linux-kernel - Re: [PATCH 1/2] x86: sgx_vepc: extract sgx_vepc_remove

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Message-ID: <60c3081434f324a84a565e55a1817510618faf64.camel@kernel.org>
Date:   Tue, 14 Sep 2021 00:00:48 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        dave.hansen@...ux.intel.com, yang.zhong@...el.com
Subject: Re: [PATCH 1/2] x86: sgx_vepc: extract sgx_vepc_remove_page

On Mon, 2021-09-13 at 16:24 +0200, Paolo Bonzini wrote:
> On 13/09/21 16:05, Dave Hansen wrote:
> > On 9/13/21 6:11 AM, Paolo Bonzini wrote:
> > > Windows expects all pages to be in uninitialized state on startup.
> > > In order to implement this, we will need a ioctl that performs
> > > EREMOVE on all pages mapped by a /dev/sgx_vepc file descriptor:
> > > other possibilities, such as closing and reopening the device,
> > > are racy.
> > 
> > Hi Paolo,
> > 
> > How does this end up happening in the first place?
> > 
> > All enclave pages should start out on 'sgx_dirty_page_list' and
> > ksgxd sanitizes them with EREMOVE before making them available.  That
> > should cover EREMOVE after reboots while SGX pages are initialized,
> > including kexec().
> 
> By "Windows startup" I mean even after guest reboot.  Because another 
> process could sneak in and steal your EPC pages between a close() and an 
> open(), I'd like to have a way to EREMOVE the pages while keeping them 
> assigned to the specific vEPC instance, i.e. *without* going through 
> sgx_vepc_free_page().

Isn't "other process in and steal your EPC pages" more like sysadmin
problem, rather than software?

I'm lacking of understanding what would be the collateral damage in
the end.

/Jarkko