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Kernel+Userland: Add ioctl to set process ownership of DisplayConnector

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Now that the infrastructure of the Graphics subsystem is quite stable,
it is time to try to fix a long-standing problem, which is the lack of
locking on display connector devices. Reading and writing from multiple
processes to a framebuffer controlled by the display connector is not a
huge problem - it could be solved with POSIX locking.

The real problem is some program that will try to do ioctl operations on
a display connector without the WindowServer being aware of that which
can lead to very bad situations, for example - assuming a framebuffer is
encoded at a known resolution and certain display timings, but another
process changed the ModeSetting of the display connector, leading to
inconsistency on the properties of the current ModeSetting.

To solve this, there's a new "master" ioctl to take "ownership" and
another one to release that ownership of a display connector device. To
ensure we will not hold a Process object forever just because it has an
ownership over a display connector, we hold it with a weak reference,
and if the process is gone, someone else can take an ownership.
This commit is contained in:
Liav A 2022-06-10 14:16:28 +03:00 • committed by Linus Groh
parent 1968aba69b
commit 977aa81310
5 changed files with 101 additions and 8 deletions
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5
Kernel/Graphics/DisplayConnector.h
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@ -148,6 +148,8 @@ private:
virtual void will_be_destroyed() override;
virtual void after_inserting() override;
bool ioctl_requires_ownership(unsigned request) const;
OwnPtr<Memory::Region> m_framebuffer_region;
OwnPtr<Memory::Region> m_fake_writes_framebuffer_region;
u8* m_framebuffer_data {};
@ -162,6 +164,9 @@ protected:
private:
RefPtr<Memory::SharedFramebufferVMObject> m_shared_framebuffer_vmobject;
WeakPtr<Process> m_responsible_process;
Spinlock m_responsible_process_lock;
IntrusiveListNode<DisplayConnector, RefPtr<DisplayConnector>> m_list_node;
};
}