linux-kernel - Re: [PATCH v5 1/7] fs: introduce kernel_pread

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Message-ID: <20200513212847.GT11244@42.do-not-panic.com>
Date:   Wed, 13 May 2020 21:28:47 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Mimi Zohar <zohar@...nel.org>
Cc:     Scott Branden <scott.branden@...adcom.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Brown <david.brown@...aro.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>, bjorn.andersson@...aro.org,
        Shuah Khan <skhan@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        Olof Johansson <olof@...om.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Colin Ian King <colin.king@...onical.com>,
        Kees Cook <keescook@...omium.org>,
        Takashi Iwai <tiwai@...e.de>, linux-kselftest@...r.kernel.org,
        Andy Gross <agross@...nel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        linux-integrity <linux-integrity@...r.kernel.org>
Subject: Re: [PATCH v5 1/7] fs: introduce kernel_pread_file* support

On Wed, May 13, 2020 at 05:20:14PM -0400, Mimi Zohar wrote:
> On Wed, 2020-05-13 at 12:41 -0700, Scott Branden wrote:
> > 
> > On 2020-05-13 12:39 p.m., Mimi Zohar wrote:
> > > On Wed, 2020-05-13 at 12:18 -0700, Scott Branden wrote:
> > >> On 2020-05-13 12:03 p.m., Mimi Zohar wrote:
> > >>> On Wed, 2020-05-13 at 11:53 -0700, Scott Branden wrote:
> > >> Even if the kernel successfully verified the firmware file signature it
> > >> would just be wasting its time.  The kernel in these use cases is not always
> > >> trusted.  The device needs to authenticate the firmware image itself.
> > > There are also environments where the kernel is trusted and limits the
> > > firmware being provided to the device to one which they signed.
> > >
> > >>> The device firmware is being downloaded piecemeal from somewhere and
> > >>> won't be measured?
> > >> It doesn't need to be measured for current driver needs.
> > > Sure the device doesn't need the kernel measuring the firmware, but
> > > hardened environments do measure firmware.
> > >
> > >> If someone has such need the infrastructure could be added to the kernel
> > >> at a later date.  Existing functionality is not broken in any way by
> > >> this patch series.
> > > Wow!  You're saying that your patch set takes precedence over the
> > > existing expectations and can break them.
> > Huh? I said existing functionality is NOT broken by this patch series.
> 
> Assuming a system is configured to measure and appraise firmware
> (rules below), with this change the firmware file will not be properly
> measured and will fail signature verification.
> 
> Sample IMA policy rules:
> measure func=FIRMWARE_CHECK
> appraise func=FIRMWARE_CHECK appraise_type=imasig

Would a pre and post lsm hook for pread do it?

  Luis