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

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Date:   Tue, 6 Oct 2020 18:49:10 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jethro Beekman <jethro@...tanix.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        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 Tue, Oct 06, 2020 at 10:30:16AM +0200, Jethro Beekman wrote:
> 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.

The documentation needs to be fixed but the answer is yes.

I.e.

- Leaf will contain ERESUME on interrupt.
- Leaf will contain EEXIT on normal exit.

Maybe I should rename it as exit_leaf and rewrite the description to
improve clarity?

/Jarkko