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Kernel: Crash on memory access in non-readable regions

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This patch makes it possible to make memory regions non-readable.
This is enforced using the "present" bit in the page tables.
A process that hits an not-present page fault in a non-readable
region will be crashed.
This commit is contained in:
Andreas Kling 2019-12-02 19:14:16 +01:00
parent ddd5411472
commit f41ae755ec
5 changed files with 41 additions and 2 deletions
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1
Kernel/Process.cpp
View file

@ -306,6 +306,7 @@ int Process::sys$mprotect(void* addr, size_t size, int prot)
return -EINVAL;
if (!region->is_mmap())
return -EPERM;
region->set_readable(prot & PROT_READ);
region->set_writable(prot & PROT_WRITE);
region->remap();
return 0;

9
Kernel/VM/Region.cpp
View file

@ -191,7 +191,7 @@ void Region::remap_page(size_t index)
auto& physical_page = vmobject().physical_pages()[first_page_index() + index];
ASSERT(physical_page);
pte.set_physical_page_base(physical_page->paddr().get());
pte.set_present(true);
pte.set_present(is_readable());
if (should_cow(index))
pte.set_writable(false);
else
@ -239,7 +239,7 @@ void Region::map(PageDirectory& page_directory)
auto& physical_page = vmobject().physical_pages()[first_page_index() + i];
if (physical_page) {
pte.set_physical_page_base(physical_page->paddr().get());
pte.set_present(true); // FIXME: Maybe we should use the is_readable flag here?
pte.set_present(is_readable());
if (should_cow(i))
pte.set_writable(false);
else
@ -267,6 +267,11 @@ PageFaultResponse Region::handle_fault(const PageFault& fault)
{
auto page_index_in_region = page_index_from_address(fault.vaddr());
if (fault.type() == PageFault::Type::PageNotPresent) {
if (!is_readable()) {
dbgprintf("NP(non-readable) fault in Region{%p}[%u]\n", this, page_index_in_region);
return PageFaultResponse::ShouldCrash;
}
if (vmobject().is_inode()) {
#ifdef PAGE_FAULT_DEBUG
dbgprintf("NP(inode) fault in Region{%p}[%u]\n", this, page_index_in_region);

8
Kernel/VM/Region.h
View file

@ -113,6 +113,14 @@ public:
m_access &= ~Access::Write;
}
void set_readable(bool b)
{
if (b)
m_access |= Access::Read;
else
m_access &= ~Access::Read;
}
void map(PageDirectory&);
enum class ShouldDeallocateVirtualMemoryRange {
No,