Re: [PATCH v3 3/9] selftests/sgx: Handle relocations in test enclave

[Jo Van Bulck]

On 22.08.23 03:11, Huang, Kai wrote:>> +/*
> > + * Symbol placed at the start of the enclave image by the linker script.
> > + * Declare this extern symbol with visibility "hidden" to ensure the
> > + * compiler does not access it through the GOT.
> > + */
> > +extern const uint8_t __attribute__((visibility("hidden"))) __encl_base;
> > +static const uint64_t encl_base = (uint64_t)&__encl_base;
>
> I had hard time to understand this.  The __encl_base is a symbol which is a
> fixed value set by the compiler/linker.  encl_base has the real storage in the
> .data section, but the value is also build-time fixed.  IIUC we need some code
> to explicitly override it, but I don't see where it's done.  Perhaps I missed
> something?

Thank you for catching this. Such initialization would indeed have to be 
explicitly overridden at runtime and I somehow overlooked this (it seems 
I left the line to actually run the tests commented out after 
compilation in my test script for all versions; this is now fixed). 
Apologies for the confusion, my bad! I've reverted this back to an 
explicit (uit64_t)&__encl_base cast in the next patch iteration to avoid 
such confusion.

> > +
> > +typedef void (*encl_op_t)(void *);
> > +const encl_op_t encl_op_array[ENCL_OP_MAX] = {
> > +	do_encl_op_put_to_buf,
> > +	do_encl_op_get_from_buf,
> > +	do_encl_op_put_to_addr,
> > +	do_encl_op_get_from_addr,
> > +	do_encl_op_nop,
> > +	do_encl_eaccept,
> > +	do_encl_emodpe,
> > +	do_encl_init_tcs_page,
> > +};
>
> Any reason it cannot be 'static'?

I tested static indeed also works and will include this in the next 
iteration.

> > diff --git a/tools/testing/selftests/sgx/test_encl.lds b/tools/testing/selftests/sgx/test_encl.lds
> > index 62d37160f..b86c86060 100644
> > --- a/tools/testing/selftests/sgx/test_encl.lds
> > +++ b/tools/testing/selftests/sgx/test_encl.lds
> > @@ -32,6 +32,8 @@ SECTIONS
> >   		*(.note*)
> >   		*(.debug*)
> >   		*(.eh_frame*)
> > +		*(.dyn*)
> > +		*(.gnu.hash)
>
> This looks can be in a separate patch, because it's not directly related to what
> you are trying to fix.
>
> But I don't want to make things unnecessarily complicated for selftests, so fine
> to me if you still want to keep it.  But if you do, perhaps you can add some
> justification to the changelog saying something like: opportunistically discard
> ".dyn*" and ".gnu.hash" which the enclave loader cannot handle.  Anyway, still
> better to make a separate patch for such purpose IMHO.

Thanks, splitting this off in a separate commit for the next iteration.

Best,
Jo