linux-kernel - Re: [PATCH v38 12/24] x86/sgx: Add SGX_IOC_ENCLAVE

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Date:   Mon, 21 Sep 2020 12:03:56 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jethro Beekman <jethro@...tanix.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Chunyang Hui <sanqian.hcy@...fin.com>,
        Jordan Hand <jorhand@...ux.microsoft.com>,
        Nathaniel McCallum <npmccallum@...hat.com>,
        Seth Moore <sethmo@...gle.com>,
        Darren Kenny <darren.kenny@...cle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, cedric.xing@...el.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, puiterwijk@...hat.com, rientjes@...gle.com,
        tglx@...utronix.de, yaozhangx@...gle.com
Subject: Re: [PATCH v38 12/24] x86/sgx: Add SGX_IOC_ENCLAVE_CREATE

On Tue, Sep 15, 2020 at 02:28:30PM +0300, Jarkko Sakkinen wrote:
> +static int sgx_validate_secs(const struct sgx_secs *secs)
> +{
> +	u64 max_size = (secs->attributes & SGX_ATTR_MODE64BIT) ?
> +		       sgx_encl_size_max_64 : sgx_encl_size_max_32;
> +
> +	if (secs->size < (2 * PAGE_SIZE) || !is_power_of_2(secs->size))
> +		return -EINVAL;
> +
> +	if (secs->base & (secs->size - 1))
> +		return -EINVAL;
> +
> +	if (secs->miscselect & sgx_misc_reserved_mask ||
> +	    secs->attributes & sgx_attributes_reserved_mask ||
> +	    secs->xfrm & sgx_xfrm_reserved_mask)
> +		return -EINVAL;
> +
> +	if (secs->size > max_size)
> +		return -EINVAL;
> +
> +	if (!(secs->xfrm & XFEATURE_MASK_FP) ||
> +	    !(secs->xfrm & XFEATURE_MASK_SSE) ||
> +	    (((secs->xfrm >> XFEATURE_BNDREGS) & 1) !=
> +	     ((secs->xfrm >> XFEATURE_BNDCSR) & 1)))

Let that last line stick out so that you have each statement on a single line.

> +		return -EINVAL;
> +
> +	if (!secs->ssa_frame_size)
> +		return -EINVAL;
> +
> +	if (sgx_calc_ssa_frame_size(secs->miscselect, secs->xfrm) >
> +	    secs->ssa_frame_size)

Let that stick out.

> +		return -EINVAL;
> +
> +	if (memchr_inv(secs->reserved1, 0, sizeof(secs->reserved1)) ||
> +	    memchr_inv(secs->reserved2, 0, sizeof(secs->reserved2)) ||
> +	    memchr_inv(secs->reserved3, 0, sizeof(secs->reserved3)) ||
> +	    memchr_inv(secs->reserved4, 0, sizeof(secs->reserved4)))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
> +{
> +	unsigned long encl_size = secs->size + PAGE_SIZE;

You're still using secs->size before validation. I know, we will return
early if sgx_validate_secs() fails but pls move that addition after the
validation call.

...

> +/**
> + * sgx_ioc_enclave_create - handler for %SGX_IOC_ENCLAVE_CREATE
> + * @filep:	open file to /dev/sgx

Dammit, how many times do I have to type this comment here?!

"That's

@encl: enclave pointer

or so."

There's no filep - there is an encl!


> + * @arg:	userspace pointer to a struct sgx_enclave_create instance
> + *
> + * Allocate kernel data structures for a new enclave and execute ECREATE after
> + * verifying the correctness of the provided SECS.

... which is done in sgx_validate_secs()."

Yes, spell it out, otherwise one has to wonder where that validation is
happening in the function *below* because the comment is over it - not
over sgx_validate_secs().

And yes, you need to spell stuff like that out because this SGX crap is
complex and it better be properly documented!

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette