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 <[email protected]> >>> >>> 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 <[email protected]> >>> Acked-by: Jethro Beekman <[email protected]> >>> Tested-by: Jethro Beekman <[email protected]> >>> Signed-off-by: Sean Christopherson <[email protected]> >>> Co-developed-by: Cedric Xing <[email protected]> >>> Signed-off-by: Cedric Xing <[email protected]> >>> Signed-off-by: Jarkko Sakkinen <[email protected]> >>> --- >>> 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). -- Jethro Beekman | Fortanix
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