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SubjectRe: [PATCH 07/11] kexec: Disable in a secure boot environment
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On Tue, 2012-09-04 at 11:55 -0400, Matthew Garrett wrote:
> kexec could be used as a vector for a malicious user to use a signed kernel
> to circumvent the secure boot trust model. In the long run we'll want to
> support signed kexec payloads, but for the moment we should just disable
> loading entirely in that situation.
>
> Signed-off-by: Matthew Garrett <mjg@redhat.com>
> ---
> kernel/kexec.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index 0668d58..48852ec 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -944,7 +944,7 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
> int result;
>
> /* We only trust the superuser with rebooting the system. */
> - if (!capable(CAP_SYS_BOOT))
> + if (!capable(CAP_SYS_BOOT) || !capable(CAP_SECURE_FIRMWARE))
> return -EPERM;
>
> /*

Normally capabilities provide additional permissions. So if you don't
have the capability, an errno is returned. CAP_SYS_BOOT is a good
example. With CAP_SECURE_FIRMWARE, it reads backwards - if not
CAP_SECURE_FIRMWARE, return error. I think you want to invert the name
to CAP_NOT_SECURE_FIRMWARE, CAP_NOT_SECURE_BOOT or perhaps
CAP_UNSECURED_BOOT.

Mimi



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