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

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Date:   Tue, 5 Apr 2022 09:53:22 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     dave.hansen@...ux.intel.com, tglx@...utronix.de, bp@...en8.de,
        luto@...nel.org, mingo@...hat.com, linux-sgx@...r.kernel.org,
        x86@...nel.org, seanjc@...gle.com, kai.huang@...el.com,
        cathy.zhang@...el.com, cedric.xing@...el.com,
        haitao.huang@...el.com, mark.shanahan@...el.com, hpa@...or.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 02/30] x86/sgx: Add wrapper for SGX2 EMODPR function

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@...el.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@...nel.org>

BR, Jarkko