On Tue, 9 Aug 2022 at 12:53, Artem Savkov <asavkov@xxxxxxxxxx> wrote:
>
> Add KF_DESTRUCTIVE flag for destructive functions. Functions with this
> flag set will require CAP_SYS_BOOT capabilities.
>
> Signed-off-by: Artem Savkov <asavkov@xxxxxxxxxx>
> ---
> Documentation/bpf/kfuncs.rst | 9 +++++++++
> include/linux/btf.h | 1 +
> kernel/bpf/verifier.c | 5 +++++
> 3 files changed, 15 insertions(+)
>
> diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
> index c0b7dae6dbf5..2e97e08be7de 100644
> --- a/Documentation/bpf/kfuncs.rst
> +++ b/Documentation/bpf/kfuncs.rst
> @@ -146,6 +146,15 @@ that operate (change some property, perform some operation) on an object that
> was obtained using an acquire kfunc. Such kfuncs need an unchanged pointer to
> ensure the integrity of the operation being performed on the expected object.
>
> +2.4.5 KF_DESTRUCTIVE flag
This should be 2.4.6.
> +--------------------------
> +
> +The KF_DESTRUCTIVE flag is used to indicate functions calling which is
> +destructive to the system. For example such a call can result in system
> +rebooting or panicking. Due to this additional restrictions apply to these
> +calls. At the moment they only require CAP_SYS_BOOT capability, but more can be
> +added later.
> +
> 2.5 Registering the kfuncs
> --------------------------
>
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index cdb376d53238..51a0961c84e3 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -49,6 +49,7 @@
> * for this case.
> */
> #define KF_TRUSTED_ARGS (1 << 4) /* kfunc only takes trusted pointer arguments */
> +#define KF_DESTRUCTIVE (1 << 5) /* kfunc performs destructive actions */
>
> struct btf;
> struct btf_member;
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 843a966cd02b..163cc0a2dc5a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -7598,6 +7598,11 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> func_name);
> return -EACCES;
> }
> + if (*kfunc_flags & KF_DESTRUCTIVE && !capable(CAP_SYS_BOOT)) {
> + verbose(env, "destructive kfunc calls require CAP_SYS_BOOT capabilities\n");
> + return -EACCES;
> + }
> +
> acq = *kfunc_flags & KF_ACQUIRE;
>
> /* Check the arguments */
> --
> 2.37.1
>
