Messages in this thread | | | From | Kees Cook <> | Date | Sat, 14 Jul 2018 19:34:19 -0700 | Subject | Re: [PATCH v6 8/8] ima: based on policy warn about loading firmware (pre-allocated buffer) |
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On Fri, Jul 13, 2018 at 11:06 AM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote: > Some systems are memory constrained but they need to load very large > firmwares. The firmware subsystem allows drivers to request this > firmware be loaded from the filesystem, but this requires that the > entire firmware be loaded into kernel memory first before it's provided > to the driver. This can lead to a situation where we map the firmware > twice, once to load the firmware into kernel memory and once to copy the > firmware into the final resting place. > > To resolve this problem, commit a098ecd2fa7d ("firmware: support loading > into a pre-allocated buffer") introduced request_firmware_into_buf() API > that allows drivers to request firmware be loaded directly into a > pre-allocated buffer. > > Do devices using pre-allocated memory run the risk of the firmware being > accessible to the device prior to the completion of IMA's signature > verification any more than when using two buffers? (Refer to mailing list > discussion[1]). > > Only on systems with an IOMMU can the access be prevented. As long as > the signature verification completes prior to the DMA map is performed, > the device can not access the buffer. This implies that the same buffer > can not be re-used. Can we ensure the buffer has not been DMA mapped > before using the pre-allocated buffer? > > [1] https://lkml.org/lkml/2018/7/10/56 > > Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com> > Cc: Luis R. Rodriguez <mcgrof@suse.com> > Cc: Stephen Boyd <sboyd@kernel.org> > Cc: Bjorn Andersson <bjorn.andersson@linaro.org> > Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
I can't decide if it's worth adding the link (maybe using the lkml.kernel.org url[1]) directly in the code or not.
Either way:
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
[1] https://lkml.kernel.org/r/CAKv+Gu-knHeBRGqo+2pb3X9cCjwovEykoXUf=DZyP7aJpoS60A@mail.gmail.com
-- Kees Cook Pixel Security
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