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bpf: remove incorrect 'verifier bug' warning 

The BPF verifier checks the maximum number of call stack frames twice,
first in the main CFG traversal (do_check) and then in a subsequent
traversal (check_max_stack_depth).  If the second check fails, it logs a
'verifier bug' warning and errors out, as the number of call stack frames
should have been verified already.

However, the second check may fail without indicating a verifier bug: if
the excessive function calls reside in dead code, the main CFG traversal
may not visit them; the subsequent traversal visits all instructions,
including dead code.

This case raises the question of how invalid dead code should be treated.
This patch implements the conservative option and rejects such code.

Signed-off-by: Paul Chaignon <paul.chaignon@orange.com>
Tested-by: Xiao Han <xiao.han@orange.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Paul Chaignon 2019-03-20 13:58:27 +01:00 committed by Alexei Starovoitov
parent 1da6c4d914
commit 927cb78177
1 changed files with 3 additions and 2 deletions
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5
kernel/bpf/verifier.c
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@ -1897,8 +1897,9 @@ static int check_max_stack_depth(struct bpf_verifier_env *env)
}
frame++;
if (frame >= MAX_CALL_FRAMES) {
WARN_ONCE(1, "verifier bug. Call stack is too deep\n");
return -EFAULT;
verbose(env, "the call stack of %d frames is too deep !\n",
frame);
return -E2BIG;
}
goto process_func;
}