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

From: Bjorn Andersson <bjorn.andersson@linaro.org>
To: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-security-module@vger.kernel.org,
	Chris Wright <chrisw@sous-sol.org>,
	David Howells <dhowells@redhat.com>,
	Alan Cox <alan@linux.intel.com>,
	Kees Cook <keescook@chromium.org>,
	Hans de Goede <hdegoede@redhat.com>,
	Darren Hart <dvhart@infradead.org>,
	Andy Shevchenko <andy@infradead.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
	platform-driver-x86@vger.kernel.org,
	linux-kernel@vger.kernel.org, Peter Jones <pjones@redhat.com>,
	Dave Olsthoorn <dave@bewaar.me>,
	Will Deacon <will.deacon@arm.com>,
	Andy Lutomirski <luto@kernel.org>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	Josh Triplett <josh@joshtriplett.org>,
	dmitry.torokhov@gmail.com, mfuzzey@parkeon.com,
	Kalle Valo <kvalo@codeaurora.org>,
	Arend Van Spriel <arend.vanspriel@broadcom.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	nbroeking@me.com, Torsten Duwe <duwe@suse.de>,
	x86@kernel.org, linux-efi <linux-efi@vger.kernel.org>
Subject: Re: [PATCH v3 2/5] efi: Add embedded peripheral firmware support
Date: Thu, 7 Jun 2018 09:33:07 -0700	[thread overview]
Message-ID: <20180607163307.GO510@tuxbook-pro> (raw)
In-Reply-To: <1524632409.3371.48.camel@linux.vnet.ibm.com>

On Tue 24 Apr 22:00 PDT 2018, Mimi Zohar wrote:
> On Tue, 2018-04-24 at 23:42 +0000, Luis R. Rodriguez wrote:
> > On Tue, Apr 24, 2018 at 12:07:01PM -0400, Mimi Zohar wrote:
> > > On Tue, 2018-04-24 at 17:09 +0200, Hans de Goede wrote:
[..]
> > > > As such the current IMA code (from v4.17-rc2) actually does
> > > > not handle READING_FIRMWARE_PREALLOC_BUFFER at all, 
> > > 
> > > Right, it doesn't yet address READING_FIRMWARE_PREALLOC_BUFFER, but
> > > should.
> > > 
> > > Depending on whether the device requesting the firmware has access to
> > > the DMA memory, before the signature verification, 
> > 
> > It would seem from the original patch review about READING_FIRMWARE_PREALLOC_BUFFER
> > that this is not a DMA buffer.
> 
> The call sequence:
> qcom_mdt_load() -> qcom_scm_pas_init_image() -> dma_alloc_coherent()
> 

qcom_mdt_load() is passed a struct firmware object, which "data" is
passed into qcom_scm_pas_init_image(), which uses dma_alloc_coherent()
to allocate scratch memory to perform a call into secure world. So the
dma_alloc_coherent() here has nothing to do with firmware loading.

qcom_mdt_load() will then use request_firmware_into_buf() to load other
files into the passed void *mem_region, which either comes from a
memremap() or dma_alloc_coherent() call.

> If dma_alloc_coherent() isn't allocating a DMA buffer, then the
> function name is misleading/confusing.
> 

It does allocate memory.

> > 
> > The device driver should have access to the buffer pointer with write given
> > that with request_firmware_into_buf() the driver is giving full write access to
> > the memory pointer so that the firmware API can stuff the firmware it finds
> > there.
> > 
> > Firmware signature verification would be up to the device hardware to do upon
> > load *after* request_firmware_into_buf().
> 
> We're discussing the kernel's signature verification, not the device
> hardware's signature verification.  Can the device driver access the
> buffer, before IMA-appraisal has verified the firmware's signature?
> 

I would expect that it's possible to read the content of the buffer from
a secondary execution context before the request_firmware_into_buf() has
verified the content of the buffer, but I would be considered a
seriously broken driver.

Regards,
Bjorn