From 10cb8622b6958c2d47961d6a42c76e6c9f1c08f3 Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Mon, 15 May 2023 15:37:47 +0200 Subject: [PATCH] libbpf: Store zero fd to fd_array for loader kfunc relocation When moving some of the test kfuncs to bpf_testmod I hit an issue when some of the kfuncs that object uses are in module and some in vmlinux. The problem is that both vmlinux and module kfuncs get allocated btf_fd_idx index into fd_array, but we store to it the BTF fd value only for module's kfunc, not vmlinux's one because (it's zero). Then after the program is loaded we check if fd_array[btf_fd_idx] != 0 and close the fd. When the object has kfuncs from both vmlinux and module, the fd from fd_array[btf_fd_idx] from previous load will be stored in there for vmlinux's kfunc, so we close unrelated fd (of the program we just loaded in my case). Fixing this by storing zero to fd_array[btf_fd_idx] for vmlinux kfuncs, so the we won't close stale fd. Signed-off-by: Jiri Olsa Link: https://lore.kernel.org/r/20230515133756.1658301-2-jolsa@kernel.org Signed-off-by: Alexei Starovoitov --- tools/lib/bpf/gen_loader.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c index 83e8e3b..cf3323f 100644 --- a/tools/lib/bpf/gen_loader.c +++ b/tools/lib/bpf/gen_loader.c @@ -703,17 +703,17 @@ static void emit_relo_kfunc_btf(struct bpf_gen *gen, struct ksym_relo_desc *relo /* obtain fd in BPF_REG_9 */ emit(gen, BPF_MOV64_REG(BPF_REG_9, BPF_REG_7)); emit(gen, BPF_ALU64_IMM(BPF_RSH, BPF_REG_9, 32)); - /* jump to fd_array store if fd denotes module BTF */ - emit(gen, BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 0, 2)); - /* set the default value for off */ - emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), 0)); - /* skip BTF fd store for vmlinux BTF */ - emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, 4)); /* load fd_array slot pointer */ emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_0, BPF_PSEUDO_MAP_IDX_VALUE, 0, 0, 0, blob_fd_array_off(gen, btf_fd_idx))); - /* store BTF fd in slot */ + /* store BTF fd in slot, 0 for vmlinux */ emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_0, BPF_REG_9, 0)); + /* jump to insn[insn_idx].off store if fd denotes module BTF */ + emit(gen, BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 0, 2)); + /* set the default value for off */ + emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), 0)); + /* skip BTF fd store for vmlinux BTF */ + emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, 1)); /* store index into insn[insn_idx].off */ emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), btf_fd_idx)); log: -- 2.7.4