linux-kernel - Re: [PATCH v2 2/2] x86: sgx_vepc: implement SGX_IOC_VEPC

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Date:   Thu, 14 Oct 2021 15:14:33 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     dave.hansen@...ux.intel.com, seanjc@...gle.com, x86@...nel.org,
        yang.zhong@...el.com, jarkko@...nel.org
Subject: Re: [PATCH v2 2/2] x86: sgx_vepc: implement SGX_IOC_VEPC_REMOVE ioctl

On 10/12/21 3:57 AM, Paolo Bonzini wrote:
> For bare-metal SGX on real hardware, the hardware provides guarantees
> SGX state at reboot.  For instance, all pages start out uninitialized.
> The vepc driver provides a similar guarantee today for freshly-opened
> vepc instances, but guests such as Windows expect all pages to be in
> uninitialized state on startup, including after every guest reboot.
> 
> Some userspace implementations of virtual SGX would rather avoid having
> to close and reopen the /dev/sgx_vepc file descriptor and re-mmap the
> virtual EPC.  For example, they could sandbox themselves after the guest
> starts and forbid further calls to open(), in order to mitigate exploits
> from untrusted guests.
> 
> Therefore, add a ioctl that does this with EREMOVE.  Userspace can
> invoke the ioctl to bring its vEPC pages back to uninitialized state.
> There is a possibility that some pages fail to be removed if they are
> SECS pages, and the child and SECS pages could be in separate vEPC
> regions.  Therefore, the ioctl returns the number of EREMOVE failures,
> telling userspace to try the ioctl again after it's done with all
> vEPC regions.  A more verbose description of the correct usage and
> the possible error conditions is documented in sgx.rst.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

The new approach and revised changelogs look fine to me:

Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>

Like Jarkko mentioned, it would be _nice_ to have some self-contained
selftests around this.  Would it be a pain to rig something up in
selftests/kvm that at least trivially poked at /dev/sgx_vepc?