On Wed, 2020-05-13 at 15:48 -0700, Scott Branden wrote: > > On 2020-05-13 3:12 p.m., Mimi Zohar wrote: > > On Wed, 2020-05-13 at 21:28 +0000, Luis Chamberlain wrote: > >> On Wed, May 13, 2020 at 05:20:14PM -0400, Mimi Zohar wrote: > >>> 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. > So no existing functionality has been broken. > >>> > >>> Sample IMA policy rules: > >>> measure func=FIRMWARE_CHECK > >>> appraise func=FIRMWARE_CHECK appraise_type=imasig > >> Would a pre and post lsm hook for pread do it? > > IMA currently measures and verifies the firmware file signature on the > > post hook. The file is read once into a buffer. With this change, > > IMA would need to be on the pre hook, to read the entire file, > > calculating the file hash and verifying the file signature. Basically > > the firmware would be read once for IMA and again for the device. > The entire file may not fit into available memory to measure and > verify. Hence the reason for a partial read. Previously, IMA pre-read the file in page size chunks in order to calculate the file hash. To avoid reading the file twice, the file is now read into a buffer. > > Is there some way we could add a flag when calling the > request_firmware_into_buf to indicate it is ok that the data requested > does not need to be measured? The decision as to what needs to be measured is a policy decision left up to the system owner, which they express by loading an IMA policy. Mimi
