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Kernel/VM: Make local_offset in PhysicalRegion::free_page_at unsigned

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Anything above or equal to the 2 GB mark has the left most bit set
(0x8000...), which was falsely interpreted as negative due to
local_offset being signed.

This makes it unsigned by using FlatPtr. To check for underflow as
was intended, lets use Checked instead.

Fixes #4585
This commit is contained in:
Luke 2020-12-29 00:24:33 +00:00 • committed by Andreas Kling
parent c006952aeb
commit eb38fe4a82
1 changed files with 5 additions and 4 deletions
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9
Kernel/VM/PhysicalRegion.cpp
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@ -156,11 +156,12 @@ void PhysicalRegion::free_page_at(PhysicalAddress addr)
ASSERT_NOT_REACHED();
}
ptrdiff_t local_offset = addr.get() - m_lower.get();
ASSERT(local_offset >= 0);
ASSERT((FlatPtr)local_offset < (FlatPtr)(m_pages * PAGE_SIZE));
Checked<FlatPtr> local_offset = addr.get();
local_offset -= m_lower.get();
ASSERT(!local_offset.has_overflow());
ASSERT(local_offset.value() < (FlatPtr)(m_pages * PAGE_SIZE));
auto page = (FlatPtr)local_offset / PAGE_SIZE;
auto page = local_offset.value() / PAGE_SIZE;
m_bitmap.set(page, false);
m_free_hint = page; // We know we can find one here for sure
m_used--;