Re: [PATCH] x86/sgx: Fix ELDU MAC failures

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Thu, 2019-08-22 at 19:00 -0700, Sean Christopherson wrote:
> Revert a change that directly propagates the page type from SECINFO into
> encl_page->desc.  encl_page->desc is a packed value, jamming the SECINFO
> page_type sets bits that are intended for other uses.
> 
> Specifically, bits 11:3 are used to store the VA offset when a page is
> swapped out and are available for other uses when the page is resident
> in the EPC.  To allow overloading bits 11:3, the VA offset is cleared at
> ELDU and so is not explicitly cleared at EWB, e.g. the VA offset is OR'd
> into encl_page->desc.  As a result, a subsequent ELDU gets a MAC failure
> due to loading the wrong VA offset.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kernel/cpu/sgx/driver/ioctl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> index 85e36e530baf..355ce967a77f 100644
> --- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> @@ -140,7 +140,8 @@ static struct sgx_encl_page *sgx_encl_page_alloc(struct sgx_encl *encl,
>  		return ERR_PTR(-ENOMEM);
>  
>  	encl_page->desc = addr;
> -	encl_page->desc |= page_type;
> +	if (page_type == SGX_SECINFO_TCS)
> +		encl_page->desc |= SGX_ENCL_PAGE_TCS;
>  	encl_page->encl = encl;

Oops. How embrassing from my side. Please also ignore my original review
comment about unreadability. The parameter type was right and everything
was right. I was just blind for a while.

This is exactly how it should be e.g. no boolean parameter. I think with
most of this kind of APIs we should follow a patttern the API takes PT
and the function does whatever encoding we have.

/Jarkko