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From: Mimi Zohar <zohar@linux.ibm.com>
To: Roberto Sassu <roberto.sassu@huawei.com>, mjg59@srcf.ucam.org
Cc: linux-integrity@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 00/12] evm: Improve usability of portable signatures
Date: Thu, 20 May 2021 14:55:41 -0400	[thread overview]
Message-ID: <2804f10fa77b58b4992f56ea36a36d4f1e3f4b24.camel@linux.ibm.com> (raw)
In-Reply-To: <20210514152753.982958-1-roberto.sassu@huawei.com>

On Fri, 2021-05-14 at 17:27 +0200, Roberto Sassu wrote:
> EVM portable signatures are particularly suitable for the protection of
> metadata of immutable files where metadata is signed by a software vendor.
> They can be used for example in conjunction with an IMA policy that
> appraises only executed and memory mapped files.
> 
> However, until now portable signatures can be properly installed only if
> the EVM_ALLOW_METADATA_WRITES initialization flag is also set, which
> disables metadata verification until an HMAC key is loaded. This will cause
> metadata writes to be allowed even in the situations where they shouldn't
> (metadata protected by a portable signature is immutable).
> 
> The main reason why setting the flag is necessary is that the operations
> necessary to install portable signatures and protected metadata would be
> otherwise denied, despite being legitimate, due to the fact that the
> decision logic has to avoid an unsafe recalculation of the HMAC that would
> make the unsuccessfully verified metadata valid. However, the decision
> logic is too coarse, and does not fully take into account all the possible
> situations where metadata operations could be allowed.
> 
> For example, if the HMAC key is not loaded and it cannot be loaded in the
> future due the EVM_SETUP_COMPLETE flag being set, it wouldn't be a problem
> to allow metadata operations, as they wouldn't result in an HMAC being
> recalculated.
> 
> This patch set extends the decision logic and adds the necessary exceptions
> to use portable signatures without turning off metadata verification and
> deprecates the EVM_ALLOW_METADATA_WRITES flag.

Thanks, Roberto.

Applied to: git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-
integrity.git 
next-integrity-testing

Mimi



  parent reply	other threads:[~2021-05-20 18:56 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-14 15:27 [PATCH v7 00/12] evm: Improve usability of portable signatures Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 01/12] evm: Execute evm_inode_init_security() only when an HMAC key is loaded Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 02/12] evm: Load EVM key in ima_load_x509() to avoid appraisal Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 03/12] evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 04/12] evm: Introduce evm_revalidate_status() Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 05/12] evm: Introduce evm_hmac_disabled() to safely ignore verification errors Roberto Sassu
2021-05-20  8:48   ` [RESEND][PATCH " Roberto Sassu
2021-05-20  8:51     ` Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 06/12] evm: Allow xattr/attr operations for portable signatures Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 07/12] evm: Pass user namespace to set/remove xattr hooks Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 08/12] evm: Allow setxattr() and setattr() for unmodified metadata Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 09/12] evm: Deprecate EVM_ALLOW_METADATA_WRITES Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 10/12] ima: Allow imasig requirement to be satisfied by EVM portable signatures Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 11/12] ima: Introduce template field evmsig and write to field sig as fallback Roberto Sassu
2021-05-14 15:27 ` [PATCH v7 12/12] ima: Don't remove security.ima if file must not be appraised Roberto Sassu
2021-05-20 18:55 ` Mimi Zohar [this message]
2021-05-21  7:07   ` [PATCH v7 00/12] evm: Improve usability of portable signatures Roberto Sassu
2021-05-21 17:31     ` Mimi Zohar

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