On Wed, Oct 16, 2019 at 03:24:54PM -0700, Xing, Cedric wrote:
> On 10/10/2019 5:40 PM, Sean Christopherson wrote:
> >Swap @ret and @ursp in the callback prototype so that the output from
> >the vDSO itself, @ret and @e, are grouped together. Having the first
> >N parameters all share a type also makes the prototype easier to parse
> >by (some) humans. And, passing @ursp via register saves one whole
> >MOV instruction!
> >
> >Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> >---
> > arch/x86/entry/vdso/vsgx_enter_enclave.S | 16 +++++++---------
> > arch/x86/include/uapi/asm/sgx.h | 10 +++++-----
> > 2 files changed, 12 insertions(+), 14 deletions(-)
> >
> >diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> >index 3dd22780b7ef..94f613b53b13 100644
> >--- a/arch/x86/entry/vdso/vsgx_enter_enclave.S
> >+++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> >@@ -134,23 +134,21 @@ ENTRY(__vdso_sgx_enter_enclave)
> > jmp .Lhandle_exit
> > .Linvoke_userspace_handler:
> >+ /* Pass the untrusted RSP (at exit) to the callback via %rcx. */
> >+ mov %rsp, %rcx
> >+
> > /*
> >- * Align stack per x86_64 ABI. Save the original %rsp in %rbx to be
> >- * restored after the callback returns. Note, %rsp needs to be 16-byte
> >- * aligned _after_ pushing the three parameters on the stack.
> >+ * Align stack per x86_64 ABI. Note, %rsp needs to be 16-byte aligned
> >+ * _after_ pushing the three parameters on the stack.
> > */
> >- mov %rsp, %rbx
>
> Per x86_64 ABI, %rcx is _not_ preserved across function call. How are you
> going to restore the stack after callback returns?
Magic?
I completely spaced on restoring RSP, as evidenced by the fact that I
didn't even change the restoration code to use RCX.
>
> > and $-0x10, %rsp
> > sub $0x8, %rsp
>
> Usually compilers would just use a 1-byte "push" instead of a 4-byte "sub"
> instruction here.
Ah! Took me a minute to understand 'N-byte' was referring to the opcode...
I'll update to use a push.
>
> >- /* Push @e, u_rsp and @tcs as parameters to the callback. */
> >+ /* Push @e, the "return" value and @tcs as params to the callback. */
> > push 0x18(%rbp)
> >- push %rbx
> >+ push %rax
> > push 0x10(%rbp)
> >- /* Pass the "return" value to the callback via %rcx. */
> >- mov %eax, %ecx
> >-
> > /* Clear RFLAGS.DF per x86_64 ABI */
> > cld
> >diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
> >index 255392f5054f..95f69f938b58 100644
> >--- a/arch/x86/include/uapi/asm/sgx.h
> >+++ b/arch/x86/include/uapi/asm/sgx.h
> >@@ -88,16 +88,16 @@ struct sgx_enclave_exception {
> > * @rdi: RDI at the time of enclave exit
> > * @rsi: RSI at the time of enclave exit
> > * @rdx: RDX at the time of enclave exit
> >- * @ret: 0 on success (EEXIT), -EFAULT on an exception
> >+ * @ursp: RSP at the time of enclave exit (untrusted stack)
> > * @r8: R8 at the time of enclave exit
> > * @r9: R9 at the time of enclave exit
> > * @tcs: Thread Control Structure used to enter enclave
> >- * @ursp: RSP at the time of enclave exit
> >+ * @ret: 0 on success (EEXIT), -EFAULT on an exception
> > * @e: Pointer to struct sgx_enclave_exception (as provided by caller)
> > */
> >-typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long rdx, int ret,
> >- long r8, long r9, void *tcs,
> >- long ursp,
> >+typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long rdx,
> >+ long ursp, long r8, long r9,
> >+ void *tcs, int ret,
> > struct sgx_enclave_exception *e);
> > #endif /* _UAPI_ASM_X86_SGX_H */
> >
