From: Nathaniel McCallum <npmccallum@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.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>,
"Xing, Cedric" <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, 20 Mar 2020 09:55:57 -0400 [thread overview]
Message-ID: <CAOASepOSUciw73C+dQYtKuU4x4BkJ_f=TRFVMgj10qDce3k94g@mail.gmail.com> (raw)
In-Reply-To: <20200318234057.GE26164@linux.intel.com>
On Wed, Mar 18, 2020 at 7:41 PM Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> On Sat, Mar 14, 2020 at 10:10:26AM -0400, Nathaniel McCallum wrote:
> > On Fri, Mar 13, 2020 at 6:08 PM Sean Christopherson
> > <sean.j.christopherson@intel.com> wrote:
> > > > > > 4. sub/add to %rsp rather than save/restore
> > > > >
> > > > > Can you elaborate on why you want to sub/add to %rsp instead of having the
> > > > > enclave unwind the stack? Preserving %rsp across EEXIT/ERESUME seems more
> > > > > in line with function call semantics, which I assume is desirable? E.g.
> > > > >
> > > > > push param3
> > > > > push param2
> > > > > push param1
> > > > >
> > > > > enclu[EEXIT]
> > > > >
> > > > > add $0x18, %rsp
> > > >
> > > > Before enclave EEXIT, the enclave restores %rsp to the value it had
> > > > before EENTER was called. Then it pushes additional output arguments
> > > > onto the stack. The enclave calls EENCLU[EEXIT].
> > > >
> > > > We are now in __vdso...() on the way back to the caller. However, %rsp
> > > > has a different value than we entered the function with. This breaks
> > > > x86_64 ABI, obviously. The handler needs to fix this up: how does it
> > > > do so?
>
> Circling back to this request, because I just realized that the above is
> handled by saving %rsp into %rbp and requiring the enclave and handler
> to preserve %rbp at all times.
>
> So the below discussion on making the %rsp adjustment relative is moot,
> at least with respect to getting out of __vdso() if the enclave has mucked
> with the untrusted stack.
You're right. __vdso() will always restore the caller's stack via the
leave instruction at .Lout. So no change is necessary.
> > > > In the current code, __vdso..() saves the value of %rsp, calls the
> > > > handler and then restores %rsp. The handler can fix up the stack by
> > > > setting the correct value to %rbx and returning without restoring it.
> > >
> > > Ah, you're referring to the patch where the handler decides to return all
> > > the way back to the caller of __vdso...().
> > >
> > > > But this requires internal knowledge of the __vdso...() function,
> > > > which could theoretically change in the future.
> > > >
> > > > If instead the __vdso...() only did add/sub, then the handler could do:
> > > > 1. pop return address
> > > > 2. pop handler stack params
> > > > 3. pop enclave additional output stack params
> > > > 4. push handler stack params
> > > > 5. push return address
>
> Per above, this is unnecessary when returning to the caller of __vdso().
> It would be necessary if the enclave wasn't smart enough to do it's own
> stack cleanup, but that seems like a very bizarre contract between the
> enclave and its runtime.
>
> The caveat is if %rbx is saved/restored by __vdso(). If we want a
> traditional frame pointer, then %rbx would be restored from the stack
> before %rsp itself is restored (from %rbp), in which case the exit handler
> would need to adjust %rsp using a sequence similar to what you listed
> above.
>
> If __vdso() uses a non-standard frame pointer, e.g.
>
> push %rbp
> push %rbx
> mov %rsp, %rbp
>
> then %rbx would come off the stack after %rsp is restored from %rbp, i.e.
> would be guaranteed to be restored to the pre-EENTER value (unless the
> enclave or handler mucks with %rbp).
>
> Anyways, we can discuss how to implement the frame pointer in the context
> of the patches, just wanted to point this out here for completeness.
>
> > > > 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
> > >
> > >
> > > That's reasonable, let's the handler play more games with minimal overhead.
> >
> > Yes, exactly!
> >
> > > > > > That would make this a very usable and fast interface without
> > > > > > sacrificing any of its current power.
> > > > >
> > > >
> > >
> >
>
next prev parent reply other threads:[~2020-03-20 13:56 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
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 [this message]
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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