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bpf: Introduce fd_idx

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Typical program loading sequence involves creating bpf maps and applying
map FDs into bpf instructions in various places in the bpf program.
This job is done by libbpf that is using compiler generated ELF relocations
to patch certain instruction after maps are created and BTFs are loaded.
The goal of fd_idx is to allow bpf instructions to stay immutable
after compilation. At load time the libbpf would still create maps as usual,
but it wouldn't need to patch instructions. It would store map_fds into
__u32 fd_array[] and would pass that pointer to sys_bpf(BPF_PROG_LOAD).

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210514003623.28033-9-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov
2021-05-13 17:36:10 -07:00
committed by Daniel Borkmann
parent 2341d6bb13
commit 387544bfa2
5 changed files with 61 additions and 21 deletions
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16
tools/include/uapi/linux/bpf.h
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@@ -1098,8 +1098,8 @@ enum bpf_link_type {
/* When BPF ldimm64's insn[0].src_reg != 0 then this can have
* the following extensions:
*
* insn[0].src_reg: BPF_PSEUDO_MAP_FD
* insn[0].imm: map fd
* insn[0].src_reg: BPF_PSEUDO_MAP_[FD|IDX]
* insn[0].imm: map fd or fd_idx
* insn[1].imm: 0
* insn[0].off: 0
* insn[1].off: 0
@@ -1107,15 +1107,19 @@ enum bpf_link_type {
* verifier type: CONST_PTR_TO_MAP
*/
#define BPF_PSEUDO_MAP_FD 1
/* insn[0].src_reg: BPF_PSEUDO_MAP_VALUE
* insn[0].imm: map fd
#define BPF_PSEUDO_MAP_IDX 5
/* insn[0].src_reg: BPF_PSEUDO_MAP_[IDX_]VALUE
* insn[0].imm: map fd or fd_idx
* insn[1].imm: offset into value
* insn[0].off: 0
* insn[1].off: 0
* ldimm64 rewrite: address of map[0]+offset
* verifier type: PTR_TO_MAP_VALUE
*/
#define BPF_PSEUDO_MAP_VALUE 2
#define BPF_PSEUDO_MAP_VALUE 2
#define BPF_PSEUDO_MAP_IDX_VALUE 6
/* insn[0].src_reg: BPF_PSEUDO_BTF_ID
* insn[0].imm: kernel btd id of VAR
* insn[1].imm: 0
@@ -1315,6 +1319,8 @@ union bpf_attr {
/* or valid module BTF object fd or 0 to attach to vmlinux */
__u32 attach_btf_obj_fd;
};
__u32 :32; /* pad */
__aligned_u64 fd_array; /* array of FDs */
};
struct { /* anonymous struct used by BPF_OBJ_* commands */