From: "Mickaël Salaün" <email@example.com> To: Deven Bowers <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Cc: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [RFC PATCH v3 00/12] Integrity Policy Enforcement LSM (IPE) Date: Thu, 14 May 2020 21:28:15 +0200 Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On 12/05/2020 22:46, Deven Bowers wrote: > > > On 5/11/2020 11:03 AM, Deven Bowers wrote: >> >> >> On 5/10/2020 2:28 AM, Mickaël Salaün wrote: >> >> [...snip] >> >>>> >>>> Additionally, rules are evaluated top-to-bottom. As a result, any >>>> revocation rules, or denies should be placed early in the file to >>>> ensure >>>> that these rules are evaluated before a rule with "action=ALLOW" is >>>> hit. >>>> >>>> IPE policy is designed to be forward compatible and backwards >>>> compatible, >>>> thus any failure to parse a rule will result in the line being ignored, >>>> and a warning being emitted. If backwards compatibility is not >>>> required, >>>> the kernel commandline parameter and sysctl, ipe.strict_parse can be >>>> enabled, which will cause these warnings to be fatal. >>> >>> Ignoring unknown command may lead to inconsistent beaviors. To achieve >>> forward compatibility, I think it would be better to never ignore >>> unknown rule but to give a way to userspace to known what is the current >>> kernel ABI. This could be done with a securityfs file listing the >>> current policy grammar. >>> >> >> That's a fair point. From a manual perspective, I think this is fine. >> A human-user can interpret a grammar successfully on their own when new >> syntax is introduced. >> >> From a producing API perspective, I'd have to think about it a bit >> more. Ideally, the grammar would be structured in such a way that the >> userland >> interpreter of this grammar would not have to be updated once new syntax >> is introduced, avoiding the need to update the userland binary. To do so >> generically ("op=%s") is easy, but doesn't necessarily convey sufficient >> information (what happens when a new "op" token is introduced?). I think >> this may come down to regular expression representations of valid values >> for these tokens, which worries me as regular expressions are incredibly >> error-prone. >> >> I'll see what I can come up with regarding this. > > I have not found a way that I like to expose some kind of grammar > through securityfs that can be understood by usermode to parse the > policy. Here's what I propose as a compromise: > > 1. I remove the unknown command behavior. This address your > first point about inconsistent behaviors, and effectively removes the > strict_parse sysctl (as it is always enabled). > > 2. I introduce a versioning system for the properties > themselves. The valid set of properties and their versions > can be found in securityfs, under say, ipe/config in a key=value > format where `key` indicates the understood token, and `value` > indicates their current version. For example: > > $ cat $SECURITYFS/ipe/config > op=1 > action=1 > policy_name=1 > policy_version=1 > dmverity_signature=1 > dmverity_roothash=1 > boot_verified=1 The name ipe/config sounds like a file to configure IPE. Maybe something like ipe/config_abi or ipe/config_grammar? > > if new syntax is introduced, the version number is increased. > > 3. The format of those versions are documented as part of > the admin-guide around IPE. If user-mode at that point wants to rip > the documentation formats and correlate with the versioning, then > it fulfills the same functionality as above, with out the complexity > around exposing a parsing grammar and interpreting it on-the-fly. > Many of these are unlikely to move past version 1, however. > > Thoughts? > That seems reasonable.
next prev parent reply index Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-04-15 16:25 deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 01/12] scripts: add ipe tooling to generate boot policy deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 02/12] security: add ipe lsm evaluation loop and audit system deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 03/12] security: add ipe lsm policy parser and policy loading deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 04/12] ipe: add property for trust of boot volume deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 05/12] fs: add security blob and hooks for block_device deven.desai 2020-04-22 16:42 ` James Morris 2020-04-22 16:55 ` Casey Schaufler 2020-04-15 16:25 ` [RFC PATCH v3 06/12] dm-verity: move signature check after tree validation deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 07/12] dm-verity: add bdev_setsecurity hook for dm-verity signature deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 08/12] ipe: add property for signed dmverity volumes deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 09/12] dm-verity: add bdev_setsecurity hook for root-hash deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 10/12] ipe: add property for dmverity roothash deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 11/12] documentation: add ipe documentation deven.desai 2020-04-15 16:25 ` [RFC PATCH v3 12/12] cleanup: uapi/linux/audit.h deven.desai 2020-05-10 9:28 ` [RFC PATCH v3 00/12] Integrity Policy Enforcement LSM (IPE) Mickaël Salaün 2020-05-11 18:03 ` Deven Bowers 2020-05-12 20:46 ` Deven Bowers 2020-05-14 19:28 ` Mickaël Salaün [this message] 2020-05-16 22:14 ` Jaskaran Singh Khurana 2020-05-26 20:44 ` Jaskaran Singh Khurana 2020-05-29 8:18 ` Mickaël Salaün
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