linux-kernel - Re: [PATCH v39 21/24] x86/vdso: Implement a vDSO for Intel SGX enclave call

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Message-ID: <453c2d9b-0fd0-0d63-2bb9-096f255a6ff4@fortanix.com>
Date:   Tue, 6 Oct 2020 10:30:16 +0200
From:   Jethro Beekman <jethro@...tanix.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Cedric Xing <cedric.xing@...el.com>, akpm@...ux-foundation.org,
        andriy.shevchenko@...ux.intel.com, asapek@...gle.com, bp@...en8.de,
        chenalexchen@...gle.com, conradparker@...gle.com,
        cyhanish@...gle.com, dave.hansen@...el.com, haitao.huang@...el.com,
        kai.huang@...el.com, kai.svahn@...el.com, kmoy@...gle.com,
        ludloff@...gle.com, luto@...nel.org, nhorman@...hat.com,
        npmccallum@...hat.com, puiterwijk@...hat.com, rientjes@...gle.com,
        tglx@...utronix.de, yaozhangx@...gle.com, mikko.ylinen@...el.com
Subject: Re: [PATCH v39 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call

On 2020-10-06 04:57, Sean Christopherson wrote:
> On Sat, Oct 03, 2020 at 07:50:56AM +0300, Jarkko Sakkinen wrote:
>> From: Sean Christopherson <sean.j.christopherson@...el.com>
>> +	/* Validate that the reserved area contains only zeros. */
>> +	push	%rax
>> +	push	%rbx
>> +	mov	$SGX_ENCLAVE_RUN_RESERVED_START, %rbx
>> +1:
>> +	mov	(%rcx, %rbx), %rax
>> +	cmpq	$0, %rax
>> +	jne	.Linvalid_input
>> +
>> +	add	$8, %rbx
>> +	cmpq	$SGX_ENCLAVE_RUN_RESERVED_END, %rbx
>> +	jne	1b
>> +	pop	%rbx
>> +	pop	%rax
> 
> This can more succinctly be (untested):
> 
> 	movq	SGX_ENCLAVE_RUN_RESERVED_1(%rbp), %rbx	
> 	orq	SGX_ENCLAVE_RUN_RESERVED_2(%rbp), %rbx	
> 	orq	SGX_ENCLAVE_RUN_RESERVED_3(%rbp), %rbx	
> 	jnz	.Linvalid_input
> 
> Note, %rbx is getting clobbered anyways, no need to save/restore it.
> 
>> diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
>> index b6ba036a9b82..3dd2df44d569 100644
>> --- a/arch/x86/include/uapi/asm/sgx.h
>> +++ b/arch/x86/include/uapi/asm/sgx.h
>> @@ -74,4 +74,102 @@ struct sgx_enclave_provision {
>>  	__u64 attribute_fd;
>>  };
>>  
>> +struct sgx_enclave_run;
>> +
>> +/**
>> + * typedef sgx_enclave_user_handler_t - Exit handler function accepted by
>> + *					__vdso_sgx_enter_enclave()
>> + * @run:	Pointer to the caller provided struct sgx_enclave_run
>> + *
>> + * The register parameters contain the snapshot of their values at enclave
>> + * exit
>> + *
>> + * Return:
>> + *  0 or negative to exit vDSO
>> + *  positive to re-enter enclave (must be EENTER or ERESUME leaf)
>> + */
>> +typedef int (*sgx_enclave_user_handler_t)(long rdi, long rsi, long rdx,
>> +					  long rsp, long r8, long r9,
>> +					  struct sgx_enclave_run *run);
>> +
>> +/**
>> + * struct sgx_enclave_run - the execution context of __vdso_sgx_enter_enclave()
>> + * @tcs:			TCS used to enter the enclave
>> + * @user_handler:		User provided callback run on exception
>> + * @user_data:			Data passed to the user handler
>> + * @leaf:			The ENCLU leaf we were at (EENTER/ERESUME/EEXIT)
>> + * @exception_vector:		The interrupt vector of the exception
>> + * @exception_error_code:	The exception error code pulled out of the stack
>> + * @exception_addr:		The address that triggered the exception
>> + * @reserved			Reserved for possible future use
>> + */
>> +struct sgx_enclave_run {
>> +	__u64 tcs;
>> +	__u64 user_handler;
>> +	__u64 user_data;
>> +	__u32 leaf;
> 
> I am still very strongly opposed to omitting exit_reason.  It is not at all
> difficult to imagine scenarios where 'leaf' alone is insufficient for the
> caller or its handler to deduce why the CPU exited the enclave.  E.g. see
> Jethro's request for intercepting interrupts.

Not entirely sure what this has to do with my request, I just expect to see leaf=ERESUME in this case, I think? E.g. as you would see in EAX when calling ENCLU.

--
Jethro Beekman | Fortanix



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