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Date: Wed, 08 Nov 2017 21:17:37 -0500 From: Mimi Zohar <zohar@...ux.vnet.ibm.com> To: "AKASHI, Takahiro" <takahiro.akashi@...aro.org>, "Luis R. Rodriguez" <mcgrof@...nel.org> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Jan Blunck <jblunck@...radead.org>, Julia Lawall <julia.lawall@...6.fr>, David Howells <dhowells@...hat.com>, Marcus Meissner <meissner@...e.de>, Gary Lin <GLin@...e.com>, linux-security-module@...r.kernel.org, gnomes@...rguk.ukuu.org.uk, linux-efi <linux-efi@...r.kernel.org>, linux-kernel@...r.kernel.org, Matthew Garrett <mjg59@...gle.com> Subject: Re: Firmware signing -- Re: [PATCH 00/27] security, efi: Add kernel lockdown > > IMHO that should just fail then, ie, a "locked down" kernel should not want to > > *pass* a firmware signature if such thing could not be done. > > > > Its no different than trying to verify a signed module on a "locked down" for > > which it has no signature. > > > > But perhaps I'm not understanding the issue well, let me know. > > My point is quite simple: > my_deviceA_init() { > err = request_firmware(&fw, "deviceA"); <--- (a) > if (err) > goto err_request; > > err = verify_firmware(fw); <--- (b) > if (err) > goto err_verify; > > load_fw_to_deviceA(fw); <--- (c) > ... > } > > As legacy device drivers does not have (b), there is no chance to > prevent loading a firmware at (c) for locked-down kernel. > > If you allow me to bring in yet another function, say > request_firmware_signable(), which should be used in place of (a) > for all verification-aware drivers, that would be fine. I really don't understand why you need a new function. The request_firmware() eventually calls kernel_read_file_from_path(), which already calls the pre and post LSM hooks. IMA-appraisal is already on these hooks verifying the requested firmware's signature. For systems with "lockdown" enabled, but without IMA-appraisal enabled, define a small, builtin LSM that sits on these LSM hooks and denies the unsigned firmware requests. Mimi > In this case, all the invocation of request_firmware() in legacy code > could be forced to fail in locked-down kernel. > > But I think that "signable" should be allowed to be combined with other > features of request_firmware variants like _(no)wait or _direct. > > -Takahiro AKASHI
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