From 7e3bab2abf42f7fa3f3b4710c8f07343a685c3f1 Mon Sep 17 00:00:00 2001 From: KP Singh Date: Mon, 1 Jun 2026 17:02:44 +0200 Subject: [PATCH] libbpf: Reject non-exclusive metadata maps in the signed loader The loader verifies map->sha against the metadata hash in its instructions. map->sha is calculated when BPF_OBJ_GET_INFO_BY_FD is called on the frozen map. While the map is frozen, the /signed loader/ must also ensure the map is exclusive, as, without exclusivity (which a hostile host could just omit when loading the loader), another BPF program with map access can mutate the contents afterwards, so the check passes on stale data. With the extra check as part of the signed loader, it now refuses to move on with map->sha validation if the host set it up wrongly. Fixes: fb2b0e290147 ("libbpf: Update light skeleton for signing") Signed-off-by: KP Singh Co-developed-by: Daniel Borkmann Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/r/20260601150248.394863-4-daniel@iogearbox.net Signed-off-by: Alexei Starovoitov --- src/gen_loader.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/src/gen_loader.c b/src/gen_loader.c index 3702c59..66a0203 100644 --- a/src/gen_loader.c +++ b/src/gen_loader.c @@ -586,6 +586,23 @@ static void emit_signature_match(struct bpf_gen *gen) __s64 off; int i; + /* + * Reject if the metadata map is not exclusive. Without exclusivity + * the cached map->sha[] verified above can be stale: another BPF + * program with map access could have mutated the contents between + * BPF_OBJ_GET_INFO_BY_FD and loader execution. + */ + emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX, + 0, 0, 0, 0)); + emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, SHA256_DIGEST_LENGTH)); + off = -(gen->insn_cur - gen->insn_start - gen->cleanup_label) / 8 - 2; + if (is_simm16(off)) { + emit(gen, BPF_MOV64_IMM(BPF_REG_7, -EINVAL)); + emit(gen, BPF_JMP_IMM(BPF_JNE, BPF_REG_2, 1, off)); + } else { + gen->error = -ERANGE; + } + for (i = 0; i < SHA256_DWORD_SIZE; i++) { emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX, 0, 0, 0, 0));