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([2600:1010:b06c:4273:ede1:e14c:cb3e:8ecb]) by smtp.gmail.com with ESMTPSA id s22sm26039548pfh.16.2020.08.11.08.16.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Aug 2020 08:16:56 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) Subject: Re: [PATCH v36 21/24] x86/vdso: Implement a vDSO for Intel SGX enclave call Date: Tue, 11 Aug 2020 08:16:54 -0700 Message-Id: References: Cc: Andy Lutomirski , Nathaniel McCallum , Jarkko Sakkinen , X86 ML , linux-sgx@vger.kernel.org, LKML , Jethro Beekman , Cedric Xing , Andrew Morton , Andy Shevchenko , asapek@google.com, Borislav Petkov , chenalexchen@google.com, Conrad Parker , cyhanish@google.com, Dave Hansen , "Huang, Haitao" , Josh Triplett , "Huang, Kai" , "Svahn, Kai" , Keith Moyer , Christian Ludloff , Neil Horman , Patrick Uiterwijk , David Rientjes , Thomas Gleixner , yaozhangx@google.com In-Reply-To: To: Sean Christopherson X-Mailer: iPhone Mail (17G68) Sender: linux-sgx-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org Archived-At: List-Archive: List-Post: > On Aug 10, 2020, at 5:52 PM, Andy Lutomirski wrote: >=20 > =EF=BB=BF >>> On Aug 10, 2020, at 4:48 PM, Sean Christopherson wrote: >>>=20 >>> =EF=BB=BFOn Mon, Aug 10, 2020 at 04:08:46PM -0700, Andy Lutomirski wrote= : >>> What am I missing? I still don't really understand why we are >>> supporting this mechanism at all. Just the asm code to invoke the >>> callback seems to be about half of the entire function. >>=20 >> Because the Intel SDK (and other SDKs?) wants to use the host stack to pa= ss >> parameters out of the enclave. >=20 > Ugh, right. I forgot about that particular abomination. >=20 > I suppose that passing a context pointer would be reasonable. The alternative would be to pass in a parameter that gets put in RSP before e= ntering the enclave. The idea is that the untrusted runtime would allocate a= couple pages with guard pages at either end, and enclaves using the regrett= able arguments-on-the-stack scheme would end up using the alternative stack.= At the end of the day, none of this really matters too much. Languages that c= an do inline asm but can=E2=80=99t do container_of() can get fixed or use wo= rkarounds.=