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    Subject[RFC PATCH v2.1 03/30] x86/sgx: Add wrapper for SGX2 EMODT function
    Date
    From: Reinette Chatre <reinette.chatre@intel.com>

    Add a wrapper for the EMODT ENCLS leaf function used to
    change the type of an enclave page as maintained in the
    SGX hardware's Enclave Page Cache Map (EPCM).

    EMODT:
    1) Updates the EPCM page type of the enclave page.
    2) Sets the MODIFIED bit in the EPCM entry of the enclave page.
    This bit is reset by the enclave by invoking ENCLU leaf
    function EACCEPT or EACCEPTCOPY.

    Access from within the enclave to the enclave page is not possible
    while the MODIFIED bit is set.

    After changing the enclave page type by issuing EMODT the kernel
    needs to collaborate with the hardware to ensure that no logical
    processor continues to hold a reference to the changed page. This
    is required to ensure no required security checks are circumvented
    and is required for the enclave's EACCEPT/EACCEPTCOPY to succeed.
    Ensuring that no references to the changed page remain is
    accomplished with the ETRACK flow.

    Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
    ---
    arch/x86/kernel/cpu/sgx/encls.h | 6 ++++++
    1 file changed, 6 insertions(+)

    diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h
    index 2b091912f038..7a1ecf704ec1 100644
    --- a/arch/x86/kernel/cpu/sgx/encls.h
    +++ b/arch/x86/kernel/cpu/sgx/encls.h
    @@ -221,4 +221,10 @@ static inline int __emodpr(struct sgx_secinfo *secinfo, void *addr)
    return __encls_ret_2(EMODPR, secinfo, addr);
    }

    +/* Change the type of an EPC page. */
    +static inline int __emodt(struct sgx_secinfo *secinfo, void *addr)
    +{
    + return __encls_ret_2(EMODT, secinfo, addr);
    +}
    +
    #endif /* _X86_ENCLS_H */
    --
    2.35.1
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