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Add fd_array_cnt attribute for BPF_PROG_LOAD #8148

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Add fd_array_cnt attribute for BPF_PROG_LOAD #8148

wants to merge 7 commits into from
+524 −83

Commits on Dec 3, 2024

  1. bpf: add a __btf_get_by_fd helper 

    Add a new helper to get a pointer to a struct btf from a file
descriptor. This helper doesn't increase a refcnt. Add a comment
explaining this and pointing to a corresponding function which
does take a reference.

Signed-off-by: Anton Protopopov <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
    @aspsk
    aspsk authored and Kernel Patches Daemon committed Dec 3, 2024
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  2. bpf: move map/prog compatibility checks 

    Move some inlined map/prog compatibility checks from the
resolve_pseudo_ldimm64() function to the dedicated
check_map_prog_compatibility() function. Call the latter function
from the add_used_map_from_fd() function directly.

This simplifies code and optimizes logic a bit, as before these
changes the check_map_prog_compatibility() function was executed on
every map usage, which doesn't make sense, as it doesn't include any
per-instruction checks, only map type vs. prog type.

(This patch also simplifies a consequent patch which will call the
add_used_map_from_fd() function from another code path.)

Signed-off-by: Anton Protopopov <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
    @aspsk
    aspsk authored and Kernel Patches Daemon committed Dec 3, 2024
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  3. bpf: add fd_array_cnt attribute for prog_load 

    The fd_array attribute of the BPF_PROG_LOAD syscall may contain a set
of file descriptors: maps or btfs. This field was introduced as a
sparse array. Introduce a new attribute, fd_array_cnt, which, if
present, indicates that the fd_array is a continuous array of the
corresponding length.

If fd_array_cnt is non-zero, then every map in the fd_array will be
bound to the program, as if it was used by the program. This
functionality is similar to the BPF_PROG_BIND_MAP syscall, but such
maps can be used by the verifier during the program load.

Signed-off-by: Anton Protopopov <[email protected]>
    @aspsk
    aspsk authored and Kernel Patches Daemon committed Dec 3, 2024
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  4. libbpf: prog load: allow to use fd_array_cnt 

    Add new fd_array_cnt field to bpf_prog_load_opts
and pass it in bpf_attr, if set.

Signed-off-by: Anton Protopopov <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
    @aspsk
    aspsk authored and Kernel Patches Daemon committed Dec 3, 2024
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  5. selftests/bpf: Add tests for fd_array_cnt 

    Add a new set of tests to test the new field in PROG_LOAD-related
part of bpf_attr: fd_array_cnt.

Add the following test cases:

  * fd_array_cnt/no-fd-array: program is loaded in a normal
    way, without any fd_array present

  * fd_array_cnt/fd-array-ok: pass two extra non-used maps,
    check that they're bound to the program

  * fd_array_cnt/fd-array-dup-input: pass a few extra maps,
    only two of which are unique

  * fd_array_cnt/fd-array-ref-maps-in-array: pass a map in
    fd_array which is also referenced from within the program

  * fd_array_cnt/fd-array-trash-input: pass array with some trash

  * fd_array_cnt/fd-array-with-holes: pass an array with holes (fd=0)

  * fd_array_cnt/fd-array-2big: pass too large array

All the tests above are using the bpf(2) syscall directly,
no libbpf involved.

Signed-off-by: Anton Protopopov <[email protected]>
    @aspsk
    aspsk authored and Kernel Patches Daemon committed Dec 3, 2024
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  6. bpf: fix potential error return 

    The bpf_remove_insns() function returns WARN_ON_ONCE(error), where
error is a result of bpf_adj_branches(), and thus should be always 0
However, if for any reason it is not 0, then it will be converted to
boolean by WARN_ON_ONCE and returned to user space as 1, not an actual
error value. Fix this by returning the original err after the WARN check.

Signed-off-by: Anton Protopopov <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
    @aspsk
    aspsk authored and Kernel Patches Daemon committed Dec 3, 2024
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  7. selftest/bpf: replace magic constants by macros 

    Replace magic constants in a BTF structure initialization code by
proper macros, as is done in other similar selftests.

Signed-off-by: Anton Protopopov <[email protected]>
Suggested-by: Eduard Zingerman <[email protected]>
    @aspsk
    aspsk authored and Kernel Patches Daemon committed Dec 3, 2024
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