On Wed, Jun 19, 2019 at 05:43:11PM +0300, Jarkko Sakkinen wrote:
> On Mon, 2019-06-17 at 15:24 -0700, Sean Christopherson wrote:
> > + __u32 flags;
>
> This should be changed to secinfo_flags_mask containing a mask of the
> allowed bits for the secinfo flags because of two obvious reasons:
>
> 1. Protection flags are used mainly with syscalls and contain also other
> things than just the permissions that do not apply in this context.
> 2. Having a mask for all secinfo flags is more future proof.
>
> With the protection flags you end up reserving bits forever for things
> that we will never have any use for (e.g. PROT_SEM).
>
> Looking the change you convert 'flags' (wondering why it isn't called
> 'prot') to VM flags, which means that you essentially gain absolutely
> nothing and loose some potential versatility as a side-effect by doing
> that.
Ah, I see where you're coming from. My intent was that supported flags
would be SGX specific, not generic PROT_* flags. I.e. bits 2:0 are used
for PROT_{READ,WRITE,EXEC}, bit 7 can be used for SGX_ZERO_PAGE, etc...
I have two objections to 'secinfo_flags_mask':
- A full SECINFO mask is problematic for literally every other bit/field
currently defined in SECINFO.FLAGS, e.g. masking PAGE_TYPE, PENDING
and MODIFIED adds no value that I can think of, but would require the
kernel do to weird things like reject page types and EMODPR requests
(due to their PENDING/MODIFIED interaction).
- The kernel doesn't actually restrict SECINFO based on the param, it's
restricting VM_MAY* flags in the vmas. 'secinfo_flags_mask' implies
the kernel is somehow masking SECINFO.
What about something like this?
/**
* struct sgx_enclave_add_page - parameter structure for the
* %SGX_IOC_ENCLAVE_ADD_PAGE ioctl
* @addr: address within the ELRANGE
* @src: address for the page data
* @secinfo: address for the SECINFO data
* @mrmask: bitmask for the measured 256 byte chunks
* @prot: maximal PROT_{READ,WRITE,EXEC} permissions for the page
*/
struct sgx_enclave_add_page {
__u64 addr;
__u64 src;
__u64 secinfo;
__u16 mrmask;
__u8 prot;
__u8 pad;
__u64[2] reserved;
};
