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[bpf-next,0/4] verifier, improve ptr is_branch_taken logic

Message ID 158983199930.6512.18408887419883363781.stgit@john-Precision-5820-Tower
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Series verifier, improve ptr is_branch_taken logic | expand

Message

John Fastabend May 18, 2020, 8:02 p.m. UTC 
Verifier logic to track pointer is_branch_taken logic to prune paths
that can not be taken. For many types we track if the pointer is null
or not. We can then use this information when calculating if branches
are taken when jump is comparing if pointer is null or not.

First patch is the verifier logic, patches 2/3 are tests for sock
pointers and map values. The final patch adds a printk to one of
the C test cases where the issue was initially reported. Feel free
to drop this if we think its overkill. OTOH it keeps a nice test
of a pattern folks might actually try and also doesn't add much in
the way of test overhead.

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John Fastabend (4):
      bpf: verifier track null pointer branch_taken with JNE and JEQ
      bpf: selftests, verifier case for non null pointer check branch taken
      bpf: selftests, verifier case for non null pointer map value branch
      bpf: selftests, add printk to test_sk_lookup_kern to encode null ptr check


 .../selftests/bpf/progs/test_sk_lookup_kern.c      |    1 +
 .../testing/selftests/bpf/verifier/ref_tracking.c  |   16 ++++++++++++++++
 .../testing/selftests/bpf/verifier/value_or_null.c |   19 +++++++++++++++++++
 3 files changed, 36 insertions(+)

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