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    SubjectRe: [PATCH 3/4] ima: add support for KEXEC_ORIG_KERNEL_CHECK
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    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

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