Re: [PATCH 2/2] selftests/bpf: add verifier test for PTR_TO_MEM spill

On Tue, Jan 12, 2021 at 6:17 PM KP Singh [off-list ref] wrote:

On Tue, Jan 12, 2021 at 4:43 PM Daniel Borkmann [off-list ref] wrote:

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On 1/12/21 4:35 PM, Gilad Reti wrote:

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On Tue, Jan 12, 2021 at 4:56 PM KP Singh [off-list ref] wrote:

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On Tue, Jan 12, 2021 at 10:16 AM Gilad Reti [off-list ref] wrote:

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Add test to check that the verifier is able to recognize spilling of
PTR_TO_MEM registers.

It would be nice to have some explanation of what the test does to
recognize the spilling of the PTR_TO_MEM registers in the commit
log as well.

Would it be possible to augment an existing test_progs
program like tools/testing/selftests/bpf/progs/test_ringbuf.c to test
this functionality?

How would you guarantee that LLVM generates the spill/fill, via inline asm?

Yeah, I guess there is no sure-shot way to do it and, adding inline asm would
just be doing the same thing as this verifier test. You can ignore me
on this one :)

It would, however, be nice to have a better description about what the test is
actually doing./

I will re-submit the patch tomorrow. Thank you all for your patience.

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It may be possible, but from what I understood from Daniel's comment here

https://lore.kernel.org/bpf/17629073-4fab-a922-ecc3-25b019960f44@iogearbox.net/ (local)

the test should be a part of the verifier tests (which is reasonable
to me since it is
a verifier bugfix)

Yeah, the test_verifier case as you have is definitely the most straight
forward way to add coverage in this case.