bpf/verifier: allow kfunc to return an allocated mem

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For drivers (outside of network), the incoming data is not statically
defined in a struct. Most of the time the data buffer is kzalloc-ed
and thus we can not rely on eBPF and BTF to explore the data.

This commit allows to return an arbitrary memory, previously allocated by
the driver.
An interesting extra point is that the kfunc can mark the exported
memory region as read only or read/write.

So, when a kfunc is not returning a pointer to a struct but to a plain
type, we can consider it is a valid allocated memory assuming that:
- one of the arguments is either called rdonly_buf_size or
  rdwr_buf_size
- and this argument is a const from the caller point of view

We can then use this parameter as the size of the allocated memory.

The memory is either read-only or read-write based on the name
of the size parameter.

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Link: https://lore.kernel.org/r/20220906151303.2780789-7-benjamin.tissoires@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

...

This commit is contained in:

Benjamin Tissoires 2022-09-06 17:13:02 +02:00 • committed by Alexei Starovoitov

parent f9b348185f

commit eb1f7f71c1

5 changed files with 133 additions and 34 deletions

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9

include/linux/bpf.h

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2

include/linux/bpf_verifier.h

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10

include/linux/btf.h

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101

kernel/bpf/btf.c

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45

kernel/bpf/verifier.c

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