On 20-Feb 18:25, Alexei Starovoitov wrote: > 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. Fixed. Thanks! > > > + > > +/* 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. Sure, will change it to __weak. > > And please reduce your cc next time. It's way too long. Will do. - KP
