From 884c3a18dadfda326dffa364477cc027728219de Mon Sep 17 00:00:00 2001 From: Daniel Xu Date: Tue, 4 Feb 2025 10:25:16 -0700 Subject: [PATCH 1/3] 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)) From 973cb1382ead401c476c82f20525e593ae84788f Mon Sep 17 00:00:00 2001 From: Daniel Xu Date: Tue, 4 Feb 2025 10:25:17 -0700 Subject: [PATCH 2/3] bpf: selftests: Test constant key extraction on irrelevant maps Test that very high constant map keys are not interpreted as an error value by the verifier. This would previously fail. Acked-by: Eduard Zingerman Signed-off-by: Daniel Xu Link: https://lore.kernel.org/r/c0590b62eb9303f389b2f52c0c7e9cf22a358a30.1738689872.git.dxu@dxuuu.xyz Signed-off-by: Alexei Starovoitov --- .../selftests/bpf/progs/verifier_array_access.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/verifier_array_access.c b/tools/testing/selftests/bpf/progs/verifier_array_access.c index 29eb9568633f..0a187ff725cc 100644 --- a/tools/testing/selftests/bpf/progs/verifier_array_access.c +++ b/tools/testing/selftests/bpf/progs/verifier_array_access.c @@ -713,4 +713,19 @@ unsigned int non_stack_key_lookup(void) return val->index; } +SEC("socket") +__description("doesn't reject UINT64_MAX as s64 for irrelevant maps") +__success __retval(42) +unsigned int doesnt_reject_irrelevant_maps(void) +{ + __u64 key = 0xFFFFFFFFFFFFFFFF; + struct test_val *val; + + val = bpf_map_lookup_elem(&map_hash_48b, &key); + if (val) + return val->index; + + return 42; +} + char _license[] SEC("license") = "GPL"; From 7968c6581507052c1c6484ee6c5cbe07381e2dbc Mon Sep 17 00:00:00 2001 From: Daniel Xu Date: Tue, 4 Feb 2025 10:25:18 -0700 Subject: [PATCH 3/3] bpf: verifier: Disambiguate get_constant_map_key() errors Refactor get_constant_map_key() to disambiguate the constant key value from potential error values. In the case that the key is negative, it could be confused for an error. It's not currently an issue, as the verifier seems to track s32 spills as u32. So even if the program wrongly uses a negative value for an arraymap key, the verifier just thinks it's an impossibly high value which gets correctly discarded. Refactor anyways to make things cleaner and prevent potential future issues. Acked-by: Eduard Zingerman Signed-off-by: Daniel Xu Link: https://lore.kernel.org/r/dfe144259ae7cfc98aa63e1b388a14869a10632a.1738689872.git.dxu@dxuuu.xyz Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index e9176a5ce215..98354d781678 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -9149,10 +9149,11 @@ static int check_reg_const_str(struct bpf_verifier_env *env, return 0; } -/* Returns constant key value if possible, else negative error */ -static s64 get_constant_map_key(struct bpf_verifier_env *env, +/* Returns constant key value in `value` if possible, else negative error */ +static int get_constant_map_key(struct bpf_verifier_env *env, struct bpf_reg_state *key, - u32 key_size) + u32 key_size, + s64 *value) { struct bpf_func_state *state = func(env, key); struct bpf_reg_state *reg; @@ -9179,8 +9180,10 @@ static s64 get_constant_map_key(struct bpf_verifier_env *env, /* First handle precisely tracked STACK_ZERO */ for (i = off; i >= 0 && stype[i] == STACK_ZERO; i--) zero_size++; - if (zero_size >= key_size) + if (zero_size >= key_size) { + *value = 0; return 0; + } /* Check that stack contains a scalar spill of expected size */ if (!is_spilled_scalar_reg(&state->stack[spi])) @@ -9203,7 +9206,8 @@ static s64 get_constant_map_key(struct bpf_verifier_env *env, if (err < 0) return err; - return reg->var_off.value; + *value = reg->var_off.value; + return 0; } static bool can_elide_value_nullness(enum bpf_map_type type); @@ -9357,9 +9361,14 @@ skip_type_check: if (err) return err; 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; + err = get_constant_map_key(env, reg, key_size, &meta->const_map_key); + if (err < 0) { + meta->const_map_key = -1; + if (err == -EOPNOTSUPP) + err = 0; + else + return err; + } } break; case ARG_PTR_TO_MAP_VALUE: