linux-kernel - Re: [PATCH v38 13/24] x86/sgx: Add SGX_IOC_ENCLAVE_ADD

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Message-ID: <20200921195822.GA58176@linux.intel.com>
Date:   Mon, 21 Sep 2020 22:58:22 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Haitao Huang <haitao.huang@...ux.intel.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jethro Beekman <jethro@...tanix.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>,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, bp@...en8.de, 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 13/24] x86/sgx: Add SGX_IOC_ENCLAVE_ADD_PAGES

On Mon, Sep 21, 2020 at 10:44:19PM +0300, Jarkko Sakkinen wrote:
> On Mon, Sep 21, 2020 at 09:49:48PM +0300, Jarkko Sakkinen wrote:
> > To have understandable semantics you have to map error codes to
> > conditions rather than opcodes. -EIO means loss of enclave in the event
> > of EPC gone invalid. Enclave is already lost, that is the reason why we
> > deinitialize the kernel data structures.
> > 
> > EADD must have a different error code because nothing is actually lost
> > but the failure conditions are triggered outside. -EFAULT would be
> > probably the most reasonable choice for that.
> 
> Now that I did all the changes discussed and then I remember why EADD
> and EEXTEND had a common error code, and common behaviour. Obviously EADD
> can also fail because of EPC reset because it depends on a valid SECS
> page.
> 
> If we cannot distinct from EADD caused by EPC loss and EADD caused by
> problems with the source, it should have the same error code, and also
> the enclave should be deinitialized, whenver this happens.
> 
> So I would just revert to v38 behaviour, keeping of course the whole
> check more visible in sgx_ioc_enclave_add_pages(), and just refine
> the documentation better describe the whole situation.

So now the behaviour is reverted back to same as it was before [*] and
I refined the documenation as:

"
 * The function deinitializes kernel data structures for enclave and returns
 * -EIO in any of the following conditions:
 *
 * - Enclave Page Cache (EPC), the physical memory holding enclaves, has
 *   been invalidated. This will cause EADD and EEXTEND to fail.
 * - If the source address is corrupted somehow when executing EADD.
"

[*] https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-sgx.git/tree/arch/x86/kernel/cpu/sgx/ioctl.c

/Jarkko