linux-kernel - Re: [PATCH 0/5 v4] Kexec cmdline bufffer measure

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Date:   Mon, 06 May 2019 08:12:59 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Prakhar Srivastava <prsriva02@...il.com>,
        linux-integrity@...r.kernel.org,
        linux-secuirty-module@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     ebiederm@...ssion.com, vgoyal@...hat.com, nayna@...ux.ibm.com,
        nramas@...rosoft.com, prsriva@...rosoft.com
Subject: Re: [PATCH 0/5 v4] Kexec cmdline bufffer measure

On Fri, 2019-05-03 at 15:25 -0700, Prakhar Srivastava wrote:
> From: Prakhar Srivastava <prsriva02@...il.com>
> 
> For Kexec scenario(kexec_file_load) cmdline args are passed to the
> next kerenel. These cmldine args used to load the next kernel can 
> have undesired/unwanted configs. To guard against any unwanted cmdline
> args being passed to the next kernel. The current kernel should measure
> the cmdline args to the next kernel, the same takes place in the EFI
> bootloader. Thus on kexec the boot_aggregate does not change.

The boot command line is calculated and added to the current running
kernel's measurement list.  On a soft reboot like kexec, the PCRs are
not reset to zero.  Refer to commit 94c3aac567a9 ("ima: on soft
reboot, restore the measurement list") patch description.

> Currently the cmdline args are not measured, this changeset adds a new
> ima and LSM hook for buffer measure and calls into the same to measure
> the cmdline args passed to the next kernel.The cdmline args meassured
> can then be used as an attestation criteria.

Please update this paragraph to reflect the current patch set. 

> 
> The ima logs need to injected into the next kernel, which will be followed
> up by other patchsets.

The log isn't "injected" into the next kernel, but needs to be carried
over, as described in the above referenced commit.

Mimi