Commit afeebf9f authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Andrii Nakryiko
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bpf: Undo strict enforcement for walking untagged fields. 



The commit 6fcd486b ("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: 6fcd486b ("bpf: Refactor RCU enforcement in the verifier.")
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230404045029.82870-8-alexei.starovoitov@gmail.com
parent 30ee9821

kernel/bpf/verifier.c

+8 −3
Original line number Diff line number Diff line
@@ -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)