On Tue, 9 Aug 2022 at 02:37, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Mon, Aug 8, 2022 at 6:33 AM Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote: > > > > On Mon, 8 Aug 2022 at 14:41, Artem Savkov <asavkov@xxxxxxxxxx> wrote: > > > > > > On Mon, Aug 08, 2022 at 02:14:33PM +0200, Kumar Kartikeya Dwivedi wrote: > > > > 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. > > > > > > Ok, will do. > > > > > > > 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. > > > > > > This makes sense right now, but if going forward we'll add stricter > > > signing requirements or other prerequisites we'll either have to rename > > > the flag back, or add those as separate flags. I guess the decision here > > > > IMO we should do that when the time comes, for now it should reflect > > the current state. > > But names should be also semantically meaningful, so KF_DESTRUCTIVE > explains that kfunc can do destructive operations, which is better > than just declaring that kfunc needs CAP_SYS_BOOT, as the latter is > current implementation detail which has no bearing on kfunc definition > itself. > > Unless we anticipate we'll have another "destructive" kfunc not using > KF_DESTRUCTIVE and instead we'll add some other > KF_CAP_SYS_WHATEVERELSE? > I just found it a bit odd that KF_DESTRUCTIVE would require CAP_SYS_BOOT. When thinking about what one would write in the docs: just that KF_DESTRUCTIVE kfuncs can do destructive operations? That doesn't really capture what the flag ends up doing to the kfunc (it limits use to those who have a certain cap on program load). There can be several destructive operations (e.g. a frequently mentioned socket kill helper that may be considered equally destructive for some workload) but would probably require CAP_NET_ADMIN instead. But anyway, I didn't really want to bikeshed over this :), we can give it a better name next time something like this is added, and just go with KF_DESTRUCTIVE for now. > > To me this helper requiring cap_sys_boot is just like how some > > existing stable helpers are gated behind bpf_capable or > > perfmon_capable. > > When it requires that the program calling it be signed, we can revisit this. > > > > > depends on whether some of non-destructive bpf programs might ever require > > > CAP_SYS_BOOT capabilities or not. > > > > These are just internal kernel flags, so refactoring/renaming is not a > > big deal when it is needed. E.g. we've changed just how kfuncs are > > registered twice since the support was added not long ago :). > > > > > > > > -- > > > Artem > > >
