On Tue, Jul 14, 2020 at 12:07:54PM +0200, Jethro Beekman wrote:
> On 2020-07-14 11:56, Jarkko Sakkinen wrote:
> > On Tue, Jul 14, 2020 at 09:30:03AM +0200, Jethro Beekman wrote:
> >> On 2020-07-07 05:37, Jarkko Sakkinen wrote:
> >>> From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> >>>
> >>> 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@xxxxxxxxxxxxxx>
> >>> Acked-by: Jethro Beekman <jethro@xxxxxxxxxxxx>
> >>> Tested-by: Jethro Beekman <jethro@xxxxxxxxxxxx>
> >>> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> >>> Co-developed-by: Cedric Xing <cedric.xing@xxxxxxxxx>
> >>> Signed-off-by: Cedric Xing <cedric.xing@xxxxxxxxx>
> >>> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> >>> ---
> >>> arch/x86/entry/vdso/Makefile | 2 +
> >>> arch/x86/entry/vdso/vdso.lds.S | 1 +
> >>> arch/x86/entry/vdso/vsgx_enter_enclave.S | 131 +++++++++++++++++++++++
> >>> arch/x86/include/asm/enclu.h | 8 ++
> >>> arch/x86/include/uapi/asm/sgx.h | 98 +++++++++++++++++
> >>> 5 files changed, 240 insertions(+)
> >>> create mode 100644 arch/x86/entry/vdso/vsgx_enter_enclave.S
> >>> create mode 100644 arch/x86/include/asm/enclu.h
> >>>
> >>> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> >>> index ebe82b7aecda..f71ad5ebd0c4 100644
> >>> --- a/arch/x86/entry/vdso/Makefile
> >>> +++ b/arch/x86/entry/vdso/Makefile
> >>> @@ -29,6 +29,7 @@ VDSO32-$(CONFIG_IA32_EMULATION) := y
> >>> vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o
> >>> vobjs32-y := vdso32/note.o vdso32/system_call.o vdso32/sigreturn.o
> >>> vobjs32-y += vdso32/vclock_gettime.o
> >>> +vobjs-$(VDSO64-y) += vsgx_enter_enclave.o
> >>>
> >>> # files to link into kernel
> >>> obj-y += vma.o extable.o
> >>> @@ -100,6 +101,7 @@ $(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..be7e467e1efb
> >>> --- /dev/null
> >>> +++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> >>> @@ -0,0 +1,131 @@
> >>> +/* SPDX-License-Identifier: GPL-2.0 */
> >>> +
> >>> +#include <linux/linkage.h>
> >>> +#include <asm/export.h>
> >>> +#include <asm/errno.h>
> >>> +#include <asm/enclu.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"
> >>> +
> >>> +SYM_FUNC_START(__vdso_sgx_enter_enclave)
> >>> + /* Prolog */
> >>> + .cfi_startproc
> >>> + push %rbp
> >>> + .cfi_adjust_cfa_offset 8
> >>> + .cfi_rel_offset %rbp, 0
> >>> + mov %rsp, %rbp
> >>> + .cfi_def_cfa_register %rbp
> >>> + push %rbx
> >>> + .cfi_rel_offset %rbx, -8
> >>> +
> >>> + mov %ecx, %eax
> >>> +.Lenter_enclave:
> >>> + /* EENTER <= leaf <= ERESUME */
> >>> + cmp $EENTER, %eax
> >>> + jb .Linvalid_leaf
> >>> + cmp $ERESUME, %eax
> >>> + ja .Linvalid_leaf
> >>> +
> >>> + /* Load TCS and AEP */
> >>> + mov 0x10(%rbp), %rbx
> >>> + lea .Lasync_exit_pointer(%rip), %rcx
> >>> +
> >>> + /* Single ENCLU serving as both EENTER and AEP (ERESUME) */
> >>> +.Lasync_exit_pointer:
> >>> +.Lenclu_eenter_eresume:
> >>> + enclu
> >>
> >> After thinking about this some more, I'd like to come back to this
> >> setup. Prior discussion at https://lkml.org/lkml/2018/11/2/597 . I
> >> hope I'm not derailing the discussion so much as to delay the patch
> >> set :(
> >>
> >> I previously mentioned “Userspace may want fine-grained control over
> >> enclave scheduling” as a reason userspace may want to specify a
> >> different AEP, but gave a bad example. Here's a better example: If I'm
> >> running my enclave in an M:N threading model (where M user threads run
> >> N TCSs, with N > M), an AEX is a good oppurtunity to switch contexts.
> >> Yes, I could implement this with alarm() or so, but that adds overhead
> >> while missing out on a lot of opportunities for context switching.
> >
> > The vDSO interface also provides optional callback. Wonder if that
> > works for this or can it be refined to work for this?
>
> Yeah I think if the callback was called instead of ENCLU, the callback
> has the opportunity to return non-positive which will trigger a return
> from __vdso_sgx_enter_enclave. Moving .Lasync_exit_pointer to
> .Lhandle_exit might be sufficient. But I imagine not all users would
> want this behavior (although calling the few userspace instructions is
> likely negligible compared to the actual ERESUME).
Have you tried the callback interface if it suits for your workload?
/Jarkko
