On 2026/7/22 15:39, Philo Lu wrote:
From: Daniel Borkmann <[email protected]> commit ee861486e377edc55361c08dcbceab3f6b6577bd upstream. Usage of ld_{abs,ind} instructions got extended into subprogs some time ago via commit 09b28d76eac4 ("bpf: Add abnormal return checks."). These are only allowed in subprograms when the latter are BTF annotated and have scalar return types. The code generator in bpf_gen_ld_abs() has an abnormal exit path (r0=0 + exit) from legacy cBPF times. While the enforcement is on scalar return types, the verifier must also simulate the path of abnormal exit if the packet data load via ld_{abs,ind} failed. This is currently not the case. Fix it by having the verifier simulate both success and failure paths, and extend it in similar ways as we do for tail calls. The success path (r0=unknown, continue to next insn) is pushed onto stack for later validation and the r0=0 and return to the caller is done on the fall-through side. Fixes: 09b28d76eac4 ("bpf: Add abnormal return checks.") Reported-by: STAR Labs SG <[email protected]> Signed-off-by: Daniel Borkmann <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Alexei Starovoitov <[email protected]> [ Dropped visit_abnormal_return_insn changes: depends on 7.0 symbols from e40f5a6bf88a ("bpf: correct stack liveness for tail calls"); Hunk1: adapted IS_ERR/PTR_ERR to !branch/-EFAULT to match push_stack() NULL-on-failure convention. ]
These versions does not introduce consumers corresponding to the output of jump tables; therefore, the assignment of jump tables is not involved. Reviewed-by: Pu Lehui <[email protected]>
Signed-off-by: Philo Lu <[email protected]> --- kernel/bpf/verifier.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f638b2d3a42fb..3f74767e47484 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -15119,6 +15119,23 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn) mark_reg_unknown(env, regs, BPF_REG_0); /* ld_abs load up to 32-bit skb data. */ regs[BPF_REG_0].subreg_def = env->insn_idx + 1; + /* + * See bpf_gen_ld_abs() which emits a hidden BPF_EXIT with r0=0 + * which must be explored by the verifier when in a subprog. + */ + if (env->cur_state->curframe) { + struct bpf_verifier_state *branch; + + mark_reg_scratched(env, BPF_REG_0); + branch = push_stack(env, env->insn_idx + 1, env->insn_idx, false); + if (!branch) + return -EFAULT; + mark_reg_known_zero(env, regs, BPF_REG_0); + err = prepare_func_exit(env, &env->insn_idx); + if (err) + return err; + env->insn_idx--; + } return 0; } -- 2.47.3
