linux-kernel - Re: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX enclave call

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Date:   Mon, 28 Sep 2020 18:02:53 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        Jethro Beekman <jethro@...tanix.com>,
        Cedric Xing <cedric.xing@...el.com>, akpm@...ux-foundation.org,
        andriy.shevchenko@...ux.intel.com, asapek@...gle.com,
        chenalexchen@...gle.com, conradparker@...gle.com,
        cyhanish@...gle.com, dave.hansen@...el.com, haitao.huang@...el.com,
        josh@...htriplett.org, 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
Subject: Re: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call

On Mon, Sep 28, 2020 at 10:30:32AM +0200, Borislav Petkov wrote:
> On Mon, Sep 28, 2020 at 02:37:00AM +0300, Jarkko Sakkinen wrote:
> > I did not get Sean's reply, and neither can find it from lore:
> > 
> > https://lore.kernel.org/linux-sgx/20200915112842.897265-1-jarkko.sakkinen@linux.intel.com/T/#t
> 
> Yah, your mail server upgrade broke a lot of stuff. And lore even says
> it is not there:
> 
> 2020-09-25 11:43           ` Jethro Beekman
>      [not found]     ` <20200925003808.GB20333@...ux.intel.com>		<---
> 2020-09-25  1:04       ` Jarkko Sakkinen
> 
> Lemme bounce it to you.

Thank you. I think I have it correctly in my tree. And I actually
noticed that I had the original email stored in wrong archive folder on
my machine (sorry about that), so did I receive it after all, but it
does not exist in lore.

> > I'd make that a description and take away individual parameter
> > descriptions. Is that fine?
> 
> Sure.

/**
 * typedef sgx_enclave_exit_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_exit_handler_t)(long rdi, long rsi, long rdx,
					  long rsp, long r8, long r9,
					  struct sgx_enclave_run *run);

I think this looks reasonable now.

Another minor clean up I made is:

struct sgx_enclave_run {
	__u64 tcs;
	__u32 flags;
	__u32 exit_reason;
	__u64 user_handler;
	__u64 user_data;

I.e. got rid of the "user_handler union. Makes the struc less confusing
looking and is consistent with the other structs.

I've been thinking about this tail:

	union {
		struct sgx_enclave_exception exception;

		/* Pad the entire struct to 256 bytes. */
		__u8 pad[256 - 32];
	};
};

I'd just replace this with

	__u64 exception;
};

And do something like (just writing it to the email to show the idea,
have not even compiled this):

-       mov     %eax, (SGX_ENCLAVE_RUN_EXCEPTION + SGX_EX_LEAF)(%rbx)
-       mov     %di,  (SGX_ENCLAVE_RUN_EXCEPTION + SGX_EX_TRAPNR)(%rbx)
-       mov     %si,  (SGX_ENCLAVE_RUN_EXCEPTION + SGX_EX_ERROR_CODE)(%rbx)
-       mov     %rdx, (SGX_ENCLAVE_RUN_EXCEPTION + SGX_EX_ADDRESS)(%rbx)
+       mov     SGX_ENCLAVE_RUN_EXCEPTION(%rbx), %rbx
+
+       mov     %eax, (SGX_EX_LEAF)(%rbx)
+       mov     %di,  (SGX_EX_TRAPNR)(%rbx)
+       mov     %si,  (SGX_EX_ERROR_CODE)(%rbx)
+       mov     %rdx, (SGX_EX_ADDRESS)(%rbx)

> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

/Jarkko