Messages in this thread | | | Subject | Re: [PATCH bpf-next v4 3/8] bpf: lsm: provide attachment points for BPF LSM programs | From | Casey Schaufler <> | Date | Thu, 20 Feb 2020 15:49:05 -0800 |
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On 2/20/2020 9:52 AM, KP Singh wrote: > From: KP Singh <kpsingh@google.com>
Sorry about the heavy list pruning - the original set blows thunderbird up.
> > 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@chromium.org/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.
I still say that the special call-out to BPF is unnecessary. I remain unconvinced by the arguments. You aren't doing anything so special that the general mechanism won't work.
> > 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). > > Signed-off-by: KP Singh <kpsingh@google.com> > --- > include/linux/bpf_lsm.h | 34 ++++++++++++++++++++++++++++++++++ > kernel/bpf/bpf_lsm.c | 16 ++++++++++++++++ > security/security.c | 3 +++ > 3 files changed, 53 insertions(+) > create mode 100644 include/linux/bpf_lsm.h > > diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h > new file mode 100644 > index 000000000000..f867f72f6aa9 > --- /dev/null > +++ b/include/linux/bpf_lsm.h > @@ -0,0 +1,34 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > + > +/* > + * Copyright 2019 Google LLC. > + */ > + > +#ifndef _LINUX_BPF_LSM_H > +#define _LINUX_BPF_LSM_H > + > +#include <linux/bpf.h> > + > +#ifdef CONFIG_BPF_LSM > + > +#define LSM_HOOK(RET, NAME, ...) RET bpf_lsm_##NAME(__VA_ARGS__); > +#include <linux/lsm_hook_names.h> > +#undef LSM_HOOK > + > +#define RUN_BPF_LSM_VOID_PROGS(FUNC, ...) bpf_lsm_##FUNC(__VA_ARGS__) > +#define RUN_BPF_LSM_INT_PROGS(RC, FUNC, ...) ({ \ > + do { \ > + if (RC == 0) \ > + RC = bpf_lsm_##FUNC(__VA_ARGS__); \ > + } while (0); \ > + RC; \ > +}) > + > +#else /* !CONFIG_BPF_LSM */ > + > +#define RUN_BPF_LSM_INT_PROGS(RC, FUNC, ...) (RC) > +#define RUN_BPF_LSM_VOID_PROGS(FUNC, ...) > + > +#endif /* CONFIG_BPF_LSM */ > + > +#endif /* _LINUX_BPF_LSM_H */ > diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c > index affb6941622e..abc847c9b9a1 100644 > --- a/kernel/bpf/bpf_lsm.c > +++ b/kernel/bpf/bpf_lsm.c > @@ -7,6 +7,22 @@ > #include <linux/filter.h> > #include <linux/bpf.h> > #include <linux/btf.h> > +#include <linux/bpf_lsm.h> > + > +/* 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__) \ > +{ \ > + return 0; \ > +} > + > +#define LSM_HOOK_void(NAME, ...) \ > + noinline void bpf_lsm_##NAME(__VA_ARGS__) {} > + > +#include <linux/lsm_hook_names.h> > +#undef LSM_HOOK > > const struct bpf_prog_ops lsm_prog_ops = { > }; > diff --git a/security/security.c b/security/security.c > index 565bc9b67276..aa111392a700 100644 > --- a/security/security.c > +++ b/security/security.c > @@ -28,6 +28,7 @@ > #include <linux/string.h> > #include <linux/msg.h> > #include <net/flow.h> > +#include <linux/bpf_lsm.h> > > #define MAX_LSM_EVM_XATTR 2 > > @@ -684,6 +685,7 @@ static void __init lsm_early_task(struct task_struct *task) > \ > hlist_for_each_entry(P, &security_hook_heads.FUNC, list) \ > P->hook.FUNC(__VA_ARGS__); \ > + RUN_BPF_LSM_VOID_PROGS(FUNC, __VA_ARGS__); \
> } while (0) > > #define call_int_hook(FUNC, IRC, ...) ({ \ > @@ -696,6 +698,7 @@ static void __init lsm_early_task(struct task_struct *task) > if (RC != 0) \ > break; \ > } \ > + RC = RUN_BPF_LSM_INT_PROGS(RC, FUNC, __VA_ARGS__); \ > } while (0); \ > RC; \ > })
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