $0xc0000080, %ecx\n"
"rdmsr\n"
"orl $0x800, %eax\n"
"wrmsr\n");
} else {
kprintf("MM: NX support not detected\n");
}
asm volatile("movl %%eax, %%cr3" ::"a"(kernel_page_directory().cr3()));
asm volatile(