linux-kernel - Re: [PATCH v33 11/21] x86/sgx: Linux Enclave Driver

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Message-ID: <1ada871a-2350-1007-c625-a00bdb0d439b@intel.com>
Date:   Mon, 26 Oct 2020 14:26:13 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-security-module@...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>,
        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,
        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 v33 11/21] x86/sgx: Linux Enclave Driver

On 6/26/20 8:34 AM, Borislav Petkov wrote:
>> +	if (!(atomic_read(&encl->flags) & SGX_ENCL_CREATED))
>> +		return -EINVAL;
>> +
>> +	if (copy_from_user(&addp, arg, sizeof(addp)))
>> +		return -EFAULT;
>> +
>> +	if (!IS_ALIGNED(addp.offset, PAGE_SIZE) ||
>> +	    !IS_ALIGNED(addp.src, PAGE_SIZE))
>> +		return -EINVAL;
>> +
>> +	if (!(access_ok(addp.src, PAGE_SIZE)))
>> +		return -EFAULT;
>> +
>> +	if (addp.length & (PAGE_SIZE - 1))
>> +		return -EINVAL;
> How many pages are allowed? Unlimited? I'm hoping some limits are
> checked somewhere...

What were you concerned about here?  Was it how long the syscall could
take, or that one user could exhaust all the enclave memory in one call?

Some later versions of this patch have a 1MB limit per to reduce how
long each SGX_IOC_ENCLAVE_ADD_PAGES call spends in the kernel.  But, I'm
not _sure_ that's what you were intending.