From 62561eb442bd095f06534ce637b116b278e5e912 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Tue, 15 Oct 2019 11:28:47 -0700 Subject: [PATCH] libbpf: Add support for field existance CO-RE relocation Add support for BPF_FRK_EXISTS relocation kind to detect existence of captured field in a destination BTF, allowing conditional logic to handle incompatible differences between kernels. Also introduce opt-in relaxed CO-RE relocation handling option, which makes libbpf emit warning for failed relocations, but proceed with other relocations. Instruction, for which relocation failed, is patched with (u32)-1 value. Signed-off-by: Andrii Nakryiko Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20191015182849.3922287-4-andriin@fb.com --- tools/lib/bpf/libbpf.c | 74 +++++++++++++++++++++++++++++++++++++++----------- tools/lib/bpf/libbpf.h | 4 ++- 2 files changed, 61 insertions(+), 17 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index db3308b..8d56559 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -249,6 +249,7 @@ struct bpf_object { bool loaded; bool has_pseudo_calls; + bool relaxed_core_relocs; /* * Information when doing elf related work. Only valid if fd @@ -2771,26 +2772,54 @@ static int bpf_core_spec_match(struct bpf_core_spec *local_spec, /* * Patch relocatable BPF instruction. - * Expected insn->imm value is provided for validation, as well as the new - * relocated value. + * + * Patched value is determined by relocation kind and target specification. + * For field existence relocation target spec will be NULL if field is not + * found. + * Expected insn->imm value is determined using relocation kind and local + * spec, and is checked before patching instruction. If actual insn->imm value + * is wrong, bail out with error. * * Currently three kinds of BPF instructions are supported: * 1. rX = (assignment with immediate operand); * 2. rX += (arithmetic operations with immediate operand); - * 3. *(rX) = (indirect memory assignment with immediate operand). - * - * If actual insn->imm value is wrong, bail out. */ -static int bpf_core_reloc_insn(struct bpf_program *prog, int insn_off, - __u32 orig_off, __u32 new_off) +static int bpf_core_reloc_insn(struct bpf_program *prog, + const struct bpf_field_reloc *relo, + const struct bpf_core_spec *local_spec, + const struct bpf_core_spec *targ_spec) { + __u32 orig_val, new_val; struct bpf_insn *insn; int insn_idx; __u8 class; - if (insn_off % sizeof(struct bpf_insn)) + if (relo->insn_off % sizeof(struct bpf_insn)) return -EINVAL; - insn_idx = insn_off / sizeof(struct bpf_insn); + insn_idx = relo->insn_off / sizeof(struct bpf_insn); + + switch (relo->kind) { + case BPF_FIELD_BYTE_OFFSET: + orig_val = local_spec->offset; + if (targ_spec) { + new_val = targ_spec->offset; + } else { + pr_warning("prog '%s': patching insn #%d w/ failed reloc, imm %d -> %d\n", + bpf_program__title(prog, false), insn_idx, + orig_val, -1); + new_val = (__u32)-1; + } + break; + case BPF_FIELD_EXISTS: + orig_val = 1; /* can't generate EXISTS relo w/o local field */ + new_val = targ_spec ? 1 : 0; + break; + default: + pr_warning("prog '%s': unknown relo %d at insn #%d'\n", + bpf_program__title(prog, false), + relo->kind, insn_idx); + return -EINVAL; + } insn = &prog->insns[insn_idx]; class = BPF_CLASS(insn->code); @@ -2798,12 +2827,12 @@ static int bpf_core_reloc_insn(struct bpf_program *prog, int insn_off, if (class == BPF_ALU || class == BPF_ALU64) { if (BPF_SRC(insn->code) != BPF_K) return -EINVAL; - if (insn->imm != orig_off) + if (insn->imm != orig_val) return -EINVAL; - insn->imm = new_off; + insn->imm = new_val; pr_debug("prog '%s': patched insn #%d (ALU/ALU64) imm %d -> %d\n", bpf_program__title(prog, false), - insn_idx, orig_off, new_off); + insn_idx, orig_val, new_val); } else { pr_warning("prog '%s': trying to relocate unrecognized insn #%d, code:%x, src:%x, dst:%x, off:%x, imm:%x\n", bpf_program__title(prog, false), @@ -2811,6 +2840,7 @@ static int bpf_core_reloc_insn(struct bpf_program *prog, int insn_off, insn->off, insn->imm); return -EINVAL; } + return 0; } @@ -3087,15 +3117,26 @@ static int bpf_core_reloc_field(struct bpf_program *prog, cand_ids->data[j++] = cand_spec.spec[0].type_id; } - cand_ids->len = j; - if (cand_ids->len == 0) { + /* + * For BPF_FIELD_EXISTS relo or when relaxed CO-RE reloc mode is + * requested, it's expected that we might not find any candidates. + * In this case, if field wasn't found in any candidate, the list of + * candidates shouldn't change at all, we'll just handle relocating + * appropriately, depending on relo's kind. + */ + if (j > 0) + cand_ids->len = j; + + if (j == 0 && !prog->obj->relaxed_core_relocs && + relo->kind != BPF_FIELD_EXISTS) { pr_warning("prog '%s': relo #%d: no matching targets found for [%d] %s + %s\n", prog_name, relo_idx, local_id, local_name, spec_str); return -ESRCH; } - err = bpf_core_reloc_insn(prog, relo->insn_off, - local_spec.offset, targ_spec.offset); + /* bpf_core_reloc_insn should know how to handle missing targ_spec */ + err = bpf_core_reloc_insn(prog, relo, &local_spec, + j ? &targ_spec : NULL); if (err) { pr_warning("prog '%s': relo #%d: failed to patch insn at offset %d: %d\n", prog_name, relo_idx, relo->insn_off, err); @@ -3587,6 +3628,7 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz, if (IS_ERR(obj)) return obj; + obj->relaxed_core_relocs = OPTS_GET(opts, relaxed_core_relocs, false); relaxed_maps = OPTS_GET(opts, relaxed_maps, false); CHECK_ERR(bpf_object__elf_init(obj), err, out); diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h index 667e685..53ce212 100644 --- a/tools/lib/bpf/libbpf.h +++ b/tools/lib/bpf/libbpf.h @@ -96,8 +96,10 @@ struct bpf_object_open_opts { const char *object_name; /* parse map definitions non-strictly, allowing extra attributes/data */ bool relaxed_maps; + /* process CO-RE relocations non-strictly, allowing them to fail */ + bool relaxed_core_relocs; }; -#define bpf_object_open_opts__last_field relaxed_maps +#define bpf_object_open_opts__last_field relaxed_core_relocs LIBBPF_API struct bpf_object *bpf_object__open(const char *path); LIBBPF_API struct bpf_object * -- 2.7.4