Bpf csum diff #7907
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Bpf csum diff #7907
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The bpf_csum_diff() helper calls csum_partial() which is implemented by some architectures like arm and x86 but other architectures rely on the generic implementation in lib/checksum.c The generic implementation in lib/checksum.c returns a 16 bit value but the arch specific implementations can return more than 16 bits, this works out because before the result is used it is passed through csum_fold() that turns it into a 16-bit value. bpf_csum_diff() directly returns the value from csum_partial() and therefore the values could be different in different architectures. Pass the result of bpf_csum_diff() through from32to16() before returning to homogenize() the result for all architectures. NOTE: from32to16() is used instead of csum_fold() because csum_fold() does from32to16() + bitwise NOT of the result. The result of bpf_csum_diff() can be refed into itself and using csum_fold() would break that usage. Signed-off-by: Puranjay Mohan <[email protected]>
The bpf_csum_diff() helper has been fixed to return a 16-bit value for all archs, so now we don't need to mask the result. This commit is basically reverting the below: 6185266 ("selftests/bpf: Mask bpf_csum_diff() return value to 16 bits in test_verifier") Signed-off-by: Puranjay Mohan <[email protected]>
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