From afeebf9f57a4965e0be90e4dc87f8f3a1417376d Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Mon, 3 Apr 2023 21:50:28 -0700 Subject: [PATCH] bpf: Undo strict enforcement for walking untagged fields. The commit 6fcd486b3a0a ("bpf: Refactor RCU enforcement in the verifier.") broke several tracing bpf programs. Even in clang compiled kernels there are many fields that are not marked with __rcu that are safe to read and pass into helpers, but the verifier doesn't know that they're safe. Aggressively marking them as PTR_UNTRUSTED was premature. Fixes: 6fcd486b3a0a ("bpf: Refactor RCU enforcement in the verifier.") Signed-off-by: Alexei Starovoitov Signed-off-by: Andrii Nakryiko Acked-by: David Vernet Link: https://lore.kernel.org/bpf/20230404045029.82870-8-alexei.starovoitov@gmail.com --- kernel/bpf/verifier.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index fd90ba498ccc..56f569811f70 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4974,6 +4974,11 @@ static bool is_rcu_reg(const struct bpf_reg_state *reg) return reg->type & MEM_RCU; } +static void clear_trusted_flags(enum bpf_type_flag *flag) +{ + *flag &= ~(BPF_REG_TRUSTED_MODIFIERS | MEM_RCU); +} + static int check_pkt_ptr_alignment(struct bpf_verifier_env *env, const struct bpf_reg_state *reg, int off, int size, bool strict) @@ -5602,8 +5607,8 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env, } else if (flag & (MEM_PERCPU | MEM_USER)) { /* keep as-is */ } else { - /* walking unknown pointers yields untrusted pointer */ - flag = PTR_UNTRUSTED; + /* walking unknown pointers yields old deprecated PTR_TO_BTF_ID */ + clear_trusted_flags(&flag); } } else { /* @@ -5617,7 +5622,7 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env, } } else { /* Old compat. Deprecated */ - flag &= ~PTR_TRUSTED; + clear_trusted_flags(&flag); } if (atype == BPF_READ && value_regno >= 0)