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    Subject[PATCH 5.6 049/166] bpf: Reliably preserve btf_trace_xxx types
    Date
    From: Andrii Nakryiko <andriin@fb.com>

    [ Upstream commit 441420a1f0b3031f228453697406c86f110e59d4 ]

    btf_trace_xxx types, crucial for tp_btf BPF programs (raw tracepoint with
    verifier-checked direct memory access), have to be preserved in kernel BTF to
    allow verifier do its job and enforce type/memory safety. It was reported
    ([0]) that for kernels built with Clang current type-casting approach doesn't
    preserve these types.

    This patch fixes it by declaring an anonymous union for each registered
    tracepoint, capturing both struct bpf_raw_event_map information, as well as
    recording btf_trace_##call type reliably. Structurally, it's still the same
    content as for a plain struct bpf_raw_event_map, so no other changes are
    necessary.

    [0] https://github.com/iovisor/bcc/issues/2770#issuecomment-591007692

    Fixes: e8c423fb31fa ("bpf: Add typecast to raw_tracepoints to help BTF generation")
    Reported-by: Wenbo Zhang <ethercflow@gmail.com>
    Signed-off-by: Andrii Nakryiko <andriin@fb.com>
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>
    Acked-by: Yonghong Song <yhs@fb.com>
    Link: https://lore.kernel.org/bpf/20200301081045.3491005-2-andriin@fb.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    include/trace/bpf_probe.h | 18 +++++++++++-------
    1 file changed, 11 insertions(+), 7 deletions(-)

    diff --git a/include/trace/bpf_probe.h b/include/trace/bpf_probe.h
    index b04c292709730..1ce3be63add1f 100644
    --- a/include/trace/bpf_probe.h
    +++ b/include/trace/bpf_probe.h
    @@ -75,13 +75,17 @@ static inline void bpf_test_probe_##call(void) \
    check_trace_callback_type_##call(__bpf_trace_##template); \
    } \
    typedef void (*btf_trace_##call)(void *__data, proto); \
    -static struct bpf_raw_event_map __used \
    - __attribute__((section("__bpf_raw_tp_map"))) \
    -__bpf_trace_tp_map_##call = { \
    - .tp = &__tracepoint_##call, \
    - .bpf_func = (void *)(btf_trace_##call)__bpf_trace_##template, \
    - .num_args = COUNT_ARGS(args), \
    - .writable_size = size, \
    +static union { \
    + struct bpf_raw_event_map event; \
    + btf_trace_##call handler; \
    +} __bpf_trace_tp_map_##call __used \
    +__attribute__((section("__bpf_raw_tp_map"))) = { \
    + .event = { \
    + .tp = &__tracepoint_##call, \
    + .bpf_func = __bpf_trace_##template, \
    + .num_args = COUNT_ARGS(args), \
    + .writable_size = size, \
    + }, \
    };

    #define FIRST(x, ...) x
    --
    2.20.1


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