From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Nathaniel McCallum <npmccallum@redhat.com>
Cc: Jethro Beekman <jethro@fortanix.com>,
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>,
Connor Kuehl <ckuehl@redhat.com>,
Harald Hoyer <harald@redhat.com>,
Lily Sturmann <lsturman@redhat.com>
Subject: Re: [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX enclave call
Date: Fri, 13 Mar 2020 09:46:22 -0700 [thread overview]
Message-ID: <20200313164622.GC5181@linux.intel.com> (raw)
In-Reply-To: <CAOASepOm8-2UCdEnVMopEprMGWjkYUbUTX++dHaqCafi2ju8mA@mail.gmail.com>
On Fri, Mar 13, 2020 at 11:48:54AM -0400, Nathaniel McCallum wrote:
> Thinking about this more carefully, I still think that at least part
> of my critique still stands.
>
> __vdso_sgx_enter_enclave() doesn't use the x86-64 ABI. This means that
> there will always be an assembly wrapper for
> __vdso_sgx_enter_enclave(). But because __vdso_sgx_enter_enclave()
> doesn't save %rbx, the wrapper is forced to in order to be called from
> C.
>
> A common pattern for the wrapper will be to do something like this:
>
> # void enter_enclave(rdi, rsi, rdx, unused, r8, r9, @tcs, @e,
> @handler, @leaf, @vdso)
> enter_enclave:
> push %rbx
> push $0 /* align */
> push 0x48(%rsp)
> push 0x48(%rsp)
> push 0x48(%rsp)
>
> mov 0x70(%rsp), %eax
> call *0x68(%rsp)
>
> add $0x20, %rsp
> pop %rbx
> ret
>
> Because __vdso_sgx_enter_enclave() doesn't preserve %rbx, the wrapper
> is forced to reposition stack parameters in a performance-critical
> path. On the other hand, if __vdso_sgx_enter_enclave() preserved %rbx,
> you could implement the above as:
>
> # void enter_enclave(rdi, rsi, rdx, unused, r8, r9, @tcs, @e,
> @handler, @leaf, @vdso)
> enter_enclave:
> mov 0x20(%rsp), %eax
> jmp *0x28(%rsp)
>
> This also implies that if __vdso_sgx_enter_enclave() took @leaf as a
> stack parameter and preserved %rbx, it would be x86-64 ABI compliant
> enough to call from C if the enclave preserves all callee-saved
> registers besides %rbx (Enarx does).
>
> What are the downsides of this approach? It also doesn't harm the more
> extended case when you need to use an assembly wrapper to setup
> additional registers. This can still be done. It does imply an extra
> push and mov instruction. But because there are currently an odd
> number of stack function parameters, the push also removes an
> alignment instruction where the stack is aligned before the call to
> __vdso_sgx_enter_enclave() (likely). Further, the push and mov are
> going to be performed by *someone* in order to call
> __vdso_sgx_enter_enclave() from C.
>
> Therefore, I'd like to propose that __vdso_sgx_enter_enclave():
> * Preserve %rbx.
At first glance, that looks sane. Being able to call __vdso... from C
would certainly be nice.
> * Take the leaf as an additional stack parameter instead of passing
> it in %rax.
Does the leaf even need to be a stack param? Wouldn't it be possible to
use %rcx as @leaf instead of @unusued? E.g.
int __vdso_sgx_enter_enclave(unsigned long rdi, unsigned long rsi,
unsigned long rdx, unsigned int leaf,
unsigned long r8, unsigned long r9,
void *tcs, struct sgx_enclave_exception *e,
sgx_enclave_exit_handler_t handler)
{
push %rbp
mov %rsp, %rbp
push %rbx
mov %ecx, %eax
.Lenter_enclave
cmp $0x2, %eax
jb .Linvalid_leaf
cmp $0x3, %eax
ja .Linvalid_leaf
mov 0x0x10(%rbp), %rbx
lea .Lasync_exit_pointer(%rip), %rcx
.Lasync_exit_pointer:
.Lenclu_eenter_eresume:
enclu
xor %eax, %eax
.Lhandle_exit:
cmp $0, 0x20(%rbp)
jne .Linvoke_userspace_handler
.Lout
pop %rbx
leave
ret
}
> Then C can call it without additional overhead. And people who need to
> "extend" the C ABI can still do so.
>
next prev parent reply other threads:[~2020-03-13 16:46 UTC|newest]
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 [this message]
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
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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