On Thu, Feb 20, 2020 at 06:52:45PM +0100, KP Singh wrote: > From: KP Singh <kpsingh@xxxxxxxxxx> > > The BPF LSM programs are implemented as fexit trampolines to avoid the > overhead of retpolines. These programs cannot be attached to security_* > wrappers as there are quite a few security_* functions that do more than > just calling the LSM callbacks. > > This was discussed on the lists in: > > https://lore.kernel.org/bpf/20200123152440.28956-1-kpsingh@xxxxxxxxxxxx/T/#m068becce588a0cdf01913f368a97aea4c62d8266 > > Adding a NOP callback after all the static LSM callbacks are called has > the following benefits: > > - The BPF programs run at the right stage of the security_* wrappers. > - They run after all the static LSM hooks allowed the operation, > therefore cannot allow an action that was already denied. > > There are some hooks which do not call call_int_hooks or > call_void_hooks. It's not possible to call the bpf_lsm_* functions > without checking if there is BPF LSM program attached to these hooks. > This is added further in a subsequent patch. For now, these hooks are > marked as NO_BPF (i.e. attachment of BPF programs is not possible). the commit log doesn't match the code. > + > +/* For every LSM hook that allows attachment of BPF programs, declare a NOP > + * function where a BPF program can be attached as an fexit trampoline. > + */ > +#define LSM_HOOK(RET, NAME, ...) LSM_HOOK_##RET(NAME, __VA_ARGS__) > +#define LSM_HOOK_int(NAME, ...) noinline int bpf_lsm_##NAME(__VA_ARGS__) \ Did you check generated asm? I think I saw cases when gcc ignored 'noinline' when function is defined in the same file and still performed inlining while keeping the function body. To be safe I think __weak is necessary. That will guarantee noinline. And please reduce your cc next time. It's way too long.
