On Mon, 8 Aug 2022 at 11:48, 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>
> ---
> include/linux/btf.h | 1 +
> kernel/bpf/verifier.c | 5 +++++
> 2 files changed, 6 insertions(+)
>
> 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 */
>
Please also document this flag in Documentation/bpf/kfuncs.rst.
And maybe instead of KF_DESTRUCTIVE, it might be more apt to call this
KF_CAP_SYS_BOOT. While it is true you had a destructive flag for
programs being loaded earlier, so there was a mapping between the two
UAPI and kfunc flags, what it has boiled down to is that this flag
just requires CAP_SYS_BOOT (in addition to other capabilities) during
load. So that name might express the intent a bit better. We might
soon have similar flags encoding requirements of other capabilities on
load.
The flag rename is just a suggestion, up to you.
> struct btf;
> struct btf_member;
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 096fdac70165..e52ca1631d3f 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -7584,6 +7584,11 @@ 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
>
