Re: [PATCH V3 03/30] x86/sgx: Add wrapper for SGX2 EMODT function

Jarkko Sakkinen
2022-04-05T06:52:34Z

On Mon, Apr 04, 2022 at 09:49:11AM -0700, Reinette Chatre wrote:
> 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>
> ---
> No changes since V2
>
> Changes since V1:
> - Split original patch ("x86/sgx: Add wrappers for SGX2 functions")
> in three to introduce the SGX2 functions separately (Jarkko).
> - Rewrite commit message to include how the EPCM within the hardware
> is changed by the SGX2 function as well as the calling
> conditions (Jarkko).
>
> 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 */
> --
> 2.25.1
>

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko