On Wed, 2020-07-29 at 12:29 -0400, Mimi Zohar wrote: > On Tue, 2020-07-28 at 12:43 -0700, Kees Cook wrote: > > On Mon, Jul 27, 2020 at 06:57:45AM -0400, Mimi Zohar wrote: > > > On Fri, 2020-07-24 at 14:36 -0700, Kees Cook wrote: > > > > Now that security_post_load_data() is wired up, use it instead > > > > of the NULL file argument style of security_post_read_file(), > > > > and update the security_kernel_load_data() call to indicate that a > > > > security_kernel_post_load_data() call is expected. > > > > > > > > Wire up the IMA check to match earlier logic. Perhaps a generalized > > > > change to ima_post_load_data() might look something like this: > > > > > > > > return process_buffer_measurement(buf, size, > > > > kernel_load_data_id_str(load_id), > > > > read_idmap[load_id] ?: FILE_CHECK, > > > > 0, NULL); > > > > > > > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > > > > > process_measurement() measures, verifies a file signature - both > > > signatures stored as an xattr and as an appended buffer signature - > > > and augments audit records with the file hash. (Support for measuring, > > > augmenting audit records, and/or verifying fs-verity signatures has > > > yet to be added.) > > > > > > As explained in my response to 11/19, the file descriptor provides the > > > file pathname associated with the buffer data. In addition, IMA > > > policy rules may be defined in terms of other file descriptor info - > > > uid, euid, uuid, etc. > > > > > > Recently support was added for measuring the kexec boot command line, > > > certificates being loaded onto a keyring, and blacklisted file hashes > > > (limited to appended signatures). None of these buffers are signed. > > > process_buffer_measurement() was added for this reason and as a > > > result is limited to just measuring the buffer data. > > > > > > Whether process_measurement() or process_buffer_measurement() should > > > be modified, needs to be determined. In either case to support the > > > init_module syscall, would at minimum require the associated file > > > pathname. > > > > Right -- I don't intend to make changes to the init_module() syscall > > since it's deprecated, so this hook is more of a "fuller LSM coverage > > for old syscalls" addition. > > > > IMA can happily continue to ignore it, which is what I have here, but I > > thought I'd at least show what it *might* look like. Perhaps BPF LSM is > > a better example. > > > > Does anything need to change for this patch? > > I wasn't aware that init_syscall was deprecated. From your original comments, > it sounded like you wanted a new LSM for verifying kernel module signatures, > as > they're currently supported via init_module(). > > I was mistaken. Without a file descriptor, security_post_load_data() will > measure the firmware, as Scott confirmed, but won't be able to verify the > signature, whether he signed it using evmctl or not, Actually, the partial firmware read should be calling security_kernel_read_file(). The sysfs firmware fallback is calling security_kernel_load_data(). Which firmware is calling security_kernel_post_load_data()? thanks, Mimi
