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Subject: Re: [RFC PATCH v3 02/12] x86/sgx: Do not naturally align MAP_FIXED
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From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     linux-sgx@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
        Cedric Xing <cedric.xing@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
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        "Dr . Greg Wettstein" <greg@enjellic.com>,
        Stephen Smalley <sds@tycho.nsa.gov>
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References: <20190617222438.2080-1-sean.j.christopherson@intel.com>
         <20190617222438.2080-3-sean.j.christopherson@intel.com>
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On Mon, 2019-06-17 at 15:24 -0700, Sean Christopherson wrote:
>  {
> -	if (len < 2 * PAGE_SIZE || len & (len - 1) || flags & MAP_PRIVATE)
> +	if (flags & MAP_PRIVATE)
> +		return -EINVAL;
> +
> +	if (flags & MAP_FIXED)
> +		return addr;
> +
> +	if (len < 2 * PAGE_SIZE || len & (len - 1))
>  		return -EINVAL;
>
>  	addr = current->mm->get_unmapped_area(file, addr, 2 * len, pgoff,

Just sanity checking that for MAP_FIXED case the mm checks that the area is
unmapped before calling this?

I don't think we need to check any alignment constraints here anymore.

The summarize end result would be:

static unsigned long sgx_get_unmapped_area(struct file *file,
					   unsigned long addr,
					   unsigned long len,
					   unsigned long pgoff,
					   unsigned long flags)
{
	if (flags & MAP_PRIVATE)
		return -EINVAL;

	if (flags & MAP_FIXED)
		return addr;

	return current->mm->get_unmapped_area(file, addr, 2 * len, pgoff,
					      flags);
}

/Jarkko