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From: Nathaniel McCallum <npmccallum@redhat.com>
To: Jethro Beekman <jethro@fortanix.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, "Christopherson,
	Sean J" <sean.j.christopherson@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: Wed, 11 Mar 2020 15:15:12 -0400
Message-ID: <CAOASepP=ayHUH=msoei+MfFpLosVJQ5C0dmquu7mv+6WQ2bLqQ@mail.gmail.com> (raw)
In-Reply-To: <254f1e35-4302-e55f-c00d-0f91d9503498@fortanix.com>

On Wed, Mar 11, 2020 at 1:38 PM Jethro Beekman <jethro@fortanix.com> wrote:
>
> On 2020-03-11 18:30, Nathaniel McCallum wrote:
> > On Tue, Mar 3, 2020 at 6:40 PM Jarkko Sakkinen
> > <jarkko.sakkinen@linux.intel.com> wrote:
> >>
> >> From: Sean Christopherson <sean.j.christopherson@intel.com>
> >>
> >> An SGX runtime must be aware of the exceptions, which happen inside an
> >> enclave. Introduce a vDSO call that wraps EENTER/ERESUME cycle and returns
> >> the CPU exception back to the caller exactly when it happens.
> >>
> >> Kernel fixups the exception information to RDI, RSI and RDX. The SGX call
> >> vDSO handler fills this information to the user provided buffer or
> >> alternatively trigger user provided callback at the time of the exception.
> >>
> >> The calling convention is custom and does not follow System V x86-64 ABI.
> >>
> >> Suggested-by: Andy Lutomirski <luto@amacapital.net>
> >> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> >> Co-developed-by: Cedric Xing <cedric.xing@intel.com>
> >> Signed-off-by: Cedric Xing <cedric.xing@intel.com>
> >> Tested-by: Jethro Beekman <jethro@fortanix.com>
> >> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> >> ---
> >>  arch/x86/entry/vdso/Makefile             |   2 +
> >>  arch/x86/entry/vdso/vdso.lds.S           |   1 +
> >>  arch/x86/entry/vdso/vsgx_enter_enclave.S | 187 +++++++++++++++++++++++
> >>  arch/x86/include/uapi/asm/sgx.h          |  37 +++++
> >>  4 files changed, 227 insertions(+)
> >>  create mode 100644 arch/x86/entry/vdso/vsgx_enter_enclave.S
> >>
> >> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> >> index 657e01d34d02..fa50c76a17a8 100644
> >> --- a/arch/x86/entry/vdso/Makefile
> >> +++ b/arch/x86/entry/vdso/Makefile
> >> @@ -24,6 +24,7 @@ VDSO32-$(CONFIG_IA32_EMULATION)       := y
> >>
> >>  # files to link into the vdso
> >>  vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o
> >> +vobjs-$(VDSO64-y)              += vsgx_enter_enclave.o
> >>
> >>  # files to link into kernel
> >>  obj-y                          += vma.o extable.o
> >> @@ -90,6 +91,7 @@ $(vobjs): KBUILD_CFLAGS := $(filter-out $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS
> >>  CFLAGS_REMOVE_vclock_gettime.o = -pg
> >>  CFLAGS_REMOVE_vdso32/vclock_gettime.o = -pg
> >>  CFLAGS_REMOVE_vgetcpu.o = -pg
> >> +CFLAGS_REMOVE_vsgx_enter_enclave.o = -pg
> >>
> >>  #
> >>  # X32 processes use x32 vDSO to access 64bit kernel data.
> >> diff --git a/arch/x86/entry/vdso/vdso.lds.S b/arch/x86/entry/vdso/vdso.lds.S
> >> index 36b644e16272..4bf48462fca7 100644
> >> --- a/arch/x86/entry/vdso/vdso.lds.S
> >> +++ b/arch/x86/entry/vdso/vdso.lds.S
> >> @@ -27,6 +27,7 @@ VERSION {
> >>                 __vdso_time;
> >>                 clock_getres;
> >>                 __vdso_clock_getres;
> >> +               __vdso_sgx_enter_enclave;
> >>         local: *;
> >>         };
> >>  }
> >> diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> >> new file mode 100644
> >> index 000000000000..94a8e5f99961
> >> --- /dev/null
> >> +++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> >> @@ -0,0 +1,187 @@
> >> +/* SPDX-License-Identifier: GPL-2.0 */
> >> +
> >> +#include <linux/linkage.h>
> >> +#include <asm/export.h>
> >> +#include <asm/errno.h>
> >> +
> >> +#include "extable.h"
> >> +
> >> +#define EX_LEAF                0*8
> >> +#define EX_TRAPNR      0*8+4
> >> +#define EX_ERROR_CODE  0*8+6
> >> +#define EX_ADDRESS     1*8
> >> +
> >> +.code64
> >> +.section .text, "ax"
> >> +
> >> +/**
> >> + * __vdso_sgx_enter_enclave() - Enter an SGX enclave
> >> + * @leaf:      ENCLU leaf, must be EENTER or ERESUME
> >> + * @tcs:       TCS, must be non-NULL
> >> + * @e:         Optional struct sgx_enclave_exception instance
> >> + * @handler:   Optional enclave exit handler
> >> + *
> >> + * **Important!**  __vdso_sgx_enter_enclave() is **NOT** compliant with the
> >> + * x86-64 ABI, i.e. cannot be called from standard C code.
> >> + *
> >> + * Input ABI:
> >> + *  @leaf      %eax
> >> + *  @tcs       8(%rsp)
> >> + *  @e                 0x10(%rsp)
> >> + *  @handler   0x18(%rsp)
> >> + *
> >> + * Output ABI:
> >> + *  @ret       %eax
> >> + *
> >> + * All general purpose registers except RAX, RBX and RCX are passed as-is to
> >> + * the enclave. RAX, RBX and RCX are consumed by EENTER and ERESUME and are
> >> + * loaded with @leaf, asynchronous exit pointer, and @tcs respectively.
> >> + *
> >> + * RBP and the stack are used to anchor __vdso_sgx_enter_enclave() to the
> >> + * pre-enclave state, e.g. to retrieve @e and @handler after an enclave exit.
> >> + * All other registers are available for use by the enclave and its runtime,
> >> + * e.g. an enclave can push additional data onto the stack (and modify RSP) to
> >> + * pass information to the optional exit handler (see below).
> >> + *
> >> + * Most exceptions reported on ENCLU, including those that occur within the
> >> + * enclave, are fixed up and reported synchronously instead of being delivered
> >> + * via a standard signal. Debug Exceptions (#DB) and Breakpoints (#BP) are
> >> + * never fixed up and are always delivered via standard signals. On synchrously
> >> + * reported exceptions, -EFAULT is returned and details about the exception are
> >> + * recorded in @e, the optional sgx_enclave_exception struct.
> >> +
> >> + * If an exit handler is provided, the handler will be invoked on synchronous
> >> + * exits from the enclave and for all synchronously reported exceptions. In
> >> + * latter case, @e is filled prior to invoking the handler.
> >> + *
> >> + * 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().
> >> + * 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
> >> + */
> >> +#ifdef SGX_KERNEL_DOC
> >> +/* C-style function prototype to coerce kernel-doc into parsing the comment. */
> >> +int __vdso_sgx_enter_enclave(int leaf, void *tcs,
> >> +                            struct sgx_enclave_exception *e,
> >> +                            sgx_enclave_exit_handler_t handler);
> >> +#endif
> >> +SYM_FUNC_START(__vdso_sgx_enter_enclave)
> >
> > Currently, the selftest has a wrapper around
> > __vdso_sgx_enter_enclave() which preserves all x86-64 ABI callee-saved
> > registers (CSRs), though it uses none of them. Then it calls this
> > function which uses %rbx but preserves none of the CSRs. Then it jumps
> > into an enclave which zeroes all these registers before returning.
> > Thus:
> >
> >   1. wrapper saves all CSRs
> >   2. wrapper repositions stack arguments
> >   3. __vdso_sgx_enter_enclave() modifies, but does not save %rbx
> >   4. selftest zeros all CSRs
> >   5. wrapper loads all CSRs
> >
> > I'd like to propose instead that the enclave be responsible for saving
> > and restoring CSRs. So instead of the above we have:
> >   1. __vdso_sgx_enter_enclave() saves %rbx
> >   2. enclave saves CSRs
> >   3. enclave loads CSRs
> >   4. __vdso_sgx_enter_enclave() loads %rbx
> >
> > I know that lots of other stuff happens during enclave transitions,
> > but at the very least we could reduce the number of instructions
> > through this critical path.
>
> The current calling convention for __vdso_sgx_enter_enclave has been carefully designed to mimic just calling ENCLU[EENTER] as closely as possible.

That seems like a reasonable contract. Thanks!


  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 [this message]
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
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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