On Fri, 2018-08-03 at 08:11 -0500, Seth Forshee wrote: > On Wed, Jul 25, 2018 at 06:31:59PM -0500, Eric Richter wrote: > > IMA can verify the signature of kernel images loaded with kexec_file_load, > > but can not verify images loaded with the regular kexec_load syscall. > > Therefore, the appraisal will automatically fail during kexec_load when an > > appraise policy rule is set for func=KEXEC_KERNEL_CHECK. This can be used > > to effectively disable the kexec_load syscall, while still allowing the > > kexec_file_load to operate so long as the target kernel image is signed. > > > > However, this conflicts with CONFIG_KEXEC_VERIFY_SIG. If that option is > > enabled and there is an appraise rule set, then the target kernel would > > have to be verifiable by both IMA and the architecture specific kernel > > verification procedure. > > > > This patch adds a new func= for IMA appraisal specifically for the original > > kexec_load syscall. Therefore, the kexec_load syscall can be effectively > > disabled via IMA policy, leaving the kexec_file_load syscall able to do its > > own signature verification, and not require it to be signed via IMA. To > > retain compatibility, the existing func=KEXEC_KERNEL_CHECK flag is > > unchanged, and thus enables appraisal for both kexec syscalls. > > This seems like a roundabout way to disallow the kexec_load syscall. > Wouldn't it make more sense to simply disallow kexec_load any time > CONFIG_KEXEC_VERIFY_SIG is enabled, since it effectively renders that > option impotent? Or has that idea already been rejected? Agreed! We can modify the "case LOADING_KEXEC_IMAGE" in ima_load_data() to prevent the kexec_load based on CONFIG_KEXEC_VERIFY_SIG. The architecture specific policy would only include the IMA appraise rule if CONFIG_KEXEC_VERIFY_SIG was not defined. Mimi
