Make __vdso_sgx_enter_enclave() callable from C by preserving %rbx and taking @leaf in %rcx instead of %rax. Being able to invoke the vDSO from C reduces the overhead of runtimes that are tightly coupled with their enclaves, e.g. that can rely on the enclave to save and restore non-volatile registers, as the runtime doesn't need an assembly wrapper to preserve non-volatile registers and/or shuffle stack arguments. Note, both %rcx and %rbx are consumed by EENTER/ERESUME, i.e. consuming them doesn't violate the primary tenet of __vdso_sgx_enter_enclave() that "thou shalt not restrict how information is exchanged between an enclave and its host process". Suggested-by: Nathaniel McCallum <npmccallum@xxxxxxxxxx> Cc: Cedric Xing <cedric.xing@xxxxxxxxx> Cc: Jethro Beekman <jethro@xxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: linux-sgx@xxxxxxxxxxxxxxx Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> --- Cedric, please go to town on this, you're much better at the userspace stack and debugging interactions, e.g. I don't think the CFA directives need updating, but my knowledge of that stuff is skeeetchy. Note, if the previous patch to make the %rsp restoration relative is dropped, then %rbx should be restored relative to %rbp instead of %rsp. arch/x86/entry/vdso/vsgx_enter_enclave.S | 33 ++++++++++++++---------- 1 file changed, 19 insertions(+), 14 deletions(-) diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S index 14f07d5e47ae..7a0565476a29 100644 --- a/arch/x86/entry/vdso/vsgx_enter_enclave.S +++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S @@ -16,25 +16,25 @@ /** * __vdso_sgx_enter_enclave() - Enter an SGX enclave + * @rdi: Pass-through value for RDI + * @rsi: Pass-through value for RSI + * @rdx: Pass-through value for RDX * @leaf: ENCLU leaf, must be EENTER or ERESUME + * @r8: Pass-through value for R8 + * @r9: Pass-through value for R9 * @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 + * **Important!** __vdso_sgx_enter_enclave() does not ensure full compliance + * with the x86-64 ABI, e.g. doesn't explicitly clear EFLAGS.DF after EEXIT. + * Except for non-volatile general purpose registers, preserving/setting state + * in accordance with the x86-64 ABI is the responsibility of the enclave and + * its runtime, i.e. __vdso_sgx_enter_enclave() cannot be called from C code + * without careful consideration by both the enclave and its runtime. * * 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 + * 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 @@ -70,9 +70,11 @@ */ #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, +int __vdso_sgx_enter_enclave(unsigned long rdi, unsigned long rsi, + unsigned long rdx, unsigned int leaf, + unsigned long r8, unsigned long r9, void *tcs, struct sgx_enclave_exception *e, - sgx_enclave_exit_handler_t handler); + sgx_enclave_exit_handler_t handler) #endif SYM_FUNC_START(__vdso_sgx_enter_enclave) /* Prolog */ @@ -82,7 +84,9 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave) .cfi_rel_offset %rbp, 0 mov %rsp, %rbp .cfi_def_cfa_register %rbp + push %rbx + mov %ecx, %eax .Lenter_enclave: /* EENTER <= leaf <= ERESUME */ cmp $0x2, %eax @@ -108,6 +112,7 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave) jne .Linvoke_userspace_handler .Lout: + pop %rbx leave .cfi_def_cfa %rsp, 8 ret -- 2.24.1
