bpf: Some fixes for nullness elision #4937
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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 <[email protected]>
Reported-by: Marc Hartmayer <[email protected]>
Reported-by: Ilya Leoshkevich <[email protected]>
Tested-by: Marc Hartmayer <[email protected]>
Signed-off-by: Daniel Xu <[email protected]>
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 <[email protected]> Signed-off-by: Daniel Xu <[email protected]>
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 <[email protected]> Signed-off-by: Daniel Xu <[email protected]>
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Pull request for series with
subject: bpf: Some fixes for nullness elision
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=929753