Messages in this thread | | | Subject | Re: [RFC PATCH 8/9] LSM: x86/sgx: Introduce ->enclave_load() hook for Intel SGX | From | Dave Hansen <> | Date | Mon, 3 Jun 2019 11:45:03 -0700 |
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... >>> What ensures that the mapping referenced by src can't be changed >>> to an entirely different one (with a different vm_file) between >>> the time of check (here) and the time of use? >> >> Nothing. Holding mmap_sem across copy_from_user() would suffice, >> correct? > > I don't believe you can do that; copy_from_user() could stall > indefinitely. Not sure how to do what you want here or if it requires > changing the interface.
Holding mmap_sem for *read* is OK since you can handle page faults underneath it. Holding it for write is not.
But, holding it for read also locks out the writers which might be messing with vm_file or other parts of the VMA.
Holding it for read for a long time is OK. It's obviously not ideal, but it is something we do widely today.
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