From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Nathaniel McCallum <npmccallum@redhat.com>,
Cedric Xing <cedric.xing@intel.com>,
Jethro Beekman <jethro@fortanix.com>,
Andy Lutomirski <luto@amacapital.net>,
linux-sgx@vger.kernel.org
Subject: Re: [PATCH for_v29 v2 1/5] x86/sgx: vdso: Make __vdso_sgx_enter_enclave() callable from C code
Date: Fri, 17 Apr 2020 08:05:01 -0700 [thread overview]
Message-ID: <20200417150501.GD13233@linux.intel.com> (raw)
In-Reply-To: <20200330210426.GI1384380@linux.intel.com>
On Tue, Mar 31, 2020 at 12:04:46AM +0300, Jarkko Sakkinen wrote:
> On Mon, Mar 30, 2020 at 11:08:07AM -0700, Sean Christopherson wrote:
> > 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@redhat.com>
> > Cc: Cedric Xing <cedric.xing@intel.com>
> > Cc: Jethro Beekman <jethro@fortanix.com>
> > Cc: Andy Lutomirski <luto@amacapital.net>
> > Cc: linux-sgx@vger.kernel.org
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > ---
> > arch/x86/entry/vdso/vsgx_enter_enclave.S | 30 ++++++++++++++----------
> > 1 file changed, 18 insertions(+), 12 deletions(-)
> >
> > diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> > index 34cee2b0ef09..c56064fb36bc 100644
> > --- a/arch/x86/entry/vdso/vsgx_enter_enclave.S
> > +++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> > @@ -17,22 +17,22 @@
> >
> > /**
> > * __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
>
> I'd simply put **NOTE** here instead of **Important!** as it is more
> common.
>
> > + * 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.
>
> Instead "e.g. doesn't explcitly clear EFLAGS.DF after EEXIT" (which is
> somewhat confusing statement) paragraph should be replaced with a simple
> enumerated list of differences.
I don't think the list is that simple, e.g. there is a lot of state that
is defined by the ABI that isn't touched, IMO talking about that state will
add confusion.
I also don't understand what's confusing about stating EFLAGS.DF isn't
cleared.
> Something might be left out but that's cool. Just do your best and it
> can refined over time to be more exact.
>
> > *
> > * 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
> > @@ -71,7 +71,9 @@
> > */
> > #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);
> > #endif
> > @@ -83,7 +85,10 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
> > .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
> > @@ -109,6 +114,7 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
> > jne .Linvoke_userspace_handler
> >
> > .Lout:
> > + pop %rbx
> > leave
> > .cfi_def_cfa %rsp, 8
> > ret
> > --
> > 2.24.1
> >
next prev parent reply other threads:[~2020-04-17 15:05 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-30 18:08 [PATCH for_v29 v2 0/5] x86/sgx: Make vDSO callable from C Sean Christopherson
2020-03-30 18:08 ` [PATCH for_v29 v2 1/5] x86/sgx: vdso: Make __vdso_sgx_enter_enclave() callable from C code Sean Christopherson
2020-03-30 21:04 ` Jarkko Sakkinen
2020-04-17 15:05 ` Sean Christopherson [this message]
2020-04-17 18:57 ` Jarkko Sakkinen
2020-03-30 18:08 ` [PATCH for_v29 v2 2/5] x86/sgx: vdso: Define a typedef for __vdso_sgx_enter_enclave Sean Christopherson
2020-03-30 21:10 ` Jarkko Sakkinen
2020-03-30 18:08 ` [PATCH for_v29 v2 3/5] selftests/sgx: Pass EENTER to vDSO wrapper instead of hardcoding Sean Christopherson
2020-03-30 21:07 ` Jarkko Sakkinen
2020-03-30 21:11 ` Jarkko Sakkinen
2020-03-30 18:08 ` [PATCH for_v29 v2 4/5] selftests/sgx: Stop clobbering non-volatile registers Sean Christopherson
2020-03-30 18:08 ` [PATCH for_v29 v2 5/5] selftests/sgx: Add selftest to invoke __vsgx_enter_enclave() from C Sean Christopherson
2020-03-30 20:48 ` [PATCH for_v29 v2 0/5] x86/sgx: Make vDSO callable " Jarkko Sakkinen
2020-03-30 21:42 ` Nathaniel McCallum
2020-03-31 11:58 ` Jarkko Sakkinen
2020-03-31 13:40 ` Nathaniel McCallum
2020-04-01 8:17 ` Jarkko Sakkinen
2020-04-01 13:06 ` Nathaniel McCallum
2020-04-01 14:49 ` Sean Christopherson
2020-04-02 20:01 ` Jarkko Sakkinen
2020-04-02 19:49 ` Jarkko Sakkinen
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