pagetables: allow user and kernel maps in same pgd #296
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wipawel
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Aug 30, 2023
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KTF allows user mode to allocate high addresses, which normally are only available to kernel. However, to handle this somewhat gracefully, we need to check if already-existent page table protection bits conflicts with those of a new pgentry. This means that we may fixup NX, RW or USER flags if the new mapping is more permissive than current one. This is a bit sketchy, yet useful for certains tests. Therefore, print a big warning if this ever happens. Signed-off-by: Johannes Wikner <[email protected]>
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wipawel
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KTF allows user mode to allocate high addresses, which normally are only available to kernel. However, to handle this somewhat gracefully, we need to check if already-existent page table protection bits conflicts with those of new maps.
We downgrade the current flags if the most recent mapping's flags are more permissive than current flags. This is all a bit sketchy but useful, so print a big warning if this ever happens.