On Mon, Oct 07, 2019 at 07:20:37PM +0200, Toke Høiland-Jørgensen wrote: > From: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> > > This adds support for setting and deleting bpf chain call programs through > a couple of new commands in the bpf() syscall. The CHAIN_ADD and CHAIN_DEL > commands take two eBPF program fds and a return code, and install the > 'next' program to be chain called after the 'prev' program if that program > returns 'retcode'. A retcode of -1 means "wildcard", so that the program > will be executed regardless of the previous program's return code. > > > The syscall command names are based on Alexei's prog_chain example[0], > which Alan helpfully rebased on current bpf-next. However, the logic and > program storage is obviously adapted to the execution logic in the previous > commit. > > [0] https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git/commit/?h=prog_chain&id=f54f45d00f91e083f6aec2abe35b6f0be52ae85b&context=15 > > Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx> > Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> > --- > include/uapi/linux/bpf.h | 10 ++++++ > kernel/bpf/syscall.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 88 insertions(+) > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index 1ce80a227be3..b03c23963af8 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -107,6 +107,9 @@ enum bpf_cmd { > BPF_MAP_LOOKUP_AND_DELETE_ELEM, > BPF_MAP_FREEZE, > BPF_BTF_GET_NEXT_ID, > + BPF_PROG_CHAIN_ADD, > + BPF_PROG_CHAIN_DEL, > + BPF_PROG_CHAIN_GET, > }; > > enum bpf_map_type { > @@ -516,6 +519,13 @@ union bpf_attr { > __u64 probe_offset; /* output: probe_offset */ > __u64 probe_addr; /* output: probe_addr */ > } task_fd_query; > + > + struct { /* anonymous struct used by BPF_PROG_CHAIN_* commands */ > + __u32 prev_prog_fd; > + __u32 next_prog_fd; > + __u32 retcode; > + __u32 next_prog_id; /* output: prog_id */ > + }; > } __attribute__((aligned(8))); > > /* The description below is an attempt at providing documentation to eBPF > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index b8a203a05881..be8112e08a88 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -2113,6 +2113,79 @@ static int bpf_prog_test_run(const union bpf_attr *attr, > return ret; > } > > +#define BPF_PROG_CHAIN_LAST_FIELD next_prog_id > + > +static int bpf_prog_chain(int cmd, const union bpf_attr *attr, > + union bpf_attr __user *uattr) > +{ > + struct bpf_prog *prog, *next_prog, *old_prog; > + struct bpf_prog **array; > + int ret = -EOPNOTSUPP; > + u32 index, prog_id; > + > + if (CHECK_ATTR(BPF_PROG_CHAIN)) > + return -EINVAL; > + > + /* Index 0 is wildcard, encoded as ~0 by userspace */ > + if (attr->retcode == ((u32) ~0)) > + index = 0; > + else > + index = attr->retcode + 1; > + > + if (index >= BPF_NUM_CHAIN_SLOTS) > + return -E2BIG; > + > + prog = bpf_prog_get(attr->prev_prog_fd); > + if (IS_ERR(prog)) > + return PTR_ERR(prog); > + > + /* If the chain_calls bit is not set, that's because the chain call flag > + * was not set on program load, and so we can't support chain calls. > + */ > + if (!prog->chain_calls) > + goto out; > + > + array = prog->aux->chain_progs; > + > + switch (cmd) { > + case BPF_PROG_CHAIN_ADD: > + next_prog = bpf_prog_get(attr->next_prog_fd); > + if (IS_ERR(next_prog)) { > + ret = PTR_ERR(next_prog); > + break; > + } > + old_prog = xchg(array + index, next_prog); > + if (old_prog) > + bpf_prog_put(old_prog); > + ret = 0; > + break; How are circular dependencies resolved here? Seems the situation is not prevented, so progs unloaded via XDP won't get the __bpf_prog_free() call where they then drop the references of all the other progs in the chain. > + case BPF_PROG_CHAIN_DEL: > + old_prog = xchg(array + index, NULL); > + if (old_prog) { > + bpf_prog_put(old_prog); > + ret = 0; > + } else { > + ret = -ENOENT; > + } > + break; > + case BPF_PROG_CHAIN_GET: > + old_prog = READ_ONCE(array[index]); > + if (old_prog) { > + prog_id = old_prog->aux->id; > + if (put_user(prog_id, &uattr->next_prog_id)) > + ret = -EFAULT; > + else > + ret = 0; > + } else > + ret = -ENOENT; > + break; > + } > + > +out: > + bpf_prog_put(prog); > + return ret; > +} > + > #define BPF_OBJ_GET_NEXT_ID_LAST_FIELD next_id > > static int bpf_obj_get_next_id(const union bpf_attr *attr, > @@ -2885,6 +2958,11 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz > case BPF_PROG_TEST_RUN: > err = bpf_prog_test_run(&attr, uattr); > break; > + case BPF_PROG_CHAIN_ADD: > + case BPF_PROG_CHAIN_DEL: > + case BPF_PROG_CHAIN_GET: > + err = bpf_prog_chain(cmd, &attr, uattr); > + break; > case BPF_PROG_GET_NEXT_ID: > err = bpf_obj_get_next_id(&attr, uattr, > &prog_idr, &prog_idr_lock); >
