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kernel: Add a guard page to the bootstrap stack so that we can catch more stack overflows

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apio 2023-02-25 17:42:32 +01:00
parent dc795ff491
commit 32ada00b72
Signed by: apio
GPG Key ID: B8A7D06E42258954
1 changed files with 19 additions and 4 deletions
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23
kernel/src/main.cpp
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@ -97,12 +97,27 @@ Result<void> init()
CPU::idle_loop();
}
// FIXME: Add a guard page to make sure the stack doesn't end up in random kernel memory. Also reclaim this memory after
// leaving the init task.
static constexpr u64 BOOTSTRAP_STACK_PAGES = 8;
// FIXME: Reclaim this memory as soon as we leave the init task (so as soon as the Scheduler runs a task switch)
static u64 allocate_initial_kernel_stack()
{
u64 address = MemoryManager::alloc_for_kernel(BOOTSTRAP_STACK_PAGES + 1, MMU::ReadWrite | MMU::NoExecute).value();
// First page is a guard page, the rest is stack.
MMU::unmap(address); // Unmap (without deallocating VM) one guard page so that attempts to access it fail with a
// non-present page fault.
kdbgln("stack guard page: %p", (void*)address);
// The actual stack.
Stack stack { address + ARCH_PAGE_SIZE, BOOTSTRAP_STACK_PAGES * ARCH_PAGE_SIZE };
return stack.top();
}
extern "C" [[noreturn]] void _start()
{
Init::check_magic();
Init::early_init();
Stack stack { MemoryManager::alloc_for_kernel(8, MMU::ReadWrite | MMU::NoExecute).value(), 8 * ARCH_PAGE_SIZE };
CPU::bootstrap_switch_stack(stack.top(), (void*)init_wrapper);
u64 bootstrap_stack_top = allocate_initial_kernel_stack();
CPU::bootstrap_switch_stack(bootstrap_stack_top, (void*)init_wrapper);
}