Re: [PATCH V3 02/30] x86/sgx: Add wrapper for SGX2 EMODPR function

Jarkko Sakkinen
2022-04-05T06:52:15Z

On Mon, Apr 04, 2022 at 09:49:10AM -0700, Reinette Chatre wrote:
> Add a wrapper for the EMODPR ENCLS leaf function used to
> restrict enclave page permissions as maintained in the
> SGX hardware's Enclave Page Cache Map (EPCM).
>
> EMODPR:
> 1) Updates the EPCM permissions of an enclave page by treating
> the new permissions as a mask. Supplying a value that attempts
> to relax EPCM permissions has no effect on EPCM permissions
> (PR bit, see below, is changed).
> 2) Sets the PR bit in the EPCM entry of the enclave page to
> indicate that permission restriction is in progress. The bit
> is reset by the enclave by invoking ENCLU leaf function
> EACCEPT or EACCEPTCOPY.
>
> The enclave may access the page throughout the entire process
> if conforming to the EPCM permissions for the enclave page.
>
> After performing the permission restriction by issuing EMODPR
> the kernel needs to collaborate with the hardware to ensure that
> all logical processors sees the new restricted permissions. This
> is required for the enclave's EACCEPT/EACCEPTCOPY to succeed and
> is accomplished with the ETRACK flow.
>
> Expand enum sgx_return_code with the possible EMODPR return
> values.
>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
> Changes since V2:
> - Add detail to changelog that PR bit is set when EPCM permissions
> not changed when relaxing of permissions using EMODPR attempted.
>
> 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).
> - Make short description more specific to which permissions (EPCM
> permissions) the function modifies.
>
> arch/x86/include/asm/sgx.h | 5 +++++
> arch/x86/kernel/cpu/sgx/encls.h | 6 ++++++
> 2 files changed, 11 insertions(+)
>
> diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> index 3f9334ef67cd..d67810b50a81 100644
> --- a/arch/x86/include/asm/sgx.h
> +++ b/arch/x86/include/asm/sgx.h
> @@ -65,17 +65,22 @@ enum sgx_encls_function {
>
> /**
> * enum sgx_return_code - The return code type for ENCLS, ENCLU and ENCLV
> + * %SGX_EPC_PAGE_CONFLICT: Page is being written by other ENCLS function.
> * %SGX_NOT_TRACKED: Previous ETRACK's shootdown sequence has not
> * been completed yet.
> * %SGX_CHILD_PRESENT SECS has child pages present in the EPC.
> * %SGX_INVALID_EINITTOKEN: EINITTOKEN is invalid and enclave signer's
> * public key does not match IA32_SGXLEPUBKEYHASH.
> + * %SGX_PAGE_NOT_MODIFIABLE: The EPC page cannot be modified because it
> + * is in the PENDING or MODIFIED state.
> * %SGX_UNMASKED_EVENT: An unmasked event, e.g. INTR, was received
> */
> enum sgx_return_code {
> + SGX_EPC_PAGE_CONFLICT = 7,
> SGX_NOT_TRACKED = 11,
> SGX_CHILD_PRESENT = 13,
> SGX_INVALID_EINITTOKEN = 16,
> + SGX_PAGE_NOT_MODIFIABLE = 20,
> SGX_UNMASKED_EVENT = 128,
> };
>
> diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h
> index 0e22fa8f77c5..2b091912f038 100644
> --- a/arch/x86/kernel/cpu/sgx/encls.h
> +++ b/arch/x86/kernel/cpu/sgx/encls.h
> @@ -215,4 +215,10 @@ static inline int __ewb(struct sgx_pageinfo *pginfo, void *addr,
> return __encls_ret_3(EWB, pginfo, addr, va);
> }
>
> +/* Restrict the EPCM permissions of an EPC page. */
> +static inline int __emodpr(struct sgx_secinfo *secinfo, void *addr)
> +{
> + return __encls_ret_2(EMODPR, secinfo, addr);
> +}
> +
> #endif /* _X86_ENCLS_H */
> --
> 2.25.1
>

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

BR, Jarkko