From: Jarkko Sakkinen <jarkko@kernel.org>
To: Reinette Chatre <reinette.chatre@intel.com>
Cc: linux-sgx@vger.kernel.org,
Nathaniel McCallum <nathaniel@profian.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3] x86/sgx: Do not limit EAUG'd pages by pre-initialization policy
Date: Sat, 5 Mar 2022 03:59:56 +0200 [thread overview]
Message-ID: <YiLEHBlXAz+sUheO@kernel.org> (raw)
In-Reply-To: <684930a2-a247-7d5e-90e8-6e80db618c4c@intel.com>
On Fri, Mar 04, 2022 at 11:09:36AM -0800, Reinette Chatre wrote:
> Hi Jarkko,
>
> On 3/3/2022 7:39 PM, Jarkko Sakkinen wrote:
> > Pre-initialization policy is meant for EADD'd pages because they are
> > part of the enclave identity. It's a good practice to not let touch the
> > permissions after initialization, and does provide guarantees to e.g.
> > LSM's about the enclave.
>
> I disagree. There are scenarios where it is indeed good practice to
> modify the permissions after initialization. For example, pages that
> may be used for relocatable code can start with RWX permissions but once
> the pages have been populated with the code they should be able to restrict
> permissions to RX only. It is not good practice to require RWX permission
> over their entire lifetime. Ideally pages should only have the lowest
> permissions possible.
The only permissions kernel has real control is PTE permissions when
the enclave has been initialized.
You are introducing an artificial limitation with vm_run_prot_bits
that makes e.g. EMODPE more costly for no good reason, and in-kernel
variable has nothing to do with the permissions. They are located
in EPCM.
> Supporting the modification of permissions after initialization enables
> the security conscious enclave owner to support the security
> principle of least privilege.
1. Kernel has the control of PTE permissions.
2. Enclave has the control of EPCM permissions.
vm_run_prot_bits does not help making anything more secure.
BR, Jarkko
prev parent reply other threads:[~2022-03-05 2:00 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-04 3:39 [PATCH v3] x86/sgx: Do not limit EAUG'd pages by pre-initialization policy Jarkko Sakkinen
2022-03-04 19:09 ` Reinette Chatre
2022-03-05 1:59 ` Jarkko Sakkinen [this message]
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