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Kernel: sys$mprotect protects sub-regions as well as whole ones

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Split a region into two/three if the desired mprotect range is a strict
subset of an existing region. We can then set the access bits on a new
region that is just our desired range and add both the new
desired subregion and the leftovers back to our page tables.
This commit is contained in:
Andrew Kaster 2019-12-30 15:11:25 -05:00 • committed by Andreas Kling
parent 9b516e3fb4
commit bc50a10cc9
2 changed files with 73 additions and 26 deletions
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98
Kernel/Process.cpp
View file

@ -239,6 +239,25 @@ static bool validate_mmap_prot(int prot, bool map_stack)
return true;
}
// Carve out a virtual address range from a region and return the two regions on either side
Vector<Region*, 2> Process::split_region_around_range(const Region& source_region, const Range& desired_range)
{
Range old_region_range = source_region.range();
auto remaining_ranges_after_unmap = old_region_range.carve(desired_range);
ASSERT(!remaining_ranges_after_unmap.is_empty());
auto make_replacement_region = [&](const Range& new_range) -> Region& {
ASSERT(new_range.base() >= old_region_range.base());
ASSERT(new_range.end() <= old_region_range.end());
size_t new_range_offset_in_vmobject = source_region.offset_in_vmobject() + (new_range.base().get() - old_region_range.base().get());
return allocate_split_region(source_region, new_range, new_range_offset_in_vmobject);
};
Vector<Region*, 2> new_regions;
for (auto& new_range : remaining_ranges_after_unmap) {
new_regions.unchecked_append(&make_replacement_region(new_range));
}
return new_regions;
}
void* Process::sys$mmap(const Syscall::SC_mmap_params* params)
{
if (!validate_read(params, sizeof(Syscall::SC_mmap_params)))
@ -330,19 +349,8 @@ int Process::sys$munmap(void* addr, size_t size)
if (auto* old_region = region_containing(range_to_unmap)) {
if (!old_region->is_mmap())
return -EPERM;
Range old_region_range = old_region->range();
auto remaining_ranges_after_unmap = old_region_range.carve(range_to_unmap);
ASSERT(!remaining_ranges_after_unmap.is_empty());
auto make_replacement_region = [&](const Range& new_range) -> Region& {
ASSERT(new_range.base() >= old_region_range.base());
ASSERT(new_range.end() <= old_region_range.end());
size_t new_range_offset_in_vmobject = old_region->offset_in_vmobject() + (new_range.base().get() - old_region_range.base().get());
return allocate_split_region(*old_region, new_range, new_range_offset_in_vmobject);
};
Vector<Region*, 2> new_regions;
for (auto& new_range : remaining_ranges_after_unmap) {
new_regions.unchecked_append(&make_replacement_region(new_range));
}
auto new_regions = split_region_around_range(*old_region, range_to_unmap);
// We manually unmap the old region here, specifying that we *don't* want the VM deallocated.
old_region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
@ -351,7 +359,7 @@ int Process::sys$munmap(void* addr, size_t size)
// Instead we give back the unwanted VM manually.
page_directory().range_allocator().deallocate(range_to_unmap);
// And finally we map the new region(s).
// And finally we map the new region(s) using our page directory (they were just allocated and don't have one).
for (auto* new_region : new_regions) {
new_region->map(page_directory());
}
@ -365,18 +373,56 @@ int Process::sys$munmap(void* addr, size_t size)
int Process::sys$mprotect(void* addr, size_t size, int prot)
{
auto* region = region_from_range({ VirtualAddress((u32)addr), size });
if (!region)
return -EINVAL;
if (!region->is_mmap())
return -EPERM;
if (!validate_mmap_prot(prot, region->is_stack()))
return -EINVAL;
region->set_readable(prot & PROT_READ);
region->set_writable(prot & PROT_WRITE);
region->set_executable(prot & PROT_EXEC);
region->remap();
return 0;
Range range_to_mprotect = { VirtualAddress((u32)addr), size };
if (auto* whole_region = region_from_range(range_to_mprotect)) {
if (!whole_region->is_mmap())
return -EPERM;
if (!validate_mmap_prot(prot, whole_region->is_stack()))
return -EINVAL;
if (whole_region->access() == prot_to_region_access_flags(prot))
return 0;
whole_region->set_readable(prot & PROT_READ);
whole_region->set_writable(prot & PROT_WRITE);
whole_region->set_executable(prot & PROT_EXEC);
whole_region->remap();
return 0;
}
// Check if we can carve out the desired range from an existing region
if (auto* old_region = region_containing(range_to_mprotect)) {
if (!old_region->is_mmap())
return -EPERM;
if (!validate_mmap_prot(prot, old_region->is_stack()))
return -EINVAL;
if (old_region->access() == prot_to_region_access_flags(prot))
return 0;
// This vector is the region(s) adjacent to our range.
// We need to allocate a new region for the range we wanted to change permission bits on.
auto adjacent_regions = split_region_around_range(*old_region, range_to_mprotect);
size_t new_range_offset_in_vmobject = old_region->offset_in_vmobject() + (range_to_mprotect.base().get() - old_region->range().base().get());
auto& new_region = allocate_split_region(*old_region, range_to_mprotect, new_range_offset_in_vmobject);
new_region.set_readable(prot & PROT_READ);
new_region.set_writable(prot & PROT_WRITE);
new_region.set_executable(prot & PROT_EXEC);
// Unmap the old region here, specifying that we *don't* want the VM deallocated.
old_region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
deallocate_region(*old_region);
// Map the new regions using our page directory (they were just allocated and don't have one).
for (auto* adjacent_region : adjacent_regions) {
adjacent_region->map(page_directory());
}
new_region.map(page_directory());
return 0;
}
// FIXME: We should also support mprotect() across multiple regions. (#175) (#964)
return -EINVAL;
}
int Process::sys$madvise(void* address, size_t size, int advice)

1
Kernel/Process.h
View file

@ -292,6 +292,7 @@ public:
bool deallocate_region(Region& region);
Region& allocate_split_region(const Region& source_region, const Range&, size_t offset_in_vmobject);
Vector<Region*, 2> split_region_around_range(const Region& source_region, const Range&);
void set_being_inspected(bool b) { m_being_inspected = b; }
bool is_being_inspected() const { return m_being_inspected; }