Re: [RFC PATCH v4 05/26] x86/sgx: Introduce virtual EPC for use by KVM guests

[Kai Huang <kai.huang@intel.com>]

On Wed, 10 Feb 2021 08:52:25 -0800 Sean Christopherson wrote:
> On Wed, Feb 10, 2021, Kai Huang wrote:
> > On Tue, 2021-02-09 at 13:36 -0800, Dave Hansen wrote:
> > > On 2/9/21 1:19 PM, Jarkko Sakkinen wrote:
> > > > > Without that clearly documented, it would be unwise to merge this.
> > > > E.g.
> > > > 
> > > > - Have ioctl() to turn opened fd as vEPC.
> > > > - If FLC is disabled, you could only use the fd for creating vEPC.
> > > > 
> > > > Quite easy stuff to implement.
> 
> ...
> 
> > What's your opinion? Did I miss anything?
> 
> Frankly, I think trying to smush them together would be a complete trainwreck.
> 
> The vast majority of flows would need to go down completely different paths, so
> you'd end up with code like this:
> 
> diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
> index f2eac41bb4ff..5128043c7871 100644
> --- a/arch/x86/kernel/cpu/sgx/driver.c
> +++ b/arch/x86/kernel/cpu/sgx/driver.c
> @@ -46,6 +46,9 @@ static int sgx_release(struct inode *inode, struct file *file)
>         struct sgx_encl *encl = file->private_data;
>         struct sgx_encl_mm *encl_mm;
>  
> +       if (encl->not_an_enclave)
> +               return sgx_virt_epc_release(encl);
> +
>         /*
>          * Drain the remaining mm_list entries. At this point the list contains
>          * entries for processes, which have closed the enclave file but have
> @@ -83,6 +86,9 @@ static int sgx_mmap(struct file *file, struct vm_area_struct *vma)
>         struct sgx_encl *encl = file->private_data;
>         int ret;
>  
> +       if (encl->not_an_enclave)
> +               return sgx_virt_epc_mmap(encl, vma);
> +
>         ret = sgx_encl_may_map(encl, vma->vm_start, vma->vm_end, vma->vm_flags);
>         if (ret)
>                 return ret;
> @@ -104,6 +110,11 @@ static unsigned long sgx_get_unmapped_area(struct file *file,
>                                            unsigned long pgoff,
>                                            unsigned long flags)
>  {
> +       struct sgx_encl *encl = file->private_data;
> +
> +       if (encl->not_an_enclave)
> +               return sgx_virt_epc_mmap(encl, addr, len, pgoff, flags);
> +
>         if ((flags & MAP_TYPE) == MAP_PRIVATE)
>                 return -EINVAL;
> 
> I suspect it would also be tricky to avoid introducing races, since anything that
> is different for virtual EPC would have a dependency on the ioctl() being called.
> 
> This would also prevent making /dev/sgx_enclave root-only while allowing users
> access to /dev/sgx_vepc.  Forcing admins to use LSMs to do the same is silly.

Agreed. This is really a good point. Two different device nodes allows
different permission control. Thanks.

> 
> For the few flows that can share code, just split out the common bits to helpers.