linux-kernel - Re: [PATCH V4 11/31] x86/sgx: Keep record of SGX page type

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Date:   Thu, 14 Apr 2022 14:12:57 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Reinette Chatre <reinette.chatre@...el.com>,
        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, shuah@...nel.org, linux-kselftest@...r.kernel.org
Cc:     seanjc@...gle.com, kai.huang@...el.com, cathy.zhang@...el.com,
        cedric.xing@...el.com, haitao.huang@...el.com,
        mark.shanahan@...el.com, vijay.dhanraj@...el.com, hpa@...or.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 11/31] x86/sgx: Keep record of SGX page type

On Wed, 2022-04-13 at 14:10 -0700, Reinette Chatre wrote:
> SGX2 functions are not allowed on all page types. For example,
> ENCLS[EMODPR] is only allowed on regular SGX enclave pages and
> ENCLS[EMODPT] is only allowed on TCS and regular pages. If these
> functions are attempted on another type of page the hardware would
> trigger a fault.
> 
> Keep a record of the SGX page type so that there is more
> certainty whether an SGX2 instruction can succeed and faults
> can be treated as real failures.
> 
> The page type is a property of struct sgx_encl_page
> and thus does not cover the VA page type. VA pages are maintained
> in separate structures and their type can be determined in
> a different way. The SGX2 instructions needing the page type do not
> operate on VA pages and this is thus not a scenario needing to
> be covered at this time.
> 
> struct sgx_encl_page hosting this information is maintained for each
> enclave page so the space consumed by the struct is important.
> The existing sgx_encl_page->vm_max_prot_bits is already unsigned long
> while only using three bits. Transition to a bitfield for the two
> members to support the additional information without increasing
> the space consumed by the struct.
> 
> Acked-by: Jarkko Sakkinen <jarkko@...nel.org>
> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>

Nit: reviewed-by overrides acked-by so you can remove acked-by and
keep reviewed-by.

> ---
> Changes since V3:
> - Add Jarkko's Reviewed-by tag.
> 
> Changes since V2:
> - Update changelog to motivate transition to bitfield that
>   was previously done when (now removed) vm_run_prot_bits was
>   added.
> 
> Changes since V1:
> - Add Acked-by from Jarkko.
> 
>  arch/x86/include/asm/sgx.h      | 3 +++
>  arch/x86/kernel/cpu/sgx/encl.h  | 3 ++-
>  arch/x86/kernel/cpu/sgx/ioctl.c | 2 ++
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> index d67810b50a81..eae20fa52b93 100644
> --- a/arch/x86/include/asm/sgx.h
> +++ b/arch/x86/include/asm/sgx.h
> @@ -239,6 +239,9 @@ struct sgx_pageinfo {
>   * %SGX_PAGE_TYPE_REG: a regular page
>   * %SGX_PAGE_TYPE_VA:  a VA page
>   * %SGX_PAGE_TYPE_TRIM:        a page in trimmed state
> + *
> + * Make sure when making changes to this enum that its values can still fit
> + * in the bitfield within &struct sgx_encl_page
>   */
>  enum sgx_page_type {
>         SGX_PAGE_TYPE_SECS,
> diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
> index 1b15d22f6757..07abfc70c8e3 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.h
> +++ b/arch/x86/kernel/cpu/sgx/encl.h
> @@ -27,7 +27,8 @@
>  
>  struct sgx_encl_page {
>         unsigned long desc;
> -       unsigned long vm_max_prot_bits;
> +       unsigned long vm_max_prot_bits:8;
> +       enum sgx_page_type type:16;
>         struct sgx_epc_page *epc_page;
>         struct sgx_encl *encl;
>         struct sgx_va_page *va_page;
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index a66795e0b685..21078c6643f7 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -107,6 +107,7 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
>                 set_bit(SGX_ENCL_DEBUG, &encl->flags);
>  
>         encl->secs.encl = encl;
> +       encl->secs.type = SGX_PAGE_TYPE_SECS;
>         encl->base = secs->base;
>         encl->size = secs->size;
>         encl->attributes = secs->attributes;
> @@ -344,6 +345,7 @@ static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long src,
>          */
>         encl_page->encl = encl;
>         encl_page->epc_page = epc_page;
> +       encl_page->type = (secinfo->flags & SGX_SECINFO_PAGE_TYPE_MASK) >> 8;
>         encl->secs_child_cnt++;
>  
>         if (flags & SGX_PAGE_MEASURE) {

BR, Jarkko