Re: [RFC PATCH 2/4] x86/vdso: x86/sgx: Rework __vdso_sgx_enter_enclave() API

[Jethro Beekman <jethro@fortanix.com>]

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On 2020-08-25 09:38, Sean Christopherson wrote:
> On Tue, Aug 25, 2020 at 09:36:15AM +0200, Jethro Beekman wrote:
>> On 2020-08-25 01:54, Sean Christopherson wrote:
>>> On Mon, Aug 24, 2020 at 03:36:11PM +0200, Jethro Beekman wrote:
>>>> On 2020-08-18 06:24, Sean Christopherson wrote:
>>>>>  /**
>>>>>   * __vdso_sgx_enter_enclave() - Enter an SGX enclave
>>>>> @@ -119,16 +153,14 @@ typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long 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
>>>>> + * @r:		struct sgx_enclave_run, must be non-NULL
>>>>>   *
>>>>>   * NOTE: __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.
>>>>> + * x86-64 ABI, e.g. doesn't handle XSAVE state.  Except for non-volatile
>>>>> + * general purpose registers, EFLAGS.DF, and RSP alignment, 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
>>>>> @@ -160,16 +192,12 @@ typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long rdx,
>>>>>   * without returning to __vdso_sgx_enter_enclave().
>>>>>   *
>>>>>   * Return:
>>>>> - *  0 on success,
>>>>> + *  0 on success (ENCLU reached),
>>>>>   *  -EINVAL if ENCLU leaf is not allowed,
>>>>> - *  -EFAULT if an exception occurs on ENCLU or within the enclave
>>>>> - *  -errno for all other negative values returned by the userspace exit handler
>>>>>   */
>>>>>  typedef int (*vdso_sgx_enter_enclave_t)(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);
>>>>> +					struct sgx_enclave_run *r);
>>>>>  
>>>>>  #endif /* _UAPI_ASM_X86_SGX_H */
>>>>>
>>>>
>>>> I think this should return void now, not int? Then, the “return” section of
>>>> the documentation is also no longer correct.
>>>
>>> No, it returns -EINVAL if the leaf is bogus (and if unsupported flags are
>>> specified, if a @flags param is ever added).
>>>
>>
>> Ok, but if I read the code correctly, contrary to the docs, -EFAULT is not
>> returned but passed in struct sgx_enclave_run:
> 
> The -EFAULT and -errno lines are removed from the "Return:" section of the
> above documentation.  Did I miss one?
> 

No, I'm just bad at reading patches without syntax highlighting. This is fine as is. Sorry for the confusion.

--
Jethro Beekman | Fortanix



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