From bb88e2174a3059335b34f7c7b5725797e7913d6d Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Sat, 2 Dec 2023 09:56:57 -0800 Subject: [PATCH] bpf: enforce precision of R0 on callback return [ Upstream commit 0acd03a5bd188b0c501d285d938439618bd855c4 ] Given verifier checks actual value, r0 has to be precise, so we need to propagate precision properly. r0 also has to be marked as read, otherwise subsequent state comparisons will ignore such register as unimportant and precision won't really help here. Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper") Acked-by: Eduard Zingerman Acked-by: Shung-Hsi Yu Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/r/20231202175705.885270-4-andrii@kernel.org Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/verifier.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 5d8f352faebda..7318a5d448592 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6244,6 +6244,13 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx) verbose(env, "R0 not a scalar value\n"); return -EACCES; } + + /* we are going to rely on register's precise value */ + err = mark_reg_read(env, r0, r0->parent, REG_LIVE_READ64); + err = err ?: mark_chain_precision(env, BPF_REG_0); + if (err) + return err; + if (!tnum_in(range, r0->var_off)) { verbose_invalid_scalar(env, r0, &range, "callback return", "R0"); return -EINVAL; -- 2.47.3