On Wed, 2020-05-13 at 16:34 -0700, Kees Cook wrote: > On Wed, May 13, 2020 at 07:00:43PM -0400, Mimi Zohar wrote: > > 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. > > Can the VFS be locked in some way and then using the partial reads would > trigger the "read twice" mode? I.e. something like: > > open > first partial read: > lock file contents (?) > perform full page-at-a-time-read-and-measure > rewind, read partial > other partial reads > final partial read > unlock The security_kernel_read_file(), the pre-hook, would need to be moved after getting the file size, but yes that's exactly what would be done in the pre-hook, when the current offset is 0 and the file size and buffer size aren't the same. Mimi
