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

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Message-ID: <20190823212932.GY16384@42.do-not-panic.com>
Date:   Fri, 23 Aug 2019 21:29:32 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Scott Branden <scott.branden@...adcom.com>
Cc:     Takashi Iwai <tiwai@...e.de>,
        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>,
        linux-kselftest@...r.kernel.org, Mimi Zohar <zohar@...ux.ibm.com>
Subject: Re: [PATCH 1/7] fs: introduce kernel_pread_file* support

On Fri, Aug 23, 2019 at 12:55:30PM -0700, Scott Branden wrote:
> Hi Takashi
> 
> On 2019-08-23 5:29 a.m., Takashi Iwai wrote:
> > On Thu, 22 Aug 2019 21:24:45 +0200,
> > Scott Branden wrote:
> > > Add kernel_pread_file* support to kernel to allow for partial read
> > > of files with an offset into the file.  Existing kernel_read_file
> > > functions call new kernel_pread_file functions with offset=0 and
> > > flags=KERNEL_PREAD_FLAG_WHOLE.
> > Would this change passes the security check like ima?
> > I thought security_kernel_post_read_file() checks the whole content
> > for calculating the hash...
> 
> It passes the fw_run_tests.sh.  How do you test the firmware loader passes
> this security check?

Its not a security check per code, its an audit of the code, to ensure
that no new cases are not covered and its why I had CC'd Mimi. The
question lies in *if* the approach exposes a new interface which cannot
be attested. Its unclear to me if we can attest currently through
security modules the fallback interface, as there are not APIs with a
respective callback yet.

  Luis