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 <eddyz87@gmail.com>
Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Reported-by: Ilya Leoshkevich <iii@linux.ibm.com>
Tested-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Link: https://lore.kernel.org/r/aa868b642b026ff87ba6105ea151bc8693b35932.1738689872.git.dxu@dxuuu.xyz
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9971c03adfd5d69645e057dc9f8f55ecdd45f908..e9176a5ce215ea7206448cb5a6e51291b5705a21 100644 (file)
--- 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))