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    SubjectRe: [RFC PATCH net-next 0/5] bpf: rewrite value tracking in verifier
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    From: Edward Cree <ecree@solarflare.com>
    Date: Wed, 7 Jun 2017 15:55:57 +0100

    > This series simplifies alignment tracking, generalises bounds tracking and
    > fixes some bounds-tracking bugs in the BPF verifier. Pointer arithmetic on
    > packet pointers, stack pointers, map value pointers and context pointers has
    > been unified, and bounds on these pointers are only checked when the pointer
    > is dereferenced.
    > Operations on pointers which destroy all relation to the original pointer
    > (such as multiplies and shifts) are disallowed if !env->allow_ptr_leaks,
    > otherwise they convert the pointer to an unknown scalar and feed it to the
    > normal scalar arithmetic handling.
    > Pointer types have been unified with the corresponding adjusted-pointer types
    > where those existed (e.g. PTR_TO_MAP_VALUE[_ADJ] or FRAME_PTR vs
    > PTR_TO_STACK); similarly, CONST_IMM and UNKNOWN_VALUE have been unified into
    > SCALAR_VALUE.
    > Pointer types (except CONST_PTR_TO_MAP, PTR_TO_MAP_VALUE_OR_NULL and
    > PTR_TO_PACKET_END, which do not allow arithmetic) have a 'fixed offset' and
    > a 'variable offset'; the former is used when e.g. adding an immediate or a
    > known-constant register, as long as it does not overflow. Otherwise the
    > latter is used, and any operation creating a new variable offset creates a
    > new 'id' (and, for PTR_TO_PACKET, clears the 'range').
    > SCALAR_VALUEs use the 'variable offset' fields to track the range of possible
    > values; the 'fixed offset' should never be set on a scalar.
    >
    > Patch 2/5 is rather on the big side, but since it changes the contents and
    > semantics of a fairly central data structure, I'm not really sure how to go
    > about splitting it up further without producing broken intermediate states.
    >
    > With the changes in patch 5/5, all tools/testing/selftests/bpf/test_verifier
    > tests pass.

    Edward, I haven't had a chance to review this yet, but I wanted to thank you
    for working on this.

    I will find some time to test your work on sparc too.

    Thanks again!

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