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    SubjectRe: [RFC PATCH 2/9] x86/sgx: Do not naturally align MAP_FIXED address
    On Fri, May 31, 2019 at 04:31:52PM -0700, Sean Christopherson wrote:
    > SGX enclaves have an associated Enclave Linear Range (ELRANGE) that is
    > tracked and enforced by the CPU using a base+mask approach, similar to
    > how hardware range registers such as the variable MTRRs. As a result,
    > the ELRANGE must be naturally sized and aligned.
    >
    > To reduce boilerplate code that would be needed in every userspace
    > enclave loader, the SGX driver naturally aligns the mmap() address and
    > also requires the range to be naturally sized. Unfortunately, SGX fails
    > to grant a waiver to the MAP_FIXED case, e.g. incorrectly rejects mmap()
    > if userspace is attempting to map a small slice of an existing enclave.
    >
    > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>

    Why you want to allow mmap() to be called multiple times? mmap() could
    be allowed only once with PROT_NONE and denied afterwards. Is this for
    sending fd to another process that would map already existing enclave?

    I don't see any checks for whether the is enclave underneath. Also, I
    think that in all cases mmap() callback should allow only PROT_NONE
    as permissions for clarity even if it could called multiple times.

    /Jarkko

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