On 22.08.23 02:26, Huang, Kai wrote:
... I think only this build flag change should be done in this patch, as
described in the changelog.
Because ...
... if I am not missing anything, this chunk isn't needed for _this_ patch. The
old code can still produce the correct stack address. __encl_base is only needed
for the next patch, thus the relevant change should be moved to the next patch.
I understand the confusion, but the reason I included this small change
already in this commit is to make sure the commit compiles standalone.
That is, when building the original assembly statement "lea
(encl_stack)(%rbx), %rax" with -static-pie -fPIE, the linker complains
about a relocation it cannot resolve:
/usr/local/bin/ld: /tmp/cchIWyfG.o: relocation R_X86_64_32S against
`.data' can not be used when making a PIE object; recompile with -fPIE
collect2: error: ld returned 1 exit status
The problem is that only RIP-relative addressing is legit for local
symbols, ie "encl_stack(%rip)". Hence, __encl_base is already needed
here to calculate the stack address in the updated asm sequence in this
patch.
Hope this helps clarifying!
I honestly don't understand what's the purpose of this code change. I believe
this change can be done (because it looks there's no need push/pop %rbx in the
first place), but again it should be in the next patch I suppose.
Thanks, the purpose indeed was merely to remove redundant code that is
not needed. I see that it would be better to include this in a separate
patch, so I'll update this in the next patch revision.
FWIW: if this is okay, while I'm on it, I'll also take a shot at
removing remaining (unnecessary) assembly register cleansing code to
make it more obvious that the test enclave is *not* exemplary secure, as
per our earlier discussions. Ie in response to Dave's earlier comments
that "The only patches I want for the kernel are to make the test
enclave more *obviously* insecure." [1].
Best,
Jo
[1]
https://lore.kernel.org/all/da0cfb1e-e347-f7f2-ac72-aec0ee0d867d@xxxxxxxxx/
