From: Sean Christopherson <sean.j.christopherson@intel.com>
To: "Xing, Cedric" <cedric.xing@intel.com>
Cc: Nathaniel McCallum <npmccallum@redhat.com>,
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>,
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: Wed, 18 Mar 2020 18:03:06 -0700 [thread overview]
Message-ID: <20200319010306.GA8347@linux.intel.com> (raw)
In-Reply-To: <858d19ed-868b-b4be-cbac-6cb92349d8fb@intel.com>
On Wed, Mar 18, 2020 at 05:38:29PM -0700, Xing, Cedric wrote:
> On 3/18/2020 4:40 PM, Sean Christopherson wrote:
> %rbx can always be restored as long as it is saved at a fixed offset from
> %rbp. For example, given the standard prolog below:
>
> push %rbp
> mov %rsp, %rbp
> push %rbx
>
> It can be paired with the following standard epilog:
>
> mov -8(%rbp), %rbx
> leave
> ret
>
> Alternatively, given "red zone" of 128 bytes, the following epilog will also
> work:
>
> leave
> mov -0x10(%rsp), %rbx
> ret
>
> In no cases do we have to worry about enclave mucking the stack as long as
> %rbp is preserved.
>
> >>>>While this is more work, it is standard calling convention work that
> >>>>doesn't require internal knowledge of __vdso..(). Alternatively, if we
> >>>>don't like the extra work, we can document the %rbx hack explicitly
> >>>>into the handler documentation and make it part of the interface. But
> >>>>we need some explicit way for the handler to pop enclave output stack
> >>>>params that doesn't depend on internal knowledge of the __vdso...()
> >>>>invariants.
> >>>
> >>>IIUC, this is what you're suggesting? Having to align the stack makes this
> >>>a bit annoying, but it's not bad by any means.
> >>>
> >>>diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> >>>index 94a8e5f99961..05d54f79b557 100644
> >>>--- a/arch/x86/entry/vdso/vsgx_enter_enclave.S
> >>>+++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> >>>@@ -139,8 +139,9 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
> >>> /* Pass the untrusted RSP (at exit) to the callback via %rcx. */
> >>> mov %rsp, %rcx
> >>>
> >>>- /* Save the untrusted RSP in %rbx (non-volatile register). */
> >>>+ /* Save the untrusted RSP offset in %rbx (non-volatile register). */
> >>> mov %rsp, %rbx
> >>>+ and $0xf, %rbx
> >>>
> >>> /*
> >>> * Align stack per x86_64 ABI. Note, %rsp needs to be 16-byte aligned
> >>>@@ -161,8 +162,8 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
> >>> mov 0x20(%rbp), %rax
> >>> call .Lretpoline
> >>>
> >>>- /* Restore %rsp to its post-exit value. */
> >>>- mov %rbx, %rsp
> >>>+ /* Undo the post-exit %rsp adjustment. */
> >>>+ lea 0x20(%rsp,%rbx), %rsp
> >>>
>
> Per discussion above, this is useful only if the enclave has problem
> cleaning up its own mess left on the untrusted stack, and the exit handler
> wants to EENTER the enclave again by returning to __vdso...(). It sounds
> very uncommon to me, and more like a bug than an expected behavior. Are
> there any existing code doing this or any particular application that needs
> this. If no, I'd say not to do it.
Ya, I'm on the fence as well. The only counter-argument is that doing:
push %rbp
mov %rsp, %rbp
push %rbx
...
pop %rbx
leave
ret
with the relative adjustment would allow the exit handler (or enclave) to
change %rbx. I'm not saying that is remote sane, but if we're going for
maximum flexibility...
Anyways, patches incoming, let's discuss there.
next prev parent reply other threads:[~2020-03-19 1:03 UTC|newest]
Thread overview: 110+ 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
2020-03-11 16:40 ` Sean Christopherson
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 [this message]
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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