linux-kernel - Re: [PATCH 1/6] x86/sgx: Do not consider unsanitized pages an error

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Date:   Wed, 31 Aug 2022 10:18:00 -0500
From:   "Haitao Huang" <haitao.huang@...ux.intel.com>
To:     "jarkko@...nel.org" <jarkko@...nel.org>,
        "Huang, Kai" <kai.huang@...el.com>
Cc:     "pmenzel@...gen.mpg.de" <pmenzel@...gen.mpg.de>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "Dhanraj, Vijay" <vijay.dhanraj@...el.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] x86/sgx: Do not consider unsanitized pages an error

Hi Kai
On Tue, 30 Aug 2022 22:17:08 -0500, Huang, Kai <kai.huang@...el.com> wrote:

> On Wed, 2022-08-31 at 05:57 +0300, jarkko@...nel.org wrote:
>> On Wed, Aug 31, 2022 at 02:55:52AM +0000, Huang, Kai wrote:
>> > On Wed, 2022-08-31 at 05:44 +0300, jarkko@...nel.org wrote:
>> > > On Wed, Aug 31, 2022 at 02:35:53AM +0000, Huang, Kai wrote:
>> > > > On Wed, 2022-08-31 at 05:15 +0300, jarkko@...nel.org wrote:
>> > > > > On Wed, Aug 31, 2022 at 01:27:58AM +0000, Huang, Kai wrote:
>> > > > > > On Tue, 2022-08-30 at 15:54 -0700, Reinette Chatre wrote:
>> > > > > > > Hi Jarkko,
>> > > > > > >
>> > > > > > > On 8/29/2022 8:12 PM, Jarkko Sakkinen wrote:
>> > > > > > > > In sgx_init(), if misc_register() for the provision  
>> device fails, and
>> > > > > > > > neither sgx_drv_init() nor sgx_vepc_init() succeeds, then  
>> ksgxd will be
>> > > > > > > > prematurely stopped.
>> > > > > > >
>> > > > > > > I do not think misc_register() is required to fail for the  
>> scenario to
>> > > > > > > be triggered (rather use "or" than "and"?). Perhaps just
>> > > > > > > "In sgx_init(), if a failure is encountered after ksgxd is  
>> started
>> > > > > > > (via sgx_page_reclaimer_init()) ...".
>> > > > > >
>> > > > > > IMHO "a failure" might be too vague.  For instance, failure  
>> to sgx_drv_init()
>> > > > > > won't immediately result in ksgxd to stop prematurally.  As  
>> long as KVM SGX can
>> > > > > > be initialized successfully, sgx_init() still returns 0.
>> > > > > >
>> > > > > > Btw I was thinking whether we should move  
>> sgx_page_reclaimer_init() to the end
>> > > > > > of sgx_init(), after we make sure at least one of the driver  
>> and the KVM SGX is
>> > > > > > initialized successfully.  Then the code change in this patch  
>> won't be necessary
>> > > > > > if I understand correctly.  AFAICT there's no good reason to  
>> start the ksgxd at
>> > > > > > early stage before we are sure either the driver or KVM SGX  
>> will work.
>> > > > >
>> > > > > I would focus fixing the existing flow rather than reinventing  
>> the flow.
>> > > > >
>> > > > > It can be made to work, and therefore it is IMHO correct action  
>> to take.
>> > > >
>> > > > From another perspective, the *existing flow* is the reason which  
>> causes this
>> > > > bug.  A real fix is to fix the flow itself.
>> > >
>> > > Any existing flow in part of the kernel can have a bug. That
>> > > does not mean that switching flow would be proper way to fix
>> > > a bug.
>> > >
>> > > BR, Jarkko
>> >
>> > Yes but I think this is only true when the flow is reasonable.  If  
>> the flow
>> > itself isn't reasonable, we should fix the flow (given it's easy to  
>> fix AFAICT).
>> >
>> > Anyway, let us also hear from others.
>>
>> The flow can be made to work without issues, which in the
>> context of a bug fix is exactly what a bug fix should do.
>> Not more or less.
>
> No. To me the flow itself is buggy.  There's no reason to start ksgxd()  
> before
> at least SGX driver is initialized to work.
>

Will it cause racing if we expose dev nodes to user space before
ksgxd is started and sensitization done?

> Patching the buggy flow is more like a workaround, but isn't a real fix.
>
>>
>> You don't gain any measurable value for the user with this
>> switch idea.
>
> There is actual gain by moving sgx_page_reclaimer_init() to  
> sgx_drv_init(), or
> only calling sgx_page_reclaimer_init() when sgx_drv_init() returns  
> success:
>
> If somehow sgx_drv_init() fails to initialize, ksgxd() won't run.
>
> Currently, if SGX driver fails to initialize but virtual EPC initializes
> successfully, ksgxd() still runs. However it achieves nothing but only  
> wastes
> CPU cycles.
>
>

You still need ksgxd for sanitizing (at least) and swapping (potentially)
even if only virtual EPC initializes.

Thanks
Haitao