linux-kernel - Re: [PATCH 17/25] x86/sgx: Support complete page removal

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Date:   Sun, 5 Dec 2021 01:45:47 +0200
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 17/25] x86/sgx: Support complete page removal

On Wed, Dec 01, 2021 at 11:23:15AM -0800, Reinette Chatre wrote:
> The SGX2 page removal flow was introduced in previous patch and is
> as follows:
> 1) Change the type of the pages to be removed to SGX_PAGE_TYPE_TRIM
>    using the ioctl introduced in previous patch.
> 2) Approve the page removal by running ENCLU[EACCEPT] from within
>    the enclave.
> 3) Initiate actual page removal using the new ioctl introduced here.
> 
> Support the final step of the SGX2 page removal flow with a new ioctl.
> With this ioctl the user specifies a page range that should
> be removed. At this time all pages in the provided range should have
> the SGX_PAGE_TYPE_TRIM page type and the ioctl will fail with EPERM
> (Operation not permitted) when it encounters a page that does not have
> the correct type. Page removal can fail on any page within the
> provided range. Support partial success by returning the number of pages
> that were successfully removed.
> 
> Since actual page removal will succeed even if ENCLU[EACCEPT] was not
> run from within the enclave the ENCLU[EMODPR] instruction with RWX
> permissions is used as a no-op mechanism to ensure ENCLU[EACCEPT] was
> successfully run from within the enclave before the enclave page is
> removed.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
> ---
>  arch/x86/include/uapi/asm/sgx.h |  21 +++++
>  arch/x86/kernel/cpu/sgx/ioctl.c | 159 ++++++++++++++++++++++++++++++++
>  2 files changed, 180 insertions(+)
> 
> diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
> index f70caccd166c..6648ded960f8 100644
> --- a/arch/x86/include/uapi/asm/sgx.h
> +++ b/arch/x86/include/uapi/asm/sgx.h
> @@ -33,6 +33,8 @@ enum sgx_page_flags {
>  	_IOWR(SGX_MAGIC, 0x05, struct sgx_page_modp)
>  #define SGX_IOC_PAGE_MODT \
>  	_IOWR(SGX_MAGIC, 0x06, struct sgx_page_modt)
> +#define SGX_IOC_PAGE_REMOVE \
> +	_IOWR(SGX_MAGIC, 0x07, struct sgx_page_remove)

Should be SGX_IOC_ENCLAVE_REMOVE_PAGES.

/Jarkko