linux-kernel - Re: [PATCH v3 2/5] efi: Add embedded peripheral firmware support

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Message-ID: <71e6a45a-398d-b7a4-dab0-8b9936683226@redhat.com>
Date:   Tue, 24 Apr 2018 17:09:52 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>
Cc:     Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Jones <pjones@...hat.com>,
        Dave Olsthoorn <dave@...aar.me>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        David Howells <dhowells@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        dmitry.torokhov@...il.com, mfuzzey@...keon.com,
        Kalle Valo <kvalo@...eaurora.org>,
        Arend Van Spriel <arend.vanspriel@...adcom.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        nbroeking@...com, bjorn.andersson@...aro.org,
        Torsten Duwe <duwe@...e.de>, x86@...nel.org,
        linux-efi@...r.kernel.org
Subject: Re: [PATCH v3 2/5] efi: Add embedded peripheral firmware support

Hi,

On 23-04-18 23:11, Luis R. Rodriguez wrote:
> Hans, please see use of READING_FIRMWARE_PREALLOC_BUFFER, we'll need a new ID
> and security for this type of request so IMA can reject it if the policy is
> configured for it.

Hmm, interesting, actually it seems like the whole existence
of READING_FIRMWARE_PREALLOC_BUFFER is a mistake, the IMA
framework really does not care if we are loading the firmware
into memory allocated by the firmware-loader code, or into
memory allocated by the device-driver requesting the firmware.

As such the current IMA code (from v4.17-rc2) actually does
not handle READING_FIRMWARE_PREALLOC_BUFFER at all, here
are bits of code from: security/integrity/ima/ima_main.c:

static int read_idmap[READING_MAX_ID] = {
         [READING_FIRMWARE] = FIRMWARE_CHECK,
         [READING_MODULE] = MODULE_CHECK,
         [READING_KEXEC_IMAGE] = KEXEC_KERNEL_CHECK,
         [READING_KEXEC_INITRAMFS] = KEXEC_INITRAMFS_CHECK,
         [READING_POLICY] = POLICY_CHECK
};

int ima_post_read_file(struct file *file, void *buf, loff_t size,
	...
         if (!file && read_id == READING_FIRMWARE) {
                 if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
                     (ima_appraise & IMA_APPRAISE_ENFORCE))
                         return -EACCES; /* INTEGRITY_UNKNOWN */
                 return 0;
         }

Which show that the IMA code is not handling
READING_FIRMWARE_PREALLOC_BUFFER as it should (I believe it
should handle it the same as READING_FIRMWARE).

Now we could fix that, but the only user of
READING_FIRMWARE_PREALLOC_BUFFER is the code which originally
introduced it:

https://patchwork.kernel.org/patch/9162011/

So I believe it might be better to instead replace it
with just READING_FIRMWARE and find another way to tell
kernel_read_file() that there is a pre-allocated buffer,
perhaps the easiest way there is that  *buf must be
NULL when the caller wants kernel_read_file() to
vmalloc the mem. This would of course require auditing
all callers that the buf which the pass in is initialized
to NULL.

Either way adding a third READING_FIRMWARE_FOO to the
kernel_read_file_id enum seems like a bad idea, from
the IMA pov firmware is firmware.

What this whole exercise has shown me though is that
I need to call security_kernel_post_read_file() when
loading EFI embedded firmware. I will add a call to
security_kernel_post_read_file() for v4 of the patch-set.

> Please Cc Kees in future patches.

Will do.

Regards,

Hans