From: Nathaniel McCallum <npmccallum@redhat.com> To: Sean Christopherson <sean.j.christopherson@intel.com> Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>, linux-kernel@vger.kernel.org, x86@kernel.org, linux-sgx@vger.kernel.org, akpm@linux-foundation.org, dave.hansen@intel.com, Neil Horman <nhorman@redhat.com>, "Huang, Haitao" <haitao.huang@intel.com>, andriy.shevchenko@linux.intel.com, tglx@linutronix.de, "Svahn, Kai" <kai.svahn@intel.com>, bp@alien8.de, Josh Triplett <josh@joshtriplett.org>, luto@kernel.org, kai.huang@intel.com, David Rientjes <rientjes@google.com>, cedric.xing@intel.com, Patrick Uiterwijk <puiterwijk@redhat.com>, Andy Lutomirski <luto@amacapital.net>, Jethro Beekman <jethro@fortanix.com> Subject: Re: [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX enclave call Date: Fri, 13 Mar 2020 12:07:55 -0400 Message-ID: <CAOASepMN1fmDaPjJJ-rpbLNPGUzE2LNB69s3X5mDBEhXziZ_UQ@mail.gmail.com> (raw) In-Reply-To: <20200313005252.GA1292@linux.intel.com> On Thu, Mar 12, 2020 at 8:52 PM Sean Christopherson <sean.j.christopherson@intel.com> wrote: > > On Wed, Mar 11, 2020 at 03:30:44PM -0400, Nathaniel McCallum wrote: > > On Tue, Mar 3, 2020 at 6:40 PM Jarkko Sakkinen > > <jarkko.sakkinen@linux.intel.com> wrote: > > > + * The exit handler's return value is interpreted as follows: > > > + * >0: continue, restart __vdso_sgx_enter_enclave() with @ret as @leaf > > > + * 0: success, return @ret to the caller > > > + * <0: error, return @ret to the caller > > > + * > > > + * The userspace exit handler is responsible for unwinding the stack, e.g. to > > > + * pop @e, u_rsp and @tcs, prior to returning to __vdso_sgx_enter_enclave(). > > > > Unless I misunderstand, this documentation... > > Hrm, that does appear wrong. I'm guessing that was leftover from a previous > incarnation of the code. Or I botched the description, which is just as > likely. I figured out what happened on my end. This documentation error led me to misread the code. More below. > > > + * The exit handler may also transfer control, e.g. via longjmp() or a C++ > > > + * exception, without returning to __vdso_sgx_enter_enclave(). > > > + * > > > + * Return: > > > + * 0 on success, > > > + * -EINVAL if ENCLU leaf is not allowed, > > > + * -EFAULT if an exception occurs on ENCLU or within the enclave > > > + * -errno for all other negative values returned by the userspace exit handler > > > + */ > > ... > > > > + /* Load the callback pointer to %rax and invoke it via retpoline. */ > > > + mov 0x20(%rbp), %rax > > > + call .Lretpoline > > > + > > > + /* Restore %rsp to its post-exit value. */ > > > + mov %rbx, %rsp > > > > ... doesn't seem to match this code. > > > > If the handler pops from the stack and then we restore the stack here, > > the handler had no effect. > > > > Also, one difference between this interface and a raw ENCLU[EENTER] is > > that we can't pass arguments on the untrusted stack during EEXIT. If > > we want to support that workflow, then we need to allow the ability > > for the handler to pop "additional" values without restoring the stack > > pointer to the exact value here. > > > Also, one difference between this interface and a raw ENCLU[EENTER] is > > that we can't pass arguments on the untrusted stack during EEXIT. If > > we want to support that workflow, then we need to allow the ability > > for the handler to pop "additional" values without restoring the stack > > pointer to the exact value here. > > The callback shenanigans exist precisely to allow passing arguments on the > untrusted stack. The vDSO is very careful to preserve the stack memory > above RSP, and to snapshot RSP at the time of exit, e.g. the arguments in > memory and their addresses relative to u_rsp live across EEXIT. It's the > same basic concept as regular function calls, e.g. the callee doesn't pop > params off the stack, it just knows what addresses relative to RSP hold > the data it wants. The enclave, being the caller, is responsible for > cleaning up u_rsp. > > FWIW, if the handler reaaaly wanted to pop off the stack, it could do so, > fixup the stack, and then re-call __vdso_sgx_enter_enclave() instead of > returning (to the original __vdso_sgx_enter_enclave()). My understanding from the documentation issue above was that *if* you wanted to push parameters back on the stack during enclave exit, you would *have* to supply a handler so it could pop the parameters and reset the stack. Which is why restoring %rsp from %rbx didn't make sense to me. Related to my other message in this thread, if __vdso_sgx_enter_enclave() preserved %rbx and took @leaf as a stack parameter, you could call __vdso_sgx_enter_enclave() from C so long as the enclave didn't push return arguments on the stack. A workaround for that case would be to fix up the stack in the handler. It would be enough for the handler to simply set %rbx to the desired stack location and return (though all of this unclean of course). > > > + /* > > > + * If the return from callback is zero or negative, return immediately, > > > + * else re-execute ENCLU with the postive return value interpreted as > > > + * the requested ENCLU leaf. > > > + */ > > > + cmp $0, %eax > > > + jle .Lout > > > + jmp .Lenter_enclave > > > + > > > +.Lretpoline: > > > + call 2f > > > +1: pause > > > + lfence > > > + jmp 1b > > > +2: mov %rax, (%rsp) > > > + ret > > > + .cfi_endproc > > > + > > > +_ASM_VDSO_EXTABLE_HANDLE(.Lenclu_eenter_eresume, .Lhandle_exception) >
next prev parent reply index Thread overview: 109+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-03-03 23:35 [PATCH v28 00/22] Intel SGX foundations Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 01/22] x86/sgx: Update MAINTAINERS Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 02/22] x86/cpufeatures: x86/msr: Add Intel SGX hardware bits Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 03/22] x86/cpufeatures: x86/msr: Intel SGX Launch Control " Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 04/22] x86/mm: x86/sgx: Signal SIGSEGV with PF_SGX Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 05/22] x86/sgx: Add SGX microarchitectural data structures Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 06/22] x86/sgx: Add wrappers for ENCLS leaf functions Jarkko Sakkinen 2020-03-09 21:14 ` Sean Christopherson 2020-03-03 23:35 ` [PATCH v28 07/22] x86/cpu/intel: Detect SGX supprt Jarkko Sakkinen 2020-03-09 21:56 ` Sean Christopherson 2020-03-11 17:03 ` Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 08/22] x86/sgx: Enumerate and track EPC sections Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 09/22] x86/sgx: Add functions to allocate and free EPC pages Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 10/22] mm: Introduce vm_ops->may_mprotect() Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 11/22] x86/sgx: Linux Enclave Driver Jarkko Sakkinen 2020-03-05 17:40 ` Sean Christopherson 2020-03-05 18:24 ` Jethro Beekman 2020-03-05 19:04 ` Sean Christopherson 2020-03-06 19:00 ` Jarkko Sakkinen 2020-03-19 18:22 ` Dr. Greg 2020-03-06 18:58 ` Jarkko Sakkinen 2020-03-03 23:35 ` [PATCH v28 12/22] docs: x86/sgx: Document SGX micro architecture and kernel internals Jarkko Sakkinen 2020-03-03 23:36 ` [PATCH v28 13/22] selftests/x86: Recurse into subdirectories Jarkko Sakkinen 2020-03-03 23:36 ` [PATCH v28 14/22] selftests/x86: Add a selftest for SGX Jarkko Sakkinen 2020-03-04 19:27 ` Nathaniel McCallum 2020-03-05 11:33 ` Jarkko Sakkinen 2020-03-06 15:42 ` Dr. Greg 2020-03-06 19:07 ` Jarkko Sakkinen 2020-03-07 17:42 ` Dr. Greg 2020-03-10 13:08 ` Jarkko Sakkinen 2020-03-11 13:28 ` Jarkko Sakkinen [not found] ` <20200311164047.GG21852@linux.intel.com> 2020-03-13 19:24 ` Jarkko Sakkinen 2020-03-04 19:44 ` Nathaniel McCallum 2020-03-04 19:51 ` Nathaniel McCallum 2020-03-06 5:32 ` Dr. Greg 2020-03-06 19:04 ` Jarkko Sakkinen 2020-03-10 19:29 ` Haitao Huang 2020-03-11 9:13 ` Dr. Greg 2020-03-11 17:15 ` Haitao Huang 2020-03-17 1:07 ` Dr. Greg 2020-03-03 23:36 ` [PATCH v28 15/22] x86/sgx: Add provisioning Jarkko Sakkinen 2020-03-03 23:36 ` [PATCH v28 16/22] x86/sgx: Add a page reclaimer Jarkko Sakkinen 2020-03-05 19:03 ` Sean Christopherson 2020-03-06 18:47 ` Jarkko Sakkinen 2020-03-12 18:38 ` Sean Christopherson 2020-03-15 0:27 ` Jarkko Sakkinen 2020-03-15 1:17 ` Jarkko Sakkinen 2020-03-09 21:16 ` Sean Christopherson 2020-03-03 23:36 ` [PATCH v28 17/22] x86/sgx: ptrace() support for the SGX driver Jarkko Sakkinen 2020-03-03 23:36 ` [PATCH v28 18/22] x86/vdso: Add support for exception fixup in vDSO functions Jarkko Sakkinen 2020-03-03 23:36 ` [PATCH v28 19/22] x86/fault: Add helper function to sanitize error code Jarkko Sakkinen 2020-03-03 23:36 ` [PATCH v28 20/22] x86/traps: Attempt to fixup exceptions in vDSO before signaling Jarkko Sakkinen 2020-03-03 23:36 ` [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX enclave call Jarkko Sakkinen 2020-03-11 17:30 ` Nathaniel McCallum 2020-03-11 17:38 ` Jethro Beekman 2020-03-11 19:15 ` Nathaniel McCallum 2020-03-13 15:48 ` Nathaniel McCallum 2020-03-13 16:46 ` Sean Christopherson 2020-03-13 18:32 ` Nathaniel McCallum 2020-03-13 18:44 ` Sean Christopherson 2020-03-13 20:14 ` Nathaniel McCallum 2020-03-13 22:08 ` Sean Christopherson 2020-03-14 14:10 ` Nathaniel McCallum 2020-03-18 23:40 ` Sean Christopherson 2020-03-19 0:38 ` Xing, Cedric 2020-03-19 1:03 ` Sean Christopherson 2020-03-20 13:55 ` Nathaniel McCallum 2020-03-15 1:25 ` Jarkko Sakkinen 2020-03-15 17:53 ` Nathaniel McCallum 2020-03-16 13:31 ` Jethro Beekman 2020-03-16 13:57 ` Nathaniel McCallum 2020-03-16 13:59 ` Jethro Beekman 2020-03-16 14:03 ` Nathaniel McCallum 2020-03-16 17:17 ` Sean Christopherson 2020-03-16 21:27 ` Jarkko Sakkinen 2020-03-16 21:29 ` Jarkko Sakkinen 2020-03-16 22:55 ` Sean Christopherson 2020-03-16 23:56 ` Xing, Cedric 2020-03-18 22:01 ` Jarkko Sakkinen 2020-03-18 22:18 ` Jarkko Sakkinen 2020-03-16 13:56 ` Jarkko Sakkinen 2020-03-16 14:01 ` Nathaniel McCallum 2020-03-16 21:38 ` Jarkko Sakkinen 2020-03-16 22:53 ` Sean Christopherson 2020-03-16 23:50 ` Xing, Cedric 2020-03-16 23:59 ` Sean Christopherson 2020-03-17 0:18 ` Xing, Cedric 2020-03-17 0:27 ` Sean Christopherson 2020-03-17 16:37 ` Nathaniel McCallum 2020-03-17 16:50 ` Nathaniel McCallum 2020-03-17 21:40 ` Xing, Cedric 2020-03-17 22:09 ` Sean Christopherson 2020-03-17 22:36 ` Xing, Cedric 2020-03-17 23:57 ` Sean Christopherson 2020-03-17 22:23 ` Xing, Cedric 2020-03-18 13:01 ` Nathaniel McCallum 2020-03-20 15:53 ` Nathaniel McCallum 2020-03-17 16:28 ` Nathaniel McCallum 2020-03-18 22:58 ` Jarkko Sakkinen 2020-03-18 22:39 ` Jarkko Sakkinen 2020-03-11 19:30 ` Nathaniel McCallum 2020-03-13 0:52 ` Sean Christopherson 2020-03-13 16:07 ` Nathaniel McCallum [this message] 2020-03-13 16:33 ` Sean Christopherson 2020-03-03 23:36 ` [PATCH v28 22/22] selftests/x86: Add vDSO selftest for SGX Jarkko Sakkinen 2020-03-04 19:24 ` [PATCH v28 00/22] Intel SGX foundations Nathaniel McCallum 2020-03-17 16:00 ` Jordan Hand 2020-03-18 21:56 ` Jarkko Sakkinen 2020-03-19 17:16 ` Dr. Greg
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