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authorAlexei Starovoitov <ast@kernel.org>2020-01-20 16:53:46 -0800
committerDaniel Borkmann <daniel@iogearbox.net>2020-01-22 23:04:52 +0100
commitbe8704ff07d2374bcc5c675526f95e70c6459683 (patch)
treeba8111a7a61e4efa99f86febd3668c67d0692551 /include/linux/bpf.h
parent2a67a6ccb01f21b854715d86ff6432a18b97adb3 (diff)
bpf: Introduce dynamic program extensions
Introduce dynamic program extensions. The users can load additional BPF functions and replace global functions in previously loaded BPF programs while these programs are executing. Global functions are verified individually by the verifier based on their types only. Hence the global function in the new program which types match older function can safely replace that corresponding function. This new function/program is called 'an extension' of old program. At load time the verifier uses (attach_prog_fd, attach_btf_id) pair to identify the function to be replaced. The BPF program type is derived from the target program into extension program. Technically bpf_verifier_ops is copied from target program. The BPF_PROG_TYPE_EXT program type is a placeholder. It has empty verifier_ops. The extension program can call the same bpf helper functions as target program. Single BPF_PROG_TYPE_EXT type is used to extend XDP, SKB and all other program types. The verifier allows only one level of replacement. Meaning that the extension program cannot recursively extend an extension. That also means that the maximum stack size is increasing from 512 to 1024 bytes and maximum function nesting level from 8 to 16. The programs don't always consume that much. The stack usage is determined by the number of on-stack variables used by the program. The verifier could have enforced 512 limit for combined original plus extension program, but it makes for difficult user experience. The main use case for extensions is to provide generic mechanism to plug external programs into policy program or function call chaining. BPF trampoline is used to track both fentry/fexit and program extensions because both are using the same nop slot at the beginning of every BPF function. Attaching fentry/fexit to a function that was replaced is not allowed. The opposite is true as well. Replacing a function that currently being analyzed with fentry/fexit is not allowed. The executable page allocated by BPF trampoline is not used by program extensions. This inefficiency will be optimized in future patches. Function by function verification of global function supports scalars and pointer to context only. Hence program extensions are supported for such class of global functions only. In the future the verifier will be extended with support to pointers to structures, arrays with sizes, etc. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Andrii Nakryiko <andriin@fb.com> Acked-by: Toke Høiland-Jørgensen <toke@redhat.com> Link: https://lore.kernel.org/bpf/20200121005348.2769920-2-ast@kernel.org
Diffstat (limited to 'include/linux/bpf.h')
-rw-r--r--include/linux/bpf.h10
1 files changed, 9 insertions, 1 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 8e3b8f4ad183..05d16615054c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -465,7 +465,8 @@ void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start);
enum bpf_tramp_prog_type {
BPF_TRAMP_FENTRY,
BPF_TRAMP_FEXIT,
- BPF_TRAMP_MAX
+ BPF_TRAMP_MAX,
+ BPF_TRAMP_REPLACE, /* more than MAX */
};
struct bpf_trampoline {
@@ -480,6 +481,11 @@ struct bpf_trampoline {
void *addr;
bool ftrace_managed;
} func;
+ /* if !NULL this is BPF_PROG_TYPE_EXT program that extends another BPF
+ * program by replacing one of its functions. func.addr is the address
+ * of the function it replaced.
+ */
+ struct bpf_prog *extension_prog;
/* list of BPF programs using this trampoline */
struct hlist_head progs_hlist[BPF_TRAMP_MAX];
/* Number of attached programs. A counter per kind. */
@@ -1107,6 +1113,8 @@ int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
struct bpf_reg_state *regs);
int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
struct bpf_reg_state *reg);
+int btf_check_type_match(struct bpf_verifier_env *env, struct bpf_prog *prog,
+ struct btf *btf, const struct btf_type *t);
struct bpf_prog *bpf_prog_by_id(u32 id);