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Kernel: Make file-backed memory regions remember description permissions

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This allows sys$mprotect() to honor the original readable & writable
flags of the open file description as they were at the point we did the
original sys$mmap().

IIUC, this is what Dr. POSIX wants us to do:
https://pubs.opengroup.org/onlinepubs/9699919799/functions/mprotect.html

Also, remove the bogus and racy "W^X" checking we did against mappings
based on their current inode metadata. If we want to do this, we can do
it properly. For now, it was not only racy, but also did blocking I/O
while holding a spinlock.
This commit is contained in:
Andreas Kling 2022-08-23 20:18:39 +02:00
parent 30861daa93
commit d3e8eb5918
7 changed files with 33 additions and 32 deletions
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13
Kernel/Memory/Region.h
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@ -89,7 +89,13 @@ public:
void set_stack(bool stack) { m_stack = stack; }
[[nodiscard]] bool is_mmap() const { return m_mmap; }
void set_mmap(bool mmap) { m_mmap = mmap; }
void set_mmap(bool mmap, bool description_was_readable, bool description_was_writable)
{
m_mmap = mmap;
m_mmapped_from_readable = description_was_readable;
m_mmapped_from_writable = description_was_writable;
}
[[nodiscard]] bool is_write_combine() const { return m_write_combine; }
ErrorOr<void> set_write_combine(bool);
@ -194,6 +200,9 @@ public:
[[nodiscard]] bool is_syscall_region() const { return m_syscall_region; }
void set_syscall_region(bool b) { m_syscall_region = b; }
[[nodiscard]] bool mmapped_from_readable() const { return m_mmapped_from_readable; }
[[nodiscard]] bool mmapped_from_writable() const { return m_mmapped_from_writable; }
private:
Region();
Region(NonnullLockRefPtr<VMObject>, size_t offset_in_vmobject, OwnPtr<KString>, Region::Access access, Cacheable, bool shared);
@ -228,6 +237,8 @@ private:
bool m_mmap : 1 { false };
bool m_syscall_region : 1 { false };
bool m_write_combine : 1 { false };
bool m_mmapped_from_readable : 1 { false };
bool m_mmapped_from_writable : 1 { false };
IntrusiveRedBlackTreeNode<FlatPtr, Region, RawPtr<Region>> m_tree_node;
IntrusiveListNode<Region> m_vmobject_list_node;