From 884c3a18dadfda326dffa364477cc027728219de Mon Sep 17 00:00:00 2001 From: Daniel Xu Date: Tue, 4 Feb 2025 10:25:16 -0700 Subject: [PATCH] bpf: verifier: Do not extract constant map keys for irrelevant maps Previously, we were trying to extract constant map keys for all bpf_map_lookup_elem(), regardless of map type. This is an issue if the map has a u64 key and the value is very high, as it can be interpreted as a negative signed value. This in turn is treated as an error value by check_func_arg() which causes a valid program to be incorrectly rejected. Fix by only extracting constant map keys for relevant maps. This fix works because nullness elision is only allowed for {PERCPU_}ARRAY maps, and keys for these are within u32 range. See next commit for an example via selftest. Acked-by: Eduard Zingerman Reported-by: Marc Hartmayer Reported-by: Ilya Leoshkevich Tested-by: Marc Hartmayer Signed-off-by: Daniel Xu Link: https://lore.kernel.org/r/aa868b642b026ff87ba6105ea151bc8693b35932.1738689872.git.dxu@dxuuu.xyz Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9971c03adfd5..e9176a5ce215 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -9206,6 +9206,8 @@ static s64 get_constant_map_key(struct bpf_verifier_env *env, return reg->var_off.value; } +static bool can_elide_value_nullness(enum bpf_map_type type); + static int check_func_arg(struct bpf_verifier_env *env, u32 arg, struct bpf_call_arg_meta *meta, const struct bpf_func_proto *fn, @@ -9354,9 +9356,11 @@ skip_type_check: err = check_helper_mem_access(env, regno, key_size, BPF_READ, false, NULL); if (err) return err; - meta->const_map_key = get_constant_map_key(env, reg, key_size); - if (meta->const_map_key < 0 && meta->const_map_key != -EOPNOTSUPP) - return meta->const_map_key; + if (can_elide_value_nullness(meta->map_ptr->map_type)) { + meta->const_map_key = get_constant_map_key(env, reg, key_size); + if (meta->const_map_key < 0 && meta->const_map_key != -EOPNOTSUPP) + return meta->const_map_key; + } break; case ARG_PTR_TO_MAP_VALUE: if (type_may_be_null(arg_type) && register_is_null(reg))