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?
/Jarkko
