From: Alan Maguire <alan.magu...@oracle.com> 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.magu...@oracle.com> Signed-off-by: Toke Høiland-Jørgensen <t...@redhat.com> --- 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 febe8934d19a..b5dbc49fa1a3 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 c2a49df5f921..054b1f7c83f8 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -2112,6 +2112,79 @@ 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_array *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 no chain_progs array is set, that's because the chain call flag + * was not set on program load, and so we can't support chain calls. + */ + if (!prog->aux->chain_progs) + 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->ptrs + index, next_prog); + if (old_prog) + bpf_prog_put(old_prog); + ret = 0; + break; + case BPF_PROG_CHAIN_DEL: + old_prog = xchg(array->ptrs + 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->ptrs + 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, @@ -2884,6 +2957,11 @@ 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);
