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Message-ID: <1589404814.5098.185.camel@kernel.org>
Subject: Re: [PATCH v5 1/7] fs: introduce kernel_pread_file* support
From:   Mimi Zohar <zohar@kernel.org>
To:     Scott Branden <scott.branden@broadcom.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        David Brown <david.brown@linaro.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Shuah Khan <shuah@kernel.org>, bjorn.andersson@linaro.org,
        Shuah Khan <skhan@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>
Cc:     "Rafael J . Wysocki" <rafael@kernel.org>,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-fsdevel@vger.kernel.org,
        BCM Kernel Feedback <bcm-kernel-feedback-list@broadcom.com>,
        Olof Johansson <olof@lixom.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Colin Ian King <colin.king@canonical.com>,
        Kees Cook <keescook@chromium.org>,
        Takashi Iwai <tiwai@suse.de>, linux-kselftest@vger.kernel.org,
        Andy Gross <agross@kernel.org>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        linux-integrity <linux-integrity@vger.kernel.org>
Date:   Wed, 13 May 2020 17:20:14 -0400
In-Reply-To: <a228ae0f-d551-e0e8-446e-5ae63462c520@broadcom.com>
References: <20200508002739.19360-1-scott.branden@broadcom.com>
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         <1589395153.5098.158.camel@kernel.org>
         <0e6b5f65-8c61-b02e-7d35-b4ae52aebcf3@broadcom.com>
         <1589396593.5098.166.camel@kernel.org>
         <e1b92047-7003-0615-3d58-1388ec27c78a@broadcom.com>
         <1589398747.5098.178.camel@kernel.org>
         <a228ae0f-d551-e0e8-446e-5ae63462c520@broadcom.com>
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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

Mimi