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bpf: Undo strict enforcement for walking untagged fields.

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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 <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230404045029.82870-8-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2023-04-03 21:50:28 -07:00 committed by Andrii Nakryiko
parent 30ee9821f9
commit afeebf9f57
1 changed files with 8 additions and 3 deletions
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11
kernel/bpf/verifier.c
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@ -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)