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Kernel: Make sure the kernel info page is read-only for userspace

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To enforce this, we create two separate mappings of the same underlying
physical page. A writable mapping for the kernel, and a read-only one
for userspace (the one returned by sys$get_kernel_info_page.)
This commit is contained in:
Andreas Kling 2019-12-15 22:21:28 +01:00
parent 77cf607cda
commit 0a75a46501
3 changed files with 26 additions and 7 deletions
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21
Kernel/Process.cpp
View file

@ -58,7 +58,8 @@ static pid_t next_pid;
InlineLinkedList<Process>* g_processes;
static String* s_hostname;
static Lock* s_hostname_lock;
static VirtualAddress s_info_page_address;
static VirtualAddress s_info_page_address_for_userspace;
static VirtualAddress s_info_page_address_for_kernel;
VirtualAddress g_return_to_ring3_from_signal_trampoline;
VirtualAddress g_return_to_ring0_from_signal_trampoline;
HashMap<String, OwnPtr<Module>>* g_modules;
@ -78,7 +79,7 @@ void Process::initialize()
void Process::update_info_page_timestamp(const timeval& tv)
{
auto* info_page = (KernelInfoPage*)s_info_page_address.as_ptr();
auto* info_page = (KernelInfoPage*)s_info_page_address_for_kernel.as_ptr();
info_page->serial++;
const_cast<timeval&>(info_page->now) = tv;
}
@ -994,9 +995,15 @@ void create_signal_trampolines()
void create_kernel_info_page()
{
auto* info_page_region = MM.allocate_user_accessible_kernel_region(PAGE_SIZE, "Kernel info page").leak_ptr();
s_info_page_address = info_page_region->vaddr();
memset(s_info_page_address.as_ptr(), 0, PAGE_SIZE);
auto* info_page_region_for_userspace = MM.allocate_user_accessible_kernel_region(PAGE_SIZE, "Kernel info page").leak_ptr();
auto* info_page_region_for_kernel = MM.allocate_kernel_region_with_vmobject(info_page_region_for_userspace->vmobject(), PAGE_SIZE, "Kernel info page").leak_ptr();
s_info_page_address_for_userspace = info_page_region_for_userspace->vaddr();
s_info_page_address_for_kernel = info_page_region_for_kernel->vaddr();
memset(s_info_page_address_for_kernel.as_ptr(), 0, PAGE_SIZE);
info_page_region_for_userspace->set_writable(false);
info_page_region_for_userspace->remap();
}
int Process::sys$restore_signal_mask(u32 mask)
@ -1700,7 +1707,7 @@ int Process::sys$sleep(unsigned seconds)
timeval kgettimeofday()
{
return const_cast<const timeval&>(((KernelInfoPage*)s_info_page_address.as_ptr())->now);
return const_cast<const timeval&>(((KernelInfoPage*)s_info_page_address_for_kernel.as_ptr())->now);
}
void kgettimeofday(timeval& tv)
@ -3751,5 +3758,5 @@ int Process::sys$profiling_disable(pid_t pid)
void* Process::sys$get_kernel_info_page()
{
return s_info_page_address.as_ptr();
return s_info_page_address_for_userspace.as_ptr();
}

11
Kernel/VM/MemoryManager.cpp
View file

@ -369,6 +369,17 @@ OwnPtr<Region> MemoryManager::allocate_user_accessible_kernel_region(size_t size
return allocate_kernel_region(size, name, true);
}
OwnPtr<Region> MemoryManager::allocate_kernel_region_with_vmobject(VMObject& vmobject, size_t size, const StringView& name)
{
InterruptDisabler disabler;
ASSERT(!(size % PAGE_SIZE));
auto range = kernel_page_directory().range_allocator().allocate_anywhere(size);
ASSERT(range.is_valid());
auto region = make<Region>(range, vmobject, 0, name, PROT_READ | PROT_WRITE | PROT_EXEC);
region->map(kernel_page_directory());
return region;
}
void MemoryManager::deallocate_user_physical_page(PhysicalPage&& page)
{
for (auto& region : m_user_physical_regions) {

1
Kernel/VM/MemoryManager.h
View file

@ -63,6 +63,7 @@ public:
void map_for_kernel(VirtualAddress, PhysicalAddress, bool cache_disabled = false);
OwnPtr<Region> allocate_kernel_region(size_t, const StringView& name, bool user_accessible = false, bool should_commit = true);
OwnPtr<Region> allocate_kernel_region_with_vmobject(VMObject&, size_t, const StringView& name);
OwnPtr<Region> allocate_user_accessible_kernel_region(size_t, const StringView& name);
unsigned user_physical_pages() const { return m_user_physical_pages; }